CA1328917C - Apparatus and method for providing digital audio on the sound carrier of a standard television signal - Google Patents

Abstract

ABSTRACT
A television transmission system replaces the standard FM audio portion of a television signal with digital audio. Three digital audio channels are time division multiplexed on the sound carrier, using combined multi-phase and AM modulation. The audio signals are digitized using adaptive delta modulation techniques. Video vertical and horizontal framing, as well as the audio carrier phase reference, audio data bit time and frame reference, and various control data is carried using AM modulation. The digital audio information is carried using multi-phase modulation.
The composite data stream may be serially encrypted to provide security and prevent unauthorized reproduction of the video and/or audio portions of the television signal.

Description

APPARATUS AND METHOD FOR PROVIDING DIGITAL
. _ _ _ _ _ AUDIO ON THE SOUND CARRIER OF A STANDARD_ TELEVISION SIGNAL

BACKGROUND OF THE INVENTION
.

The present invention relates to television broadcasting and reception, and more particularly to a method and apparatus for providing high quality digital sound signals within the audio portion of a standard television signal.
New digital techniques for the reproduction of sound provide performance that is far superior to analog techniques which have been used in the past.
An example of high fidelity sound reproduction using digital techniques can be found in the compact disk technology which has recently enjoyed tremendous success as an alternative to phonograph records and tapes. Digital recording and playback technigues provide reproduction of music that is extremely realistic and absent from background noise and distortions which have plagued other high fidelity sound reproduction systems currently in wide scale use.
Recent advances in television technology have enabled the transmission of stereophonic sound together with a conventional television picture transmission. Known systems have used analog techniques in connection with the stereophonic sound reproduction. See, for example, commoniy assigned and 132~ql7 issued U.S. patent no. 4,646,150, issued February 24, 1987 and entitled "Apparatus and Method for Stereo Televislon Sound".
A difficulty Wlth providing digital audio in television broadcasting has been the incorporation of the digital signals withln the standard television signal without interfering with the video portions of the television signal or appreciably affecting the quality or type of picture reproduced by conventional video circuits.
In addition, any television distribution system which transmits digital audio data (such as a cable television system) must be such that the transmitted television signal can be received and reproduced on the millions of television sets already in existence which use conventional analog sound circuits. Thus, such things as the channel width of six megahertz (MHz) for each channel within the television signal spectrum, the aspect ratio of four to three, the video bandwidth of 4.25 MHz, the horizontal and vertical scanning rates of 15.734 kilohertz (KHz) and 60 hertz (Hz), respectively, and the number of scanning lines per frame at 525 cannot be changed, subject to narrow tolerances.

~ 3 ~3~891~

The pre3ent invention provlde~ a rnet)~od and appara tu~ f or i ncorpor~t i ng d 191 t 1 zed aud lo dat~
witt~ln the sound carrier of a standard televlsion slqnal in ~ rnanner such that the ~lgnal ~111 b~
S recoverabl~ for reproduction of th~ transm~tted proqram on black ~nd wh~te and color televlsion ~ts ~1 r~dy i n ex 1~ tenc~ .

SUMMARY OF THE INVENTION

In accordance with the present invention, a method and apparatus are provided for transmitting, receiving, and reproducing digital audio signals in the sound carrier of a standard television signal. An audio signal is digitized using, for example, adaptive delta modulati~n techniques. Several channels of audio information, such as left and right stereo channels and a second audio program ("SAP") channel can all be digitized and incorporated onto the television signal sound carrier. The digitized audio signal is modulated using multi-phase modulation on the sound carrier portion of a television signal. The modulated sound carrier is then converted to an intermediate frequency, and summed with the AM modulated video portion of the television signal to which the digitized audio signal corresponds to produce a composite IF output signal.
The sound carrier is amplitude modulated with a pilot signal for use as a phase and timing reference in the multi-phase modulated signal. The pilot signal can comprise, for example, a pulse added to the sound carrier once for each horizontal line contained in the television signal. The pilot sisnal can be added to a portion of the sound carrier corresponding to the end of active video on each horizontal line.
In order to broadcast the composite IF output signal, it can be converted to an RF output signal and transmitted on a television signal channel. The RF
output signal can be transmitted through the air, via 5 1328ql7 satellite~ over a cable television system, or any combination thereof, In the instance wh0re the television signal contain~ premium programming such as that which would be offered on a pay-per-view basis via satellite or a cable television system, the video portion of the signal can be scrambled by suppressing the horizontal synchronization pulses thereof, Such scrambling will not interfere with the proper transmission and subsequent reception and reproduction of the digital audio signal. The digital audio data can also be encrypted to prevent unauthorized reproduction of ~he audio portion of a television program.
In accordance with the present invention, the adaptive delta m~dulation used to digitize the audio signal uses an audio sampling rate that is an integer factor of the sound carrier center frequency. Further, the sound carrier center frequency is phase locked to a horizontal scan rate used in reproducing the video portion of the television signal. In a preferred embodiment, the horizontal scan rate is approximately 15.734 KHz and the sound carrier center frequency is 4.5 MHz.
In order to provide stereo left, stereo right, and second audio program ("SAP") audio channels, these three channels can be time division multiplexed on the audio carrier of the television signal. The digitizing of the three audio channels can be accomplished by sampling the left and right stereo ~ t :

1328ql7 audio channels at an adaptive delta modulation rate of 13 times the horizontal scan rate, and sampling the SAP channel at an adaptive delta modulation rate of 11 times the horizontal scan rate. The composite data stream may be serially encrypted for security purposes.
The present invention also provides a method and apparatus for receiving the television signal with the digital audio data incorporated therein and reproducing the sound which the digital signals represent, A multi-phase demodulator demodulates a received television signal to retrieve the audio channel data. The data is presented to an adaptive delta modulation decoder which produces conventional audio output signals for input to an audio amplifier or, alternately, a television modulator which inputs the audio signals (now in analog form) to a - television for sound reproduction in a conventional manner.

1 328q 1 7 BRIE~ DESCRIPrION OF T~it ~IING8 Figure l is a dlagra~ ~how~ng the complet~ Yldeo ~pectrum of a ~tandard color televl~lon transmiaslon~
Plgure 2 i8 A graphlc~l repre~entation sho~lng tho interleavlng of th~ lum~nan~e and digltal audio ~lgnals wltb color ~lgn~ls ln the ~r~qu~ncy spectru~
of a tel~vislon signal~
Pigure 3 18 a block dlbgra~ of a cabls telo~i810n h~adend wh~ch modulate~ and add8 diglt~l ~udlo ~lgn~18 to a t~levision ~lgnal ln accordance ~lth tho pre~nt lnvention~
Figure 4 i8 ~ block di~gram o~ 8 ~ultl-p~a80 modulator for use in modulating the dlg1tal ~udlo infor~ation in accord~nce wlth th~ pre~ent inv~ntion~
lS Figure S ~ a block diagram of a cable television converter for recelving and reproducing tel~vislon ~ignals wlth digital audio data in accordance ~it~ t~e present invention:
Pigure 6 ls a block diagra~ of a ~ulti~p~d~e demodulator for u~e 1" the converter s~own in ~lgurs 5s Figure 7 i~ a polar diagram illu~trating the multi-phase modulation technique used in accordance with the present invention;
Figure 8 depict~ various waveforms including the ~ulti-phase modulated input, detected peak AM, detected most significant bit, and detected least signif lcant b' ~ infor~atlon from a televi~ion ~ignal having dlgit21 audio data in accordance with the present ~nvas~tion;

1 32~9 1 7 Figure 9 18 a loglc dlagram o~ a data encryptor/decryptor u~ed to encode or decode dlgltal data transmltted wlth a televlslon slgnal~
Fi~ure lO 18 ~ timlng diagra~ of horlzontal synchronlz~tlon and data pul~e~s and Figure ll 1~ a tlming dlagram of AM ~odulated data wlthin a portlon of a vldeo lnformatlon frame.

1 328q ~ 7 Figure 1 illustrates the compl~te video ~pectrum of a standard c~lor televlslon transmi~sion. Th~
lumlnance slgnal 14 i8 shown in grap~ 10, and the color or chromlnance~ slgn~l 20 1~ 3hown in g~h 12.
A color ~ubcarrler 16 1~ tran~mitted at 3.5795~5 MH~
with ~idebands that ext~nd 0.6 M~z sbove ~nd 1.5 M~z below th~s frequency. The sound c~rrler 18 1 centered ~t 4.5 The u~ of the ~pecifl~ frequency of 3.57g5~5 ~H~
for the chrominance subcarrier r~ults ln ~n ~nterle~ving o~ the lumlnanc~ and chro~in~nce slgnal~
a~ i3 well known in th~ art. Th~ lnterleaving of ~ignal~ makes lt possibl~ to transmlt both thc luminance and chromlnance slgnal~ w~thin the ~ame channel width used for the transmls~lon of a monoc~rome telavl~ion ~ignal.
In ~t~ndard monochro~e t~l~vision slgnal transmi~ion, ths tran~mittcd signal ~8 conprls~d of recurring wave for~s having frequencle~ that ar~
harmoni C8 of the ~orizontal line ~canning ~requency.
Thus~ the frequency spectrum contains a concentrat~on of energy at each harmonic, $.e., at whole multiple3 of the horizontal line frequency. Pigure 2 illustrates thç frequencies at which such concentrations of energy occur. A f~r~t concentratlon appear~ at the line frequency 29. Subsequent coneen~rations of energy are centered around the ~ecor.d harmonic 31, ~h~ third harmonic 33, and 30 forth as ~hown at the 226th h~rmonic 35, 227th 1 32~9 1 7 I armonic 37, 228th harmon~c 39, and 229th harmonlc 41.
shown ln ~lgure 2, nearly hal~ o~ the video spectrum 18 unused by th~ lumlnanc~ signal ~hlch has harmonlcs at whole multiple~ of the 11na frequency.
Therefore, in providing color telev~s10n tran~1s~10n, l wa8 posslblQ tO lnterleave t~e chrominance ~lgnal with the luminance slgnal by placlng the chro~inanc~
information at odd multiples of on~-half the llnQ
frequency, Thi~ was possiblQ becaus~ the scannlng o ratea ~or the chromlnanc~ signal and lumlnanc~ ~lgnal are the ~a~e (approxiroately 15.734 l~z). Intorl~avlng o~ the chro~in~nce signals i~ 8hown ln ~lgur~ 2 at th~
453rd harmonic 36 of half the llne frequency 27, a~
well as at the 455th harmonic 38, 457th har~onlc 40, and 459th harmonic 42. Those ~killed in th~ art wlll r~cognize that luminance and c~rominance ~lgnal ~nergy will continue along the frequency ~pectrum at harmonics above tho~e ~hown ln Flgur~ 2.
The intent of ~he precent lnventlon 1~ to provide digital audio in the ~ound carrier of a standard teleY$sion signal in ~uch a manner t~at the audio signals will not interfere with the video portion~ of the television ~ignal, thereby providing compatlbility with the video processlng stages of standard5 ' television recsivers. In order to do this, the digital audio signals are synchronized with th~
horizontal line frequency so that ~he harmonlcs o~ the ~odulated audlo ~ignals will appear iQ regl3tration with the ~uminance portion of the televiæion ~ignal 1 32g9 1 7 frequency spectrum. Thus, the digital audio signals will be interleaved with the color signals and will not interfere with the color reproduction in a video program.
In order to accomplish the objective~ of the present invention, the stereo left, stereo right, and SAP audio channels are time division multiplexed on the 4.5 MHz audio carrier of a standard televlsion signal USing comblned multi-phase modulatlon and AM modulation. The 4.5 MHz intercarrier is phase locked to the video horizontal scan rate of 15.734 KHz. In the preferred embodiment, the audio signals are digitized using adaptive delta modulation ("ADM") techniques and particulary, the ADM system proposed by Dolby Laboratories in a paper entitled "Recent Developments in Digital Audio Techni~ues", K. J. Gundry, D.
P. Robinson, and C. C. Todd, Dolby Laboratories, San Francisco and London, presented at the 1984 NCTA Show. An integrated circuit chip for providing Dolby ADM decoding is available from Signetics Corporation under Model No. NE5240.
Also pertinent is a paper entitled "Digital Audio for Cable Television", Clyde Robins, NCTA Technical Papers, March 15-18, 1986.
The adaptive delta modulation audio sampling rate used in digitizing the audio data in the preferred embodiment of the present invention is an integer 1 32~q 1 7 factor of the intercarri~r frequency. Three dlgltal component~ are establ~shed for each dlgltlzed channel ln the Do~by ADM techniqu~. These are ~mplitude lnformation, frequency ~ompandlng dae~, and a~plltud~
compandlng data. ~n the best mode e~bodlm~nt, th~
digitized audio 1~ trans~ltted vla multi-phas~
modulation on the aural carri~r. Forty-four bits of datA ar~ transmitted ln each horlzontal llne. The fir~t four bit~ are u3ed as a prea~bl~ for blt ~ynchronlzation. The~preamble 18 tran~ltt~d ~lth a unique pha~e and a~plitude, identlfying lt ~8 a ~ynchronizatlon symbol.
A~ noted above, three channel~ of d~gital audio are preferably tran~mltted; nam~ly, ~tereo l~ft, stereo right, and ~econd ~udio progra~ channel3. The left ~nd right ster~o channel~ each requ~re.13 blt. of diqitized (ADM1 data for each horizontal lina of v~d~o in the t~le~i~ion signal, and one b~t per chann~l per line for frequency and amplitude companding data. Th~
SAP channel requires ll bits of digitized audio dat~
per horizontal line and one bit per line for frequency and amplitude companding data. This bit di~tribution i~ summarized ~n Table l.

'`

1 32~9 1 7 AUDIO DATA FRAME

Number of Bits Bits _ Data _ 13 0-12 left audio 1 13 left audio companding 13 14-26 right audio 1 27 right audio companding 11 28-38 SAP audio 1 39 SAP audio companding 40 bits total The horizontal scan rate ("fH") in a conventional NTSC color television signal is 15.734264 KHz. The audio intercarrier is 286 times the horizontal scan rate, or 4.5000 MHz.
Factors of the audio intercarrier are 2, 11, and 13 (2 x 11 x 13 = 286). Thus, as noted above, the adaptive delta modulation audio sampling rates work out to be integer factors of the intercarrier frequency.
The modulation rate of the multi-phase modulated audio data is 22 x fH, which provides 22 "symbol times" per horizontal line. Thus, there will be 13 intercarrier cycles per symbol time (13 x 22 = 286). The multi-phase modulation provides two bits of data per symbol, which results in the transmission of 44 audio data bits in each horizontal line. This translates to a bit rate of 692.3 kilobits per sec~nd -~ BPS~). U~lng non-return to zero ~NRZ~) coding mak~ ~he maxlmum~8ymbol transltlon rato one-~lalf Of the ~ymbol rate or ll fH. ~he t~yqui3t required bandwldth lg +~- 173.07 ~Hz, In accordance wi~h the b~t distrl~utlon for the audio dat~ shown in Table 1, the stereo ~udlo d~lta mod~lation ~ampllng rate for each of the l~ft ~nd right channels ln th~ preferred embodl~ent 1~ 13 f~.
Th~ se~ond aud~o progr~m d~lta modul~tlon ~a~pl~ng rate 1~ 11 f~. Finally, the adapt~ve co~pandlng ~a~pllng rat~ ~8 one-half f~. In t~o D~lby ADM
~y~t~r~, both amplltude and frequency compandlng data are used. ~n the pre3ent lmplementation of Dolby ADM, the companding bits provided in each horizontal line are alternated between amplitude data and frequency data. Each llne contalns either a~plltude.or frequency companding data, and the contents of sequ~ntial lines alternate from one line to the next.
Thu~, the adaptiv~ compandlng sampling rate for each type of companding data can be half the hori20ntal 8can rate.
The audio data is carried by the aural intercarrier of a television signal using multi-phase modulation. The same carrier uses AM modulat~on ~or vldeo vertical and horizontal framing, a~ w~ll a~ the audio carrier phase reference, and audio data bi~ time and frame reference. When the p~e ent invention i5 u~ed in connection wlth a cable televl~ion 8y~te~, program identif ication~ a;ld decryption ~eeds are also 1 32~9 1 7 carrled on the aural lntercarrler using AM modulation.
In t~e cable t~levlslOn ~nvironment~ lt 18 advantageous to encrypt the aud~o d~ta~ and the co~po~lte data stream ~y b~ serlally ~n~rypt~d ~0 that only authorized subscrlber~ ~111 ~e ablo to racover and r~produc~ the dlgltal audlo progra~lng.
In a cable televi~ion ~ystem~ dlgital ~udlo ~ay be transmitted ln ~ccordanc~ wlth the pre3ent inventlon along wlth a vid~o signl~l th~t 18 Bcr~bl~d us~ng, e.g., conventio~al 6/10 db dyna~lc ~ync ~uppr~lon technlques ~nd~or vld~o in~er~ion scrambllng sy~te~s. Those skilled ln the art ~re well awar~ of the~e and other ~crambllng ~yste~s~ Wh~n using ~ync ~uppression ~cra~bling, the ti~ing reco~ery ~ignals sent a~ AM on the ~ound carrlar may be offset ln tl~ from t~e video, increaslng the secur~ty of t~e video ~ign~l, wh~le making the ~ound unrecoverablo by unauthorlzed boxes.
. The AM modulated data ln the slgn~l trans~itted from the cable televl~ion headend to sub~crlber converters contains 16 bit~ of data for 6/10 db sync suppres~ion ~crambling selection, program ~peclfic data such as price, morality rating, and like data as well known in the art. An example of a prior art headend controller which tran~mlt~ ~uc~ data ls t~e model AH-4 controll~r manufactured and sold by the Jerrold Divigion of General ~n~tru~ent Corporatlon.
In accordance with thfi preferred embodlment of th~ pre~en~ inventlon, '3 new bit8 of data are 16 1 32 8ql 7 appended to the AM data tag to carry seedlng and kcy data for the decryptor, servlce COJQ data for tho dlgltal audio converter, and tlm~ shlft de~cra~bllng data. Thi~ data 1~ ne~Q~sary to enabl~ an authorls~
d~gltal audio convert~r to rec~iv~, decrypt, and reproduc0 80und from the dig~tal audlo ~lgna 18 tran~itted wlth the tel~vi~lon signal. A ~Qrvicc code can ~180 be prov~ded ln the data that will bQ
read by non-dlgital ~udlo converter~ to deauthorlz~
them 80 that they c~n~t rec~iv~ any tel~vl~lon progrAm c~Dnnol~ carrying digltal ~ound.
When the pre ent lnventlon i~ u~ed ln con~unction with ~ cable televlsion ~y~tem, thre~ prlmary co~ponent~ are u~ed. T~ese ar~ the addre~able con~roll~r ~al80 referred to a~ ~headend controllerR), ~he headend ~ncoder, and the sub~crlber converter (al80 known a~ th~ ~subscrlber termlnal~). Both the addre~able controll~r and encod~r are pre~en~ a~ the headend from which the cable tclevl~lon ~ignals ~re sent by the cable sys~e~ op~r~tor. T~e addres~able controllsr controls all 3ubscriber termlnal~ in th~
cable television sy~tem, controls the encoders/decoder~ assoc~ated with the system, configures ~crambling modes, service codes~ and encryption keys, and orche~trate eh~ dis~emlnatlon of all decryptlon keys. The encoder of the present ~nvention 1~ ~ headend ~evice con~isting of a number of ~ubcomponent~ including an audio dlgiti~er, ~ld~o scrambler, tag .nsertlon logic, addressabl~ controller interface logic, and modulator circuitry. These components are described below in connection with the description of Figure 3.
The subscriber converter is a device located at each subscriber's residence and contains an RF
converter module, demodulator, addressable controller interface logic, subscriber interface logic, audio decryptor and digital to analog t"D/A") converter, together with a video descrambler and modulator. Each of these elements will be described below in connection with the description of Figure 5.
In addition to the AM data path, certain data is transmitted over an FM data path from the cable television headend controller to the subscriber converters. This data is typically modulated using frequency-shift keying ("FSK") techniques well known in the art. The model AH-4 addressable controller referred to above is an example of a prior art 2Q headend controller which controls data which is both AM modulated for certain tagging data and FSK
modulated for encryption data, authorization codes, and the like.
I Table 2 lists various terms and their definitions which are used herein in connection with the description of the transmission of data from the headend controller to the encoder and subscriber converters in accordance with the preferred embodiment o~ the present invention.

la 1 328q ~ 7 TA~ W 2 AUDIO DECRYPTION ~EYS Set of 8 nlbble~
transmitted ovar t~e FM
~FSK) data path to t~e subscrlber term~nal ~converter) and encodor.
The nlbble~ ~re used to se~d the cryptor~ in the headend encoder and subscrlber tar~inal decod~r. At ~ny one ti~
four of the nibbles ar~ ln u8e. The unu~ed nibble~
~ay be changod out ~h~le ~dle. Data id~nt~fy~ng the four nlbb1e~ to be used, and the order of usag~ 1~ trans~ittod fro~
the headend control1er to ~ the encod~r, and tran~mitt~d ~rom thc encoder to the sub~criber terminal as AM ~odulated tag data.

KEY USAGE SPEC Speciies which of the audio decryption key~ to u~e ln each of the 4 nibb1e slots ln the subscr~ber ter~nal de~cra~bl~r circuit. Any of the 8 keys can be 1 32~9 1 7 a~ lgnQd to any of the 4 slot~. Tl)l~ a~lgn~ent daea 18 sent 1-. blt~ 16-2 of tho AM tag, and ~pecll~l~ to eacll televlelon prograD~.
.

T~G DECRYPTION l~Y ~ blt nlbble ~ent from the headend controll~r ~o th~
~ubwrlbor t~rnlnal ov~r tho ~M dat~ ~ath. Thl~
key is u~ed to decrypt th~
encrypted ~erv lc~ code ~r.d encrypted ~eed thae 1~
sent in th~ AM tag. Two lS tag decryptlon ~ey~ exist ln th~ sy~te~o, but only on~ l~ ln u~e at any tlloe.
A key ~ay be changed out when it 1~ n~st in u~.
The key that i8 to be used to decrypt the tag ~s specif ied ln the tag .

VIDEQ SERVICE CODE Servic~ cod~ ~ent ln bit~
0-7 of the AM tag, and used to deterraino authoriz~t~on for the video portion of the 1 3~89 1 7 program. A ~ub3crlber ter~lnal not authorized for tbl~ ~ervlce co~e will dls~llow v~ewlng of the vldeo port~on of th~
progra~o, A non-digit~l audio ~ub~crlber tarmlnal will al80 uao lt to allo~
or dl~allow view lng (non-lo , dlgltal ~u~io convereor~
~hould always b~
deauthorized for dlgit~l audio servlces ) .

AUDIO S~RVICE CODE Servlce code of t~ audlo portlon of th~ progra~, ~ent in an encrypt~d form, decrypted by tag decryption key. The audio service code ls one of the field~ of data sent ln bits 16-23 of the AM tag.
This service code i9 used by the digital audio converter to deter~in~
authorization for 3tereo audio. If the upper tag bits ars not pr~9ent~ the standard ~ervice COJ.d .. . ~ .. _ , . .
; :, 1 ~289 1 7 (blt~ 0-7) ar~ u8ed for authorlzl~tlon v~lidation, ~nd au~io ls tran~mitted ln the standard T~ fomlat .

TIME SHIPT SPEC Dat~- speclfying tl-e m~gnltude of the t~me ~hl~t bet~te~n tho t~lng pulses on the ~ound carrier AM and the ~ync po~itlon ln t~ vldeo.
Tho tlme h~ft ~pec 18 televislon program specif lc, and sent In bits 16-23 of the tag in an encrypted format u~lng the tag decryption key for recov~ry. Tlm~ shiftinq of the t2~g can be used in a static mode only, and can change only during program changes ~an audio hit will occur when the change takes place ) .

DECRYPTION SEED 8 bit ~eed sent in bit8 25 ' 16-23 of the AM tag, used to seed the audlo decryptlon s:ircuitry.

~' " .
' .

~ 32~q 1 7 The seed i8 progra~
8p~clf iC and can change on ~ dyna~lc b~sl~. ~ new seed lo put lnto use ln accordance with th~ tialng e~ abllshed by d~ta ln th~
AM ~ag. The see~ ent in an encrypt~d form~t using the tag de~ryptlon key for recovery.

Data communicat~d over the FM path between t~e headend controller and th~ ensoder includes a ~lgnature u~ed to protect ~enaitlve lnformation communicated over the p~th, tag and audio ~ncryption key~, key u~ago ldentlfiers, scra~bling ~ode dat~
lncluding 8ync suppresslon ~od~ and ti~o ~hlft specif ications, the vldeo and audlo serYlc~s cod~, ~nd price and morality ratlng data. Dat~ whlch pertains to the digital audio servlce and is ~ent to the ~ubscriber termlnal over the FM path includes a ~ignature used to protect sen~itive information communieated over the path, tag and audio decryption key~, and authorlzation lnfor~ation.
Data sent from the encoder to the subscriber terminal over th~ AM data path includes ~ideo and audio sRrvice codes, ~crambl~ng mode and ti~ing infor~ation tincluding ~ync ~uppra~sion mode and ~ime .~ .
..

shlft sp~clfi~ation), kcy u~age speclflcatlons, th~
decryptlon 6e~d, and prlc~ and morallty rating data.
Data transmltted ln thQ ~M tag can be ~ent ln ~n encrypted ~ormat~ requ~rlng th~ corr~ct tag d~cry~tlon key ln the termin~l to prop~rly interprot tbe data.
Turning now to ~lgur~ 3, a headend sultable for - U~8 in transmlttlng dlglt~l audlo signal~ ov~r a cab~
t~l~vi~ion network ln àccordance wlth the present lnventlon 18 ~hown ln block dlagram for~. a headend controllar 50, ~uc~ ~ th~ Jerrold AH-4 ~ontroll~r, ~nds varlou~ dat~ including control d~t~, ~ncryptlon key~ ~nd ~eed~ to a loicroprocessor 52. Data to b~
tran~mitted on the FM data path i8 output at termlnal ~A~ ~o an FM modulator 104 in a conventlonal manner.
Left, right, and SAP audio channels ar~ lnput to ~n ~daptlve d~lta ~odulator 5~ whlch digltl~s. tho input audio informatlon and outputs it in parallol for~t to a par~ l to ~rial 1O91C clrcuit 56. Clrcuit 56 can compri~e any of the w~ known parallol to ~crial data translatlon technique~ well known in the ~rt. ~or example, the right, left, and SAP data fro~ adaptive delta modulator 54 can be loaded into shift regi~ters (a separate 13 bit shift register for each of the right and left channel data and an 11 bit shif~
2s rsgister for the SAP channel d~t~), and th~n th~
outputs of the three ~hift regi~ters can be lnput.to a parall~l load ~hlft regi~t0r to provide ~ ~erlal output. The right, left and SAP comp~nding bit~ fro~

~. .

2~ ~ 3~9 1 7 modulator 54 can be loadod lnto the par~llol load ~hlft reglster vla lndivldu~l fllp-flopo.
Variou~ tlmlng ~lgnals to controi adaptl~o delta modulator 54 and parallal to ~erlal ~ogi~ 56 ar~
provlded by tlmlng logic 68. Tlmlng loglc 68- 18 driven by an 18 MHz voltage controlled o~clll~tor ~VCO~ 70 and the ~orlzontal synchronlzatlon ~lsas from ~ync Qeparator ao after a ph~a~ ft pro~lded by delay 84. Timing pul~ at a ~r~quency o 13 f~ Ifor thQ lQft and rlght ch~nnel ~ampllng rat~), 11 f~ ~for the SAP 8a~pl1ng r~te), ~nd fH/2 (for th~ adaptlvo co~pandlng sampl1ng rat~) are lnput to adaptlv~ d~lta ~odulator 5~. Thc horlzontal scan ratQ frequency f~
1~ ~nput direc~ly to parallal to ~rlal log1c 56 togeth~r with a timing s1gnal at a fre~uency of 44 f~
whlch provide~ the de~ired blt rat~ of ~4 ~lts per hori20ntal lln~ (i.o., 692.3 RBPS). This ~a~e ~lgnal i~ al~o lnput to an encryptor 58 ~hich 1~ used to encrypt the digltal audio d2ta output fro~ parall~l to serlal logic 56 a~ well as the control and tagging data whlch i~ input to encryptor 58 from headend controller 50 via ~icroprocessor 52.
The digital audio data, prior to transmission, iQ
encrypted by encryp~or 5~ using the hardware ~hown in block diagram form in Figure 9. Tha s~m~ h~rdware 18 used for both encryp~ion and decryption.
Re~errlng to Figure 9, a 1~ blt k~y i~ loaded fro~ the ~icroprocessor vi~ d~ta bus 272 to a 16 bit ~tey latch 276. Addre~s ~ecode log~c 270 i~ used by 2s 1 32~9 1 7 microproces~or 52 to ~ddress latch 276 as well a~ th~
varloua other l~tchs~ contalned ln the cryptor hardware of ~igure 9. The loaded 16 blt key 1~ u8ed to lnitlallze ~ ~et of sh~ft reglster~ 278, 280, ænd 282 at th~ beg~nnlng of oach vldco field. TJ~e ~hift registers rotate on a blt t~ming b~a~, on~ shlft p~r blt .
~ ~eparate 8 bit seed i8 trans~itted ln the Al~
tag data, decrypted, and loaded lnto an 8 bit seed l;~tch 27~ via data bu's 272. At the beglnning o~ ~oh v~d~o f l~tld, ~h~ cont~nt8 o~ the ~ed regl~t~sr 2~
loaded ~nto an 8 blt ~seed~ sh~ft reglster 286. A blt .mixer 284 cooblne~ the outputs of th~ key ~hift regi~ter~ 278, 280, and 282 to produc0 f~ve control s~gnal for the non-llnear sequential logic circu~try 288. Th~ loglc proces~es data frolo tbe blt mix9r 284 and the se~d ~hif t rQg ister 286 to produc~ a ~lnglo blt ~tream, whl~h 18 exclu~$~e OR~d by an ex~ uslv~ OR .
gata 290 w~h ~h~ carryout of the seed ~hift rsglster ~o produce the crypelon bit stream. The cryption blt ~tream is 8hift~d baek lnto the serial lnput of the qeed shift register 286. A data signal ~which may be either encrypted or clear~ i~ lnput at ter~inal 294 where it is exclu~ive ORed at qate 292 with the cryptlon blt stream to produce a data output (~ither decrypted or encrypted) at term$nal 296. Thus, any d~t~ signal lnput at terminal 29~ i~ converted from encrypted to clear, or vlce Yersa, ~nd output on terminal 296 by excluslve OXing it with the eryptlon 1 ~289 1 7 bit stream.
The preferred embodlment of the digltDl audio syste~ contalns ~gh~ cryptlon key nlbble~.
Each nlbble h~s four bit~. At any on~ tlme, on any of the left, right, or SAP audio chann~l~, only ~ou~
nibblo3 are ln us~. The other four nibbles ~ay be changed while out of s~rv~ce.
Encryptlon keys ~re dl~tribu~ed over th~ PM d~t~
path. They aro transmltted ln an cncodsd for~t, and arQ decoded in the subscrlber ter~inal u~lng a dscoding algorithm based on th~ ter~nal ~lgnatur~
whiCh 1- do~nloadad durlng lnitlalisatlon of th~
ter~inal. Th~ key~ ar~ ~tor~d ln nonvolatile ~e~ory in the encoded format for further protectlon. ~ 11st of key~ ~8 period~cally tran~m~tted o~er the FM dat~
path for dissemination as de~cribed below.
A descr~ptor in the AM tag dat~ indlca~es whlch four key~ to u~, and in which co~blnation to ~ffec~
decryption of the audio data. Two bytes of data ar~
used to de~cribe the key usage. Th~ two byte~ ar~
broken into four nibble~, each specifylng th~ key to be used in a partlcular nibble of the key regist~r.
T~u~, four key nibble~ can be used in any order to lniti31ize the k~y regi~ter. Thc least ~ignificant nibble of ~he fir3t key usage byt~ specifie~ the appropriate key nibbl~ (0-7) to use in key latch bits A-D shown ln Flgure 9. Th~ mo~t ~ignifican~ nibble of the f~rst k~y usage byte specifies the key nibble for key l~tch bit8 E~. The l~st ~lgnlficant nibble of the second ke~ u~age byte pecifi~ th~ key nlbble for . ' ` ; ' ' 2~ 1 32~q 1 7 k~y latch blt~ J-M. The most slgnif lcant nlbbl~ of the second k~y u~age byto speclf 1~8 thQ key nlbbl~ for key latch bit8 N-R.
~he encryptlon seed 1~ tl~e sQcond plece o s infor~atlon regulred to d~crypt th~ aud~o data. Th~
seed 1~ a random ~lght blt data byte orlgln~tad at tbo ~ c~ble televl~lon head~nd and tran~ltted in the AM tag d~t~ ln ~n encrypted format. Tho seod 1~ decrypt~d uslng th~ tag decryption key speclf lQd ln the Ul eag.
0 She s~ed 1~ load~d ln~o ~h0 cryptor hardwaro ~E~igur~
9) ~nd usod to lnitlaliz~ th~ ~aquentlal loglc 288 of th~ cryptor ~ardware (~la gate~ 287, 289) at tho beg~nnlng of each f iold of ~udio lnfor~ation.
Two le~els of synchronizatlon b~tween the encryptor and decryptor ~u~e be met for ~rror fr~
data recovory. Fir~t, the ~equ~ntlal loglc. of th~
encryptor and decryptor ~u t bc ~ynchronlzed do~n to the bie l~el. Socond, c~anges ln k0y and ~d infor~atlon must be synchronized down to the field le~el.
The cryptor hardware of Figur~ 9 18 lnitialized on the leading edge of the fir~t horizontal ~ynchronization pulse transmitted on the aural carrler amplitude modulation. Ini~iallzation 1~ accomplished 2s by transferring key data from tho holdlng latch~ 276 to the shift regi~tars 278, 280, and 282, from th~
seed holding latc3~ 274 to its ~hift regl~ter 286, and by initlali~ing the sequential logic 288 to ttl~
inltial 8t~te8 spec:if ied by the k~y. Su~,s~quent ~Qd ans~ key chan5~e8 occur based on B countdown ~ch~m~ by audio fisld. Th~so chang~ take placo during th~ 8 f i~ld as ~ynC ~uppre~810n ~ ch~nqe8. The ~countdown~ fleld of tho AM t~g 1~ de~crlbcd belo~.
~ha ~eod and key ~re loaded lnto thelr rc~pectivo holding latchc~ 274, 276 up to one fleld in ~d~nco of th~ transfer ti~e, ~nd the ~rd~re handles tho eran~fer during field ~ynchronlzation.
A 13 blt ~xton~lon eo tho st~n~ard 16 bit AM t~g u~d ln tha Jerrold A~-4 he~d~nd controllor provl~o~
transport data r~l~t~d to dlgltal audlo. ~ata 18 30nt ~mplitud~ modulated on t~e ~V ~ound carrler, lnter~persed with th~ synchronizatïon recovery tlalng information. The A~ data contain~ tl~ing pulse~
~ynchronized to the suppressed horizontal ~ync pul~e~
of the scra~bled video, as well a# dat~ ~ul-o~ for ~ignal t~gglng and descrambling sp~clficaeion~. Ths entlre AM pul3e train ~y ~ tim~ shlfted fro~ th~
assoclat~d vldeo progra~.
Details of the timing of data ln the A~ pulse train are shown in diagrammatic form ~n Figures 10 and 11. Timing pulses are abs~nt during the vertical interval portion of the television signal, and ~he flrst horizontal synchronization pul~e present on the AM ~ignal correspond~ to llne 22 of th~ vid~o field.
Horizontal sync pulses 302 are deplcted in t~e pul~
strea~ 300 oÇ ~igure 10. Thes~ pulses ar~ 63 ~3~917 ~n~croseconds apart. ~orizontal lines ~re lndlcated ln the tl~alng d~agram 310 cf ~lguro 11 by solld ~lne~
316 .
A timlng pulse occur~ ~or aach horlzontal lln~.
Dur~nq llnes 22-S3, tag data pulses may occur 2 ~icrosecon~ after th~ hor~zontal sync tlmlng r~ference. Durlng lin~ 22, a da~:a pu1~4 ~~tart bit~) 312 alw~y~ occur~, slgnlfylng the start of a data fra~. Du~lng llnes 23-53, th~ presenc~ or ab~encQ of a pulse 3~ represont~ a one or a zero in blt~ 0-~0, respec~iv~ly, of th~ AM t~g.
T~bl~ 3 break~ down the component data fi~lds of the AM tag~

TaBLE 3 E~ITS IELD DE~INITION

O - 7 Video servlc~ code 8 - 11 Scrambl lng mode com~and 12 - 15 Scrambling mode countdown 16 - 23 Digital audlo encryptlon data 24 - 27 Digital audio data descrlptor 28 - 39 Companding data id~ntif ~er slts O-lS of the AM tag dat~ r~lato to th~ vid~o scra~bling of the telo~i810n ~ignal and thelr u8~ i~
conventional and ~ell known ln th~ Art. The vldeo ~er~lce codo flold contalns a cod~ used to detar~ine S authorizatlon for tho ~ldeo portlon of t~ cabl~
television program. Any non-dlglt~l au~lo ~uhsGriber terminal ~e.g., those converters Dlro~dy ln t~o ~lel~) w~ll be deauthorlzed for dlgit~l ~udio vidso program~lng, and vlewlng of such progr~m~ ~111 b-dis~llowed bas~d on ~he ~ervice cod~ tran~lttod ln bits 0-7.

, . . .

1328~17 B~t 28-30 of the tag d~t~ lndicate w~ethor line 54 of th~ current vldeo fleld co~talns ~mplltudo or frequency compand~ng data. Thig ls nece~sary b~cauae odd fields conealn one ~ore l~n~ than oven ~olds, And ln accordanc~ wlth the pre~ent lnvent~on, the compandlng dat~ alternates between freque~cy ~nd amplitude d~ea ev~ry f~eld. Thus, ~ co~panding b~t in any giv~n llne alternates between anplltude and frequsncy ev~ry two fl~lds. Th~ ~tate of blts 28-30 ~rv0 to ~ync~ronl~e Ithe trans~iteer ~nd rec~lv~r ~lth r~spact to eb~se two p~ra~eters. T~r~ b~t~ are u~od to ~llow for noi~ im~unlty through redund~ncy. If t~o or mor~ of th~ thre~ bits ar~ zero, line 5~
contalns a~plitudQ data. If t~o or ~ore of tha threo bit3 are Qet, llne 54 contaln~ frequency compand~ng data. Each line contaln~ ~ith~r a~plitud~ or fr~quency co~pand~ng data, and th~ content~ of s~quantial line~ alternate from one lin~ to t)~c nbxt.
Bits 16-23 of the tag data carry data agsociated with the digltal audio proqram, and i~ not receiv~d by non-digital audio ~ubscriber terminals. Data ln th~
digital audio da~a field is multlplexed, and the contents of a particular rame i8 spec1f ied by th~
value in the ~digital audio data descriptor f ield~, contained ln bits 2~-27. Table ~ dsf ines tl~e correspondence between ~he data descriptor f ~eld and the data f leld.

~2 1 32~9 1 7 TABL~ 4 Dat~ Descrlpto~ Data Fl~ld ~lts 24-27 Blt~ 16-23 _1111 Audio Service Codo (encrypt~d) ll~O Audio D~cryptlon S~ed (~ncrypt~d) 1101 ~ey U~go Sp~c byt~ ncrypted) 1100 ltey U~ag~ Spec byt~ 2 ~encrypt~d) 1011 ~me Shif t ~pcc ~sncryptod ) . lO10 Spar~ 1 1001 Checkbyto (clear; previou~ 7 fl~
1000 Tag Decryptlon l~ey spnclf ier ~clear) Olll Audlo Service Code ~encrypted) 0110 Audlo Decryption Seed (encrypt~d) OlOl ~ey Usage Spec byte 1 (en~rypted) 0100 ~ey U~age Spoc byt~ 2 ~oncry~tod) 0011 Tlmo Shift Spoc ~encryptod) OOlO Spare 2 OOOl Che~kbyt~ (clears prevlous 7 fl~ld~) O000 Tag D~crypti3n Itey ~pecif ler ( clear) The data descriptor f ield al~o has tho functlon of ~peclfying when to put a ne~ decryptlon key, se~d, and ti~e shlf t ~pccif lcation lnto usa. Data f lelds are ~ent ~ n a ~equentlally descendlnq or~or. When t~e data d2scriptor field reaches OOOl, the new ~values aro loaded ln~o l:~e decryption circuitry latcbe~" i.e., ~' , ' -..

~1 ` 13289l7 ~esd l~ch 27~ and key latch 276 of Flguro 9. When the data de~riptor fl~ld reachQ~ 0000, th0 newly loaded v~lues are put lnto u~e. The coun~down f leld used for video de~cr~mbl1ng tl~lng 1~ l~pl~ented in th~ same ~ay, and 18 coordlnat~d 8UCtl that vld~o mod~
changes occur during the ~ame fl~ld as audlo par~met~r cl~an~o~ .
Wh~n d~crypting th~ content~ o~ the audlo dat~
f leld, ono of two tag decryptlon koy~ ~r~ u~od. Th~
on~ actually u~od i~ the on~ loost recently ~peclf l~d ln ~quencs. Sn othor ~rords, when docryptlng ~udlo data fleld~ 15~ h~ tag decryption k~y sp~clflod in f leld zero 1~ u~d. Wh~n decryptlng audio data f i~lds ~-2, ~he tag decryption k~y ~peclfi~d in fi~ld ei~ht 1~ uæed.
An audlo control byte cont~ins contro~ p~r~meters u~ed to properly decode the digltal audio progr~, an~
~elect the proper ch~nnelæ. Shi~ byt~ 0nt in tho clear (unencrypted) aæ part of th~ ~M tag ~nd bas tt~e forn~at ~hown ln Table 5.

TABI.E S

BIT DESCRIPT~ON

0 Tag key ldentlf ler 0 ~ Tag decryption key 1 1 - Tag decrypt lon key 2 SAP avallabl~
0 ~ not av~llable 1 ~ sYallable 2 Program Audlo on SAP
0 - Progra~ audio on L~ ~hannoln 1 ~ Program audic~ on SAP channel

3 Not u8ed

4 Not u~ed Not used 6 Not u~ed 7 Not used In order to allow change out of the tag decryption k~y wlthout di~turbing the operation of t)le ~ysten~, two keys exist. ~t any one tilD~ only one key l8 ln u~e, whlle the other key i~ ~y~tema~1~ally changed out in hll ~ubscrlb~r terloinal~. Th~
decryption k~y currently ~n u~e i8 ~pecif l~d in the tag k~y ldentlfl~r f131d. The SAP availabl~ ~lag lndicates the presenco or absence o~ ~AP progra~
materlal, The 2program audlo on S~P chann~l~ flag spec~fies whlch channol t~e progra~ audlo re~ld~s ons s i.~., the ~ono chann~l, or t~ at~reo channol~.
Tbe audlo 8ervlcR coJe d~ta fl~ld indlcate~ the proqra~ tier, and i~ u~ed to deter~ authorlzatlon statu~ for th~ audlo portlon of a tunod d~gltal aud~o progra~. ~he audlo ~er~ic~ cod~ 8~nt ~n tho audlo d~t~ field 1~ ~ncryp~ed and ~u~t be docrypted prlor to ~valuatlon. Th~ tag d~ryptlon koy to b~ us~d 1J
~pecifi~d ln the a~soci~t~d fl~ld of audlo dat~ by U8Q
of the ~ag key id~ntif ier de3cr~bed abovo.
~wo byt~s of dat~ ~p~cify the k~y usagQ for audio decryption. These field~ are sent in an encryp~d forloat, and mu~t decrypt~d using tho appro~rl~te tag d~cryption key prlor to evalu~tlon. The two byteB ~r~
broken down into four nibble~, e~ch speclfying th~
appropriate key nibble to be used ln ths ~s~oc1ated key section. Table 6 indicates the correspon~ence-between the key usage identifler nibbl~s and the key nibbles.

TAE~LE 6 BYT~ BITS CORRESPONDING~ Y S~CTION

0-3 ItQY l~tch bit~ A-D
4-7 I~y latch blt~
2 0-3 ~y latch bits J-~
2 ~-7 Rey latch bit~ ~4-a Thi~ scheme allow~ any key nibbl~ to bo used ln any ~ect ion o th~ k~y latcl~.
Another byte of data i8 u~ed for seedlng tha audio decryption hardware. Tl e audlo dscryption seed i8 ~ent ln an encrypted forla~t, and 1~ dec~ypted u~lng the appropriate tag decryptlon k~y. It 1~ put lnto u~ ~hcn the countdo~n reache~ z~ro.
~he tl~e ~hift speclflcatlon byto indlcatQ~ th~
lS le~d time betw~en the AM horizontal sync pulse and the appropriate ~ynchronization in~oc~ion point ~n the video. The time shift speclfication 18 ~tatic during ~ t~levislon program, but may change ~ith each program ctlang~. A new tlme ~hift ~pecifica~lon i8 put into ~f fect when the ~ountdown reaches zero. The ti~e ~hlft speclfication ~yta i~ ~ent in ~n encrypted for~at and i~ d~crypted us~ng the appropriat~ tag decrypt ion key.

37 1 328q 1 7 The tlm~ shlft 1~ c~libr~ted, for exa~le, ln 1.8 ~icrosecond incrementA, where a ~peclflcatlon of ~ero repr0~ent8 no ti~Do shi~t ~ ln all non-digltal ~udlo sync suppres~iQn channels), ~Ind a ono r~present~
s 81l1ft of 1.8 atlcrosecon~s lndicatlng tho requlred delay at tl~e tar~oinal between r~c~ptlon of ttle A~
~ tim~ng pul~e and ~n~ection of the ~ynchron~ation pul~e in th~ vldeo. Tho ~ximu~ allowabl~ tl~e ~hift i8 16 lncreD~entr.
The ~heck byte d~ta 18 an Qlgbt bit v~lu~ hlch, when 4um~0~d (MODULO 256) ~i~ h~ pr~c0dlng ~ sn byte~ ~a~ ~ent over ~h~ AH t~g, ~ncrypted or not) total~ zero. The ~un~r~lng proces~ i8 dono uslng data a~ 3ent over the AM ta~, prlor to d~cryption. Prior to using any data sent ln the audlo d~ta f ield, v~lld check byte must be verif l~d.
As ~lready noted, certain fra~ of t~e audio data ~ield are ~ent ln an encryptod format u~lng ~ tag encryption key. Two tag encryptlon key~ exlst ln th~
sy~tar~. At any one tim~, only one i8 ln u3e. Th~
other key, while not ln use, may be changed out on a terminal by terminal basis by addre3~1ng ~pecific terminal~ over the FH data pat~. The key to be used to decrypt the tag da~a ig specif ied by the tag key identif ier a~ ds~cribed abo~.
When tran~itting ~ ~ey to a ter~inal over the FM
~ata path, th~ headend controll~r en~o~e~ the key ith the ~ubscriber ~ermlnal signature. Th~ sub~criber 3~ ~328917 terminal, prlor to us~ng the tag decryptlon key, decodes lt using lts signAture as dQscrlbed below.
The encryptlng and decrypting of t~g data d~ r~d over th~ AM ~ ul~ted sound carrler data path ~ill no~ be de~cribed. In order ~o psrfor encryption and d~cryptlon, a bit s~t ln th~ ~ecryptlon ~ key indicates that t~e as~ociatod operatlon should b~
psr~ormed. A cle~r bit indicatQs t~e operaelon ~ould b~ lgnored. ~lt zero i~ tho le~st ~ignlflcant blt of lo the encryption key. ~abl~ 7 lllustr~t~s th~ s~quonc0 of operatlons to be perfor~d by encryp~or 58 ~riguro 3) to encrypt a byte of d~t~ for tr~n~r 18sion over the AM pa th.

TABL~ 7 BIT OP~TION
-0 Swap bi ts 0 and S
Swap bi ts 2 and 6 2 Rotate byte left one po~i~ion w/o carry 3 Decrem~nt byte by 1 without carry , 39 132~9~ 7 T~ble 8 lllustrate~ the ~equ~nc~ of oper~tlon~ to be performed in order to decrypt a byte of d~t~.

TAelLE B

~ sIs OPERATIO~

S 3 Incre~ent byt~ by 1 wlthout carry 2 Rotat~ byte rlg~t on~ poslt~on ~/o c~rry 1 Swap bit~ 2 ~nd 6 O Swap bit~ O and 5 ~ an ~dditional measure of ~ldeo security for tbe ~ynchronization ~uppr~sslon ~cra~bllng, t~
digl al audio syste~ o~ the present in~ention ~llo~
timo shlft between the sync recovery pulQe~ on t~e ~ound carrler and the actu~l sync positlon ln tbe video signal. Th~3 ~cheme causes ~ny appar2tu3 ~hlch is currently available to ~ub~ceibers for defeating Qync suppres~ion to re~ult ln a telovision picture with incorract horizontal reglstratlon, resultlng ~n line down the ~lddle o~ the televi~ion picturo. The ~ime between ~he sync recovery pul~e~ ~hlch ar~ A~
modulated on the sound carrier and t~e vidso synchronlzatlon ~ay be ad~ust~ fro~ zero tv 28.8 micros3conds ln increment~ of 1.8 ~lcro~econd~. Tbe required delay to resy~chronlze i~ sent to tbo 40 1 328q 1 7 subscr~bex tor~lnnl ln ancrypted for~t over t~o ~M
data Btrea~ a8 ~ multlplexed flold ln tho ~udlo tag byte. T~e speclflc~tion s~nt ln the tag represents tho nu~ber of 1.8 ~icro~econd incre~ent8 to ~lay.
Th~ tl~e ~hlft ~peclflcatlon ls ~tatlc or any p~rticular televlsion programO but msy be changod ~ between progra~s. An audlo hlt ~noise) ~111 occur whon the change take~ placo. ~ new tlm~ shi~t specifleatlon 18 put lnto u~o ~hen the co~ntdo~n reaches zero. Co~patl~blllty ~lth ~tandard ~ync ~uppro~slon dQ~ra~blers ~ic~ are not usod ln connectlon ~ith the pre~ent lnvention can be provlded by uslng a ti~a ~hift of zero.
Certaln data i8 communlcated betwe~n th~ headend controller and the encod~r and subscrlber t~r~lnal using an PM data path. Some of tha ~M com~nds are trans~ltted on~-w~y ~e.g., from the he~dend to t~e ~ub~crlber torainal) whlle other~ are two-~ay commands. The one-way co~mands ar~ se~ SIG~ATU~, CLEAR ENTRY BUPF~R and LOAD OUEUE ENTRY X. Th~ two-way FM commands are SEND QUEUE ENTRY X, SEND
~K/NAK/STATU~, and SEND SIGNATU~E. The S M SIGNATURE
command i3 used during initl~lizatlon to do~nload a signature to a subscriber termlnal. The ~lgnature i8 ~ 1~ bit nu~ber, rando~ly a3signed to the subscriber terminal, and stored in the nonvolatlle ~emory of th~
terminal and ln the subscrlber re~ord ~in~alned by t~e headend eontroller. ~he s~gn~ture 1~ used aa a crypti~ key to send sen3itive data to the ~ubscriber .

:` :

~1 1328917 ~erminal ln a securo manner. The SET SIGNATUR~
command la a sp~cific comm~nd containing t~O byte8 o~
data.
Addltlonal FM co~mand~ aro used to control the subscriber diglt~l ~udlo termlnals. A S8T DIGITAL
AUDIO PARAMETERS command 1~ used to download audlo ~nd tag d~cryption key~. The audlo decryptlon key~ ~r~ a ~et of alght nlbbles, and th~ t~g docryptlon key~ ar~
a set of two nlbble~. One data byte 1~ trans~itted wlth the S~T DIGITAL AUDIO PARAM~TERS co~n~. Thls ~llow8 trans~l~sion ln ebe 11st for~at ~ltb ~inl~u~
impact to the system cyclq ti~o. ~ha byt~ i~ broken down into t~o fleld~; namely, a descrlptor f~ld ~for mo~t significant bit~ and a d~ta 1eld (for le~st significant bit~). The descrlptor field ldentiflo~
t~e spaclflc nlbble beiny downloaded, a~ do1nad ln Table 9.

42 1328~17 TA~LE_9 DESC~IPTOR DATA YI~LD CONTENT~
~ .
0000 Audlo dscryption key O
0001 Audlo decryptlon k*y 1 0010 ~udio dQcryption k~y 2 ooll Audlo decryptlon k~y 3 oloo Aud~o decrrptlon k~y 4 0101 ~udlo decryptlon koy 5 0110 ~udlo decryp~ion koy 6 lo 0111 Audlo d~cryptlon k~y 7 1000 T3g decryptlon k~y O
1001 Tag decryption key 1 1010 Not used 1011 Terminal Control 1100 Illeg~l 1101 Illogal 1110 Illegal 1111 ~llegal The terminal control nibble conta~n~ infor~ation pertaining to authorization of specif lt: features of the digital audio syste~. Four bit~ of control informatlon are downloaded, a~ illu~trated in Table lQ.

.~ ~

~3 t 32~q17 TABL~ l0 BIT DESCRIPTION

O SAP ~nablo/dl~abl~
0 ~ d1s~blo 1 ~ enablo l Stereo ~nabl~/dl~able 0 - di~able 1 - ~nabl-2 Not used 3 ~ot u~d Two version~ of ths SET DIGIT~L ~UDIO PARAMET~RS
command are available. The fir~t, a ~peclfl¢ ~ersion, contains an address ~nd i~ directed to an 1ndi~1dual subscriber terminal. The data byte trans~itted ~ith this speciflc command is encoded. The other version of the set digital audio parameter~ command i9 a global command dlrected to all subscriber terminals.
Data tran mitted in this version i~ sent in the clear t~.e., not encoded).

4~ ~32~ql7 The digltal audlo parameters ar~ ~ent ov~r the F~l d~ta path in an ~ncoded format, u~ing tho termin~l signature a~ a k~y. The ~lgnature 1~ ~ 14 blt nuJlber downloaded dur~ng t~rlolnal Inlti~llzatlo~ n~ 18 ~ent a~ two ~lght bit byte~. Bncryptlon and dQcryptlon of the ~igital audio p~ra~eters can be accompll~h~d u~ing - ^ variou~ codlng sy~t~ a~ ~111 bo appreci~ted by those skillcd ln tl~ art. An exalopla of ono such codlng l~ystea i~ that whlch result~ fro~ tll~ followlllg sQquence of operation~ which may be u~od to en~o~o ~h~
para~t~r byte prlor to tr~n~ S.on~
1) Swap bit~ 0 ~nd 1, and bit~ ~, and S, ~nd le~ve bits 6 and 7 and bits 2 and 3 ln tl~elr orlglnal po~ ltions .
Thi~ can be acco~plis~ed through th~
following ~equeneQ~ of op~ratlon~s (a) Lcglcally AND th~ byte Yit~ a mas~
pattern of 00100010, and ~hift th~ re~ultant byte right one po~ition. Store for further u~.
(b) Logically AND the original data byte with a mask pattern of 00010001, and shift the result left one position. Logically OR the result of this operaticn with the result of the operation in (a) above, and store for further use.
(c) Logically AND the original data byte with a mask pattern of 11001100, and logically OR the result of this operation with the re~ult of ~ nv~.
.

~5 1328~17 2) Excluslve NOR re~ult from l above wlth signature byto l-3) EXClU~iv0 OR re~ult fror~ 2 abov~ w~th ~ignatur~ byt- 2.
s ~) Cle~r MS~ of re8ult.
-Sn order ~o decrypt the parameter dat~ oncodcd u~ing the above sequence of operations, the following ~equenc~ i~ performeds 1) Exclu~lve O~ w~h ~ign~tur0 byte 2.
2) Exclus~vo NOR re~ult fro~ 1 abov~ ~lth signature byt~ 1.
3) Sw~p bit~ O and 1 and blt~ ~ and 5, and leave bits 2 and 3 and blts 6 and 7 ln the~r original po~itions~ Thi~ can be accomplis~ed u~ing the ~ame ~Igorlth~ described in ~tep 1 of ths encryp~ion ~sguence.
4) Cl~r ~SB of result.
The ~arious information and control infor~at~on provided from the headend controller to subscriber terminals can provide a variety of options in enabling or disabling receipt of the various vldeo and audio program siqnal~ transmitted over the cable televl~ion network. For exa~ple, t~e Upro~ram audio on SAP
channel~ flag sent in the control byte of th~ audlo tag exten~ion indicata~ whether the SAP or stereo right and left channel~ are to be con~idered the primary audio progra~ availabl~ to the subscriber. ~f the flag i8 ~et, for exa~ple, the SA~ chann~' c~n b~

6 1 328q 1 7 ~on~lderQd pr~mary audlo, and the lef~ and r~ght ~t~rso channe~ s~condary. If the flag 1B clear, then th~ stQreo left and rlght channel~ would be con~ldered pri~ry audlo and ~hb SAP channel secondary.
Two serv~ce code~ ~re trans~1tted ln the digltal audio tag, one for ~ideo a~d on~ for aud~oO Throuqh th~ U8e of the progra~ aud10 on ~AP c~ann~l flag ana the vldeo and audio service codes, a ~ub~cr~ber ter~ln~l c~n be ~u~orlzed to prov~de a vl~o progra-and Allow audio from ~ither the ~tereo or S~P
channol~, to dlsallow vldeo but ~llow audlo fro~
eith~r th~ SA~ or ster~o chann~l~, or to ~llo~ vidoo togeth~r wlth reception of bot~ tha ~AP and ~t~reo c~annels, ~t the subscrib~r'~ optlon.
R~ferrlng ~g~n to ~lgure 3, all aud~o and co~trol data encrypt~d by encryptor 58 1~ o~tput by the encryptor in sori~l for~ to a two blt s~ri~l to parall~l conv~rter 60. Timing logic 68 provldo~ a clock at 22 f~ to convert~r 60 ~hich outputs the d~ta in two bit parallel format to a multiph~se modulator 62. The multiphase modulation provided by ~odul~tor 62 is 8imilar to quadrature pha3e s~ft keyed (~QPS~) modulat~on but with th~ additlon of a fifth pha~
reference polnt. Timing logic 68 provide~ a clock at the horizontal line freguency fH to modulator 62.
Modul~or 62 i~ al~o provided with the ~05 MHz ~ound carrier frequency on which the audio d~tæ i~
~odul~ted .

~3~8917 Multi-phase modulator 62 is used to modulate the digital audio data. One audio frame of data is transmitted for each video line. The audio frame contains 22 symbols of two bits each, or 44 bits.
S The timing of the 22 symbols on each horizontal line is established by the 22 fH timing signal input to serial to parallel converter 60.
The first four bits in the audio frame are defined as the reference for demodulating the remaining bits. The ~eference is transmitted during the first two symbol periods of the line with an amplitude 6 dB greater than the amplitude of the remaining bits. The polar diagram 220 of Figure 7 depicts ~he phase of the transmitted reference signal as well as the bit values for each phase quadrant. As shown, the transmitted reference and recovered reference are 90 degrees apart. This is the phase lock loop (~PLL~) stable poin~ (i.e., the point where the PLL will lock).
As shown in Figure 7, the audio data is modulated such that each two bit symbol appears in a different quadrant, each 45 degrees from the axes of the polar diagram. The rightmost bit in each of the two bit symbols is shifted out of the transmitting shift register first, and into the receiving shift register first. There are ten possible data points used in polar diagram 220. Five of the data pvints occur on inner circle 221 (representing the n~rmal amplitude of ~a ~3289~7 the c~rrl~r slgnal), ~nd tha re~alnlng flve d~ta polnts are pre~ent on outer circle 223 (repr~entlnq AM ~odulated data ~t ~n ~mplitud~ of 6 d~ hlgher th~n ths nor~l carrier amplitude). ~wo of the t~n dat~
polnt~ corrsspond to the tranR~ltSod r~ferenc~ ~lgnal ~also referred to as a pllot sign~ nd the re~alning - elght data polnt~ correspond to the ~ultlphas~
~odulated audio d~t~. In th~ sub~crlbcr ter~lnAl ~hich rece~ves ~e ~odulatsd audlo data, ~ho A~
detector differ~ntl~t~s botween t~o presenco and absence of ~ d~ta blt by do.teG~lng ~b~thor t~c s~gn~l 1~ at th~ le~ol of the lnner clrcle 221 (a bln~ry zero) or at the level o outer clrclo 223 (~ binary one). The p~e of tha data doe~ not matt~r to ehe AM
detector.
Conver~ely, the phase det~ctor wblch recover~ the digltal audio signal doe~ not look at t~e a~plltude o~
the ~ign~l, b~t rat~er detect~ th~ p~ase t~eroof to determlne the ~ctu~l d~ta contained ln each of the t~o bit symbol~ li.e., either 00, 01, lû, or 11, depending on the quadr~nt in w~ich the data ~ppe~rQ~. The multiphase modulated digital audio data will commonly occur on inner circle 221 durlng each horlzontal line.
The only exception i~ immediately afeer the vertical inter~al, where ~he data will appear on outer c~rcle 223. The pilot slgnal (tran~itted reference) ~s comprised of AM modulated d~ta appear~ng on outer clrcle 223. The commonly occurring data po~nt~ ln ~igure 7 are repre~ented ~y solid circles and the q4 ~328917 infr~qu~nt data points (thoso occurrlng durlng th~
vertical lnter-~al) are ~hown by da~hed clrcle~.
On~e the digltal audlo data 18 ~ltlphase modulAtod, lt l~ then output from ~ultlpha~e ~odulator 62 to an AM ~odulator 6~ whero lt 18 rel~odulat~d on t~ .5 MHz sound carrler of the televls10n ~lgnal.
Data from headend controller SO whlch is not ~nco~ed by encryptor 58 is passed by l-icroproce~sor 52 d~r~ctly to AM mo~ula~or 64 for ~odulatlon on tho ~ound c~rrl~r. Thu~,~ tt~o dlgital audio inor~ation l~
carriod on th~ ~ound carrl~r u~lng aultlphaR~
modulation, ~hereas tlle vldeo vertical and horizont~l fra~lng, ~8 w~ t~le audlo carr1er ph~e refor~nc~
pilot signal, audio dat~ b~t tl~ and fram~ r~fsrenc~, progra~o identif ication3 ~nd dccryptlon seed~ ar~
carri~d on the ~ound carrler u~lng AM modul~tlon. A~
modulator 64 recelve~ the t~orlzont~ ann~ng frequency f~ froa tlming logîc 68 for U81~ In ~
con-~entional m~nner. The video ~nd horizontal framing information i~ input to AM ~odulator 64 from a standard sync separator 80 having been delayed by delay 84, which i8 used to synchroniz~ th~ video slgn~l wit)~ the audio carrier ph~se pilot ~lgnal.
Since different video transmitter3 will have diff~rent inherent delays, it is preerable th~e delay 84 be vari~ble delay a~ well known ln the ~rt In ord~r to ad~u~t the delay provided ther~by for proper synchronizat1on of the audio ~nd vld~o ~ign~ls. Th~
co~bined ~ulti-phase and .~.M ~odulated dlgit31 ~udlo 8~ 1 7 data replaces the FM modulated audio data which is normally provided on the 4.5 MHz sound carrier of a television signal.
A phase comparator 76, low pass filter 78, and voltage controlled oscillator 70 combine to provide a phase lock loop to maintain the proper horizontal frequency. Voltage controlled oscillator 70 runs at 18 MHz and the output thereof is divided by a factor of four at a first divider 72 to provide the 4.5 MHz frequency at which the sound carrier is centered and again divided by a factor of 286 at divider 74 to provide the horizontal frequency fH. The 18 MHz output of voltage controlled oscillator 70 is also input to timing logic 68 so that the various timing signals related to the horizontal frequency can be generated.
A standard 4.1 MHz low pass filter 82, video modulator and scrambler 86, and vestigial filter 88 are provided for modulating and scrambling the video signal in a conventional manner. A 45.75 MHz oscillator 90 provides the standard intermediate frequency ~IF) to the video modulation circuitry.
The IF frequency is mixed at mixer 92 with the modulated audio and control signals output from AM
modulator 64 after being filtered by a 4.5 MHz bandpass filter 66. This produces a sound carrier at the standard intermediate frequency of 41.25 MHz.
A 41.25 MHz ban~pass filter 94 filters the sound carrier which is subse~uently summed at a combiner 96 with the 1 32~9 1 7 modulated video signal from vestigial filter 88.
The composite IF signal is amplified by an amplifier 98 and input to a conventional channel upconverter 100 for conversion to an RF signal. The RF output of channel upconverter lO0 is input to a standard headend combiner 102 where it is combined with similar RF signals on inputs 103 from other television channels to be transmitted by the headend and with the FM data output from FM modulator 104.
The output of the hea~end combiner, on terminal 105, is the cable output signal which is sent via the cable system to individual subscriber terminals.
Those skilled in the art will appreciate that the RF
output signal on terminal 105 can also be transmitted by antenna or other means known in the art for reception by a subscriber terminal.
The multiphase modulator 62 of Figure 3 is shown in greater detail in Figure 4. The 4.5 M~z signal output from divider 72 (Figure 3) is phase shifted by 45 degrees by a conventional phase shifter 106 tFigure 43 and input to a mixer 112 to modulate the most significant bit of the two bit digital audio data input at terminal 111. The 4.5 MHz signal is also shifted an additional 90 degrees at conventional phase shifter 108 for modulating at balanced modulator 110 with the least significant bit digital audio data input at terminal 109.

, 1 32~9 1 7 The 4.5 MHz signal is also directly input to balanced modulator 114 where it is modulated with the phase and timing reference pilot signal input at termint terminal 113.
The output signals from each of modulators 110 (LSB data), 112 (MSB data), and 114 (phase and timing reference pilot) are all summed in a conventional summing circuit 116 to produce the sound carrier at terminal 118.
Figure 5 is a blQck diagram of a digital audio converter (contained in a subscriber terminal) used to receive a television signal modulated with digital sound in accordance with the present invention and to produce audio output signals from the television signal. The television signal, which is transmitted by conventional radio frequency (RF) techniques such as over a cable television system, is input at terminal 120. All FM control signals (e.g., subscriber terminal address signals, terminal signature, encryption keys and specifiers, control parameters, audio and video service codes, and program authorization data) are detected by FSK
receiver 154 and output to microprocessor 156 which processes the control signals in a conventional manner. Microprocessor 156 is also used to tune a dual conversion tuner 122 that tunes to specific television programs carried in the broadband RF
signal input at terminal 120. The construction and use of iual conversioh tuners in the television industry is well known~

1 32~9 1 7 Dual conver~lon tuner 122 ou~puts a co~po~lte I~
televl~ion slgnal for e~ch tele~lon cbannel ~hich 1-tuned. The composlt~ IF output~ correspond to those produced at t~e digltal audlo headend ~hown ln Y19uro s 3. S~e video portion of ~ co~poslte I~ signsl ln de3cra~bled at a convenelonal de~cram~lor 124 ~nd fllt~red by a conventlon~l Nygulst bandpa~s fl~ter 126 havlng a ~assband of 42-46 MHz. The filter~d signal fro~ bandpass filter 126 1~ d~odulated by ~ ~tandard demoJulator clrcul~ 130 whlch cont~ln~ ~ vid~o demodulator 132 and pha~e lock loop 13~ to produco ~
vidoo output fiign~l ~t termlnal 168 ln ~ conventlonal mann~r. Circuit 130 can co~pri~e, for ex~plo, ~n lntegrated eircult chip manufactured by ~itsubl3hl, lS Inc. and de~lgnated as model no. MS1365SP. A switch 166 controlled by ~icroprocessor 156 via tl~lng and decryptlon logic array 152 pr~vent~ a sub~crib~r fron receiving a v~d~o progra~ whlch i~ not aut~orized. In ~uch an in~tance, vldeo output tera~nal 168 1~
grounded by ~wltch 166 80 that no vld~o ~lgnal wlll be output to a su~acriber's televi~on set if unauthorized. A television modulator 164 modulates the video output signal pre~ent at termlnal 168 to provide an RF output ~ignal at terminal 170 ~n the event the ~ub~criber's t~levision does not h~ve an inpu~ to receive the video output signal directly fro~
terminal 168.

. :
:

132~ql7 The proce~slng of the audio portlon of th~
tQlevi~on slgnal wlll now be de~crlbe~. A televl~on IF cutput slgnal from dual COnVerB~On tUnGr 122 input to a ~1.25 MHz IP bandpa~ fllt~r 142. Th~
output of thls fllter i~ ~lxed in ~ntercarrlor ~lxer 136 with the output signal from phase lock loop 1~4.
Thl~ rQcovers the 4.5 M~z ~ound carrler, whl~h i~
filterQd by a 4.5 M~z bandpa~ flltor 14~. Th~ output from Çllter l~ lnput to an AM peak detector 146 which recc~var~ the pha~e and ti~lng refer~nc~ pllot slgnal that 1~ n~ces~ary ~:o de~odulat~ eh~ ~ulti-~ha~
modulatad dlgltal ~ound dat~. Tl~c pllot ~lgnAl detect~d by AM peak detector 146 1~ lnput to tl~lng and decryptlon logic array 152 whlch provlde~ ti~ g ~ignalQ to multi-phase demodulator 150.
Th~ ~ound carrier froro bandpa~s ~ilter, 1~.4 i~
al~o input to a d~gi~al lllaiter 138 con~ained lr~
demodulator circlJ~t 130 that li~it~ th~ alopll~ude of t~e lnput 8ignal, ther~by removing the AM modulated component~. The output of limit~r 138 is input tG a quadrature detector 140 contained ~n demodulator circuit 130 which detect~ the audlo ~lgnal and outputs it to multi-phaqe demodulator 150. Detector 140 will also detec~ a standard PM ~udlo ~ignal9 if input at RP
input ter~lnal 120 of th~ ~ub~ribar termlnal, ~o t~at ~he subscriber terminal will work with tslevi~ion 8ignal~ without digital ~ound. In ~u~h an ln~tanc~, switch 162 i~ 8witched to couple th~ FM audlo ~utput ~ignal to TV ~odulator 16~ where th~ conver.tional ~udlo 81gnal i8 modulated together wlth the vld~o sign~l for output to a televl~lon on tar~lnal 170. A
90 degree phas~ shift clrcu1t 148 ~ty~ically an L-C
tank circuit) 18 provlded Qxternally to demodulator circult 130 ~nd 1~ n~cessary for the operatlon of quadrature detector 140.
When th~ subs~rlb~r ter~nal of ~lgur~ S 1~ U~Qd to rec~lve a t~levl~lon signal contain~ng dlgltal audlo in Jccordanc~ with the presen~ inventlon, tho detected ~udlo sign~ tapped prlor to 90 ~egree phaso shlf~ ci~cuitry 14# for input to l-ultl-pha~o dems:~dulator 150. Mul~i-ph~e de~odulator 150 recov~r~
the dl~t~l data from ~ho modulated sound carr1~r.
She recovered data is input to ti~lng and decrypeion lS loglc arr~y lS2, which outpu~s ~t to ~daptlv~ d~lta ~odulatlon decod~r lS8 for r~cr~atlon of the origlnsl analog sound channel~. Thc l~f t and right stereo sound channol~ app~ar at t~r~inal~ 112 and 17~, rcsp~ct lvely. The SA~ sound channal appe~r~ ~t ter~inal 176. In order to accon~modate subscribar television sets that do not have separate audio channel inputs, the left and right ~tereo channel siqnal~ are summed by convention~l sum~ing clrcuit 160 and coupled to TV modulator 164 for input in RF form to th~ user'~ televi~ion set vla ter~inal 170. Those ~killed in tb~ art wlll appreeiatc that th~ SAP output ~19n~1 on termlnal 176 could ~imilarly be coupl~d v~
~odulator 16~ to ~ user's televi~lon 3~t.

1328ql7 Multi-p~as0 demodulator 150 19 ~hown ~n great~r detall in the block dlagr~ of Pigure 6. A ~.5 M~z ~ignal ls created by di~ldlng the output of an ~8 M~z voltage controlled o~clllator lhO by four at dlvid~r s 182. Th~ 4.5 MH~ ~lgnal 1~ lnput d~r~ctly to ~ flr~t ph~se co~p~rator ~sxclu~l~e 0~ gate) 186 and to ~
~ ~econd phase comparator 188 after belng ~hlftad 90 degre~J by ~ con~entlonal pha30 ~hift clrcuit 18~.
T~e other lnput~ o~ each of ph~se compar~or~ 186 ~nd 188 are coupled to t~o 4.5 M8z modulat~d ~ound c~rrl~r ~ich i~ to be d~odulated by the ~ulti-ph~se demodul~tor. Pha~e co~parator 186 ~ill de~odulate ~he most slgni f lcant bit o~ each symbol of tho d~gital audio data and phase comparator 188 ~ill demodula~e tt~e least slgnif icant bit of each sy~bol which i~ 90 degree~ out of phase ~lth the most signif îc~nt blt. A
low pas~ ~ilter 190 filt~r~ the output of phas~
comparator 186. Sl~llarly, D low pasa filter 192 fllter~ the output of pha~e comparator 188. The filtered outputs fro~ the low pas~ filters 190, 192 are sampled and held by sample and hold circuits 191 and 193, respectively. These signals are sampled in synchronization with the phase and timing reference pilot signal. The sampled ~ignals are output from the 3ample and )~old circuit3 to a voltags comparator 196 for resolv~ng the mo t significant bit and ~oltage comparator 198 for re~olving the lea~t ~i~nlf icant blt. Sample and hold c~rcuits 191 an~ 193 ar~ ~ell known, and can compri~e, for examp;e, a capacitor . - .
. .

57 13289t~

whlch 18 charged durlng the ~ampl~ng time to e~tabll~h a DC level, followed by an PET operatlonal ~mplifler.
Comparator 196 compares the output of low pas8 f llter 190 to th~ DC reference establl~hQd by sa~pl~ and hold clrcuit 191 and outputs tbe ~ost ~lgnlflcant blt on ter~lnal 208. Slm~larly, compar~tor 198 co~pares the output of lo~ pas~ fllter 192 to the DC lev~l establi~hed by s~r~ple and hold clrcult 193 and output3 the lea~t ~lgniflcant bit on ter~inal 210.
~n lnvertor 200 1~ couplod to the output of ph~e comparator 186, and 19 fed back vi~ s~lt~h 202 ~nd ~
low pa~ filter 206 to voltage controlled o~lllator 180. Switch 202 1~ closed ln re~pon~ to the phase and timing reference pllot signal thereby provldlng the pha~e lock control ~ignal to voltage controll~d osclllator 180.
The output of the ~lti-phase de~odulator 150 l~igure 5) 18 input to ti~ing and decryption logi~
array 152 which decrypts the data in accordan~o wlth the procedures set forth above and ~eparate~ the data into ~ix ~erial bit ~treams for input to adaptlve delta modulation decoder 158. The ~ix ~erial ~tream~
are the same as tho~e ~hown in Table 1 above. Four of the 44 bits recovered in each horizontal line by the multi-pha~e demodulator are unu~sd by adaptlve delta modulation decoder 158. These four bit~ are those relating to the pha~e lock and timlng functlona pre~loualy descrlbed.

5~ 1 32~9 1 7 Figure 8 deplct~ th~ wav~forms ln the time do~ain of the multi-ph~se modulated and det~cted slgn~
Wavefor~ 230 i3 the ~.5 MH~ multl-pha~ ~odulated lnput slgnal. Carrier 232 i8 ehe soun~ carr~r ~aving a center frGquency of 4.5 MHz. T~ arrier 1~ ~
mod~l~ted ~lt~ the phase and ti~lng referenco pllot ~ ~ignal ~ shown at 234, the peak A~ a~pl~tudo b~lng 6 dE above the ~tandard AM modulatlon s~own at 236. ThR
multi-phase ~odulation of sound c~rrler 232 i~
lndlcated at 237, and.contaln~ ~ho dlgltal audio data.
Wavefor~ 238 show~ th~ detectod p~ak A~
modulation wblch produces t~e ph~e an~ tl~lng re~erence pllot sign~l 2~0.
Waveform 242 illu~trates the detect~d most 3ignificant b~t data. A high bit level (e.g., a ln) ls shown at 244 and a low blt level ~e.g.,.~ ~0 shown ~t 246.
T~e detected lcas~ signiflcant bit dat~ is ~llustrated ln wav~or~ 248. A hlgh bit i8 ~hown at 252 and several low bit~ are shown at 254.
The space between poin~3 ~X~ and ~Y~ in axis 250 represents one horizontal line of the telev~sion signal. Twenty-two symbol periods ~4~ bits of multi-pha~e modulated data) are contained within each horizontal lin~.

sg 1 32~9 1 7 ~t should now be ~ppreclated that the pre~ent lnventlon provlde~ ~ televl~lon tran~ sion ~yste~
for provid~ng digltal sound and whleh can be u~ed ln con~unction vlth a cablo televlsion ne~work whereln ttle srldeo ~ignal in ~cra~blcd. Thre~ dlgltal aud~o chann~l~ are tlm~ dlvl~lon multlplexed on the audlo carrl~r, uslng co~bined ~ultl-pha~e and AM ~odulatlon.
The an~ udlo ~lgnal~ ar~ dlgltlzed ln tb~
preferred embodiment using ~daptlve dolt~ ~odulatlon.
Although ~ ~lnglo preferred e~bodllqent h~ on descrlbed hereln, t~o~e ~killod in tho art ~dlll recognlzs th~t variou adaptatlon~ and Rlodlf lcation~
may be mad~ thereto, without departing fro~ the 9pirlt and ~cope of the present lnventlon a~ de~ined ~n the followlng claim~.

Claims (46)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for providing a television signal with digital audio, said television signal comprising a standard video portion and an audio portion having a sound carrier within its standard bandwidth, said method comprising the steps of:
digitizing an audio signal;
modulating the digitized audio signal on the sound carrier portion of said television signal using multiphase modulation to obtain a bandwidth for said audio portion that is within said standard audio portion bandwidth; and combining said video portion and the modulated sound carrier to produce a composite output signal with said digitized audio portion not interfering with said standard video portion.

2. The method of claim 1 comprising the further step of amplitude modulating the sound carrier with a pilot signal for use as a phase reference in the multi-phase modulated signal.

3. The method of claim 2 wherein said pilot signal comprises a pulse added to the sound carrier once for each horizontal line contained in a television signal.

4. The method of claim 3 wherein said pilot signal is added to a portion of the sound carrier corresponding to the end of active video on each horizontal line.

5. The method of claim 3 wherein said pulse comprises a portion of the sound carrier which is modulated at approximately twice the amplitude of the remainder of the sound carrier.

6. The method of claim 1 wherein said composite output signal is provided at an intermediate frequency, and comprising the further step of:
converting said composite intermediate frequency output signal to an RF television channel signal for transmission.

7. The method of claim 1 wherein:
said video signal includes a luminance portion;
a whole number of data bits in the modulated sound carrier are transmitted per horizontal video scan; and said modulation is synchronized with a horizontal video scan rate such that a frequency spectra of the modulated sound carrier is registered with a frequency spectra of said luminance portion.

8. The method of claim 7 wherein said video signal also includes a standard chrominance portion having a frequency spectra interleaved with the frequency spectra of said luminance portion.

9. The method of claim 1 wherein said audio signal is digitized using adaptive delta modulation.

10. The method of claim 9 wherein said sound carrier has a center frequency that is phase locked to a horizontal scan rate of said television signal to maintain said center frequency at a value which is the product of the horizontal scan rate and an integer value.

11. The method of claim 10 wherein the adaptive delta modulation uses an audio sampling rate which is the product of said horizontal scan rate with an integer factor of said integer value.

12. The method of claim 11 wherein said horizontal scan rate is approximately 15.734 kilohertz, said sound carrier center frequency is approximately 4.50 megahertz and said video signal has a bandwidth of approximately 4.25 MHz.

13. The method of claim 12 wherein said adaptive delta modulation sampling rate is thirteen times the horizontal scan rate.

14. The method of claim 12 wherein said digitized audio signal comprises three time division multiplexed audio channels, and said digitizing step includes the steps of:
sampling the first and second of said audio channels at an adaptive delta modulation rate of thirteen times the horizontal scan rate; and sampling the third of said audio channels at an adaptive delta modulation rate of eleven times the horizontal scan rate.

15. The method of claim 14 comprising the further steps of:
alternately sampling frequency and amplitude companding data in each of said first, second and third audio channels at a sampling rate of one-half the horizontal scan rate.

16. The method of claim 2 wherein the multi-phase modulated digital audio data uses four symbol periods having phase angles from said phase reference of approximately 45 degrees, 135 degrees, 225 degrees, and 315 degrees, respectively.

17. The method of claim 16 wherein two bits of data are provided in each symbol period.

18. The method of claim 17 wherein each horizontal line in a television signal is provided with 22 two bit symbols of multi-phase modulated audio data corresponding to three separate audio channels.

19. The method of claim 1 comprising the further step of serially encrypting the digitized audio signal to deter unauthorized reception and reproduction of an audio program therefrom.

20. The method of claim 19 comprising the further step of:
amplitude modulating said sound carrier by video vertical and horizontal framing information, a pilot signal for use as a phase reference in the multi-phase modulated signal, television program identification data, and decryption seeds.

21. The method of claim 1 wherein the generated digitized audio signal is high fidelity.

22. Headend apparatus for providing a television channel signal with digital audio, said television channel signal comprising a standard video portion and an audio portion having a sound carrier within its standard bandwidth, comprising:
means for digitizing an audio signal;
means coupled to said digitizing means for modulating the digitized audio signal on the sound carrier portion of said television channel signal using multiphase modulation to obtain a bandwidth for said digitized audio portion that is within said standard audio portion bandwidth: and means for combining said video portion and the modulated sound carrier to produce a composite output signal with said digitized audio portion not interfering with said standard video portion.

23. The apparatus of claim 22 further comprising:
means for producing a pilot signal for use as a timing and phase reference for the multi-phase modulated signal; and means for amplitude modulating said pilot signal on said sound carrier.

24. The apparatus of claim 23 wherein said pilot signal is modulated on said sound carrier once for each horizontal line contained in a television signal.

25. The apparatus of claim 24 wherein said pilot signal is added to a portion of said sound carrier corresponding to the end of active video on each horizontal line.

26. The apparatus of claim 25 wherein said pilot signal is modulated on said sound carrier at an amplitude of approximately twice the amplitude of the remainder of the sound carrier.

27. The apparatus of claim 22 further comprising:
means for scrambling the video portion of said television signal by suppressing horizontal synchronization pulses in the video portion.

28. The apparatus of claim 22 wherein said audio signal is digitized using adaptive delta modulation.

29. The apparatus of claim 28 further comprising:
means for phase locking the center frequency of the sound carrier to a horizontal scan rate used in reproducing the video portion of said television signal, to maintain said center frequency at a value which is a product of the horizontal scan rate and an integer value.

30. The apparatus of claim 29 wherein said digitizing means uses an adaptive delta modulation sampling rate which is the product of said horizontal scan rate with an integer factor of said integer value.

31. The apparatus of claim 30 wherein said horizontal scan rate is approximately 15.734 kilohertz, and said sound carrier center frequency is approximately 4.50 megahertz.

32. The apparatus of claim 31 wherein said digitizing means uses an adaptive delta modulation sampling rate of 13 times the horizontal scan rate.

33. The apparatus of claim 31 wherein said digital audio signal comprises three time division multiplexed audio channels, and said audio signal generating means comprise:
means for sampling the first and second of said audio channels at an adaptive delta modulation rate of 13 times the horizontal scan rate; and means for sampling the third of said audio channels at an adaptive delta modulation rate of 11 times the horizontal scan rate.

34. The apparatus of claim 33 wherein said audio signal generating means further comprise:
means for alternately sampling frequency and amplitude companding data in each of said first, second and third audio channels at a sampling rate of one-half the horizontal scan rate.

35. The apparatus of claim 22 further comprising:
means coupled to receive said digital audio signal from said audio signal generating means for converting said signal to a two bit parallel output data stream for input to said modulating means.

36. The apparatus of claim 35 further comprising:
means coupled to said audio signal generating means for serially encrypting said digital audio signal to deter unauthorized reception and reproduction of an audio program therefrom.

37. The apparatus of claim 36 further comprising:
means for amplitude modulating said sound carrier by video vertical and horizontal framing information, television program identification data, and decryption seeds.

38. The apparatus of claim 22 wherein:
said video signal includes a luminance signal;
a whole number of modulated digital audio signal bits are transmitted per horizontal video scan; and said modulating means synchronize the modulation of said sound carrier with a horizontal scan rate of said video signal such that a frequency spectra of the modulated sound carrier is registered with a frequency spectra of said luminance signal.

39. A converter for providing reproduction of a television channel signal that is transmitted over a cable television system or the like, said television channel signal comprising a standard video portion with a standard video bandwidth and an audio portion within a standard audio bandwidth, said audio portion having a standard sound carrier carrying audio signals in digital format, said converter comprising:
a tuner for receiving said television channel signals, detector means coupled to an output of said tuner for detecting said audio portion of said television channel signal with said standard audio carrier modulated with said audio signals in a digital format, a multiphase demodulator coupled to receive the detected audio signal for demodulating the detected audio signal to produce digital audio data, decoding means for converting the demodulated digital audio data to an analog audio signal, and means for outputting said analog audio signal to a television set or the like.

40. The converter of claim 39 wherein said decoding means comprise an adaptive delta modulation decoder which provides left and right stereo audio output signals.

41. The converter of claim 40 further comprising:

means for summing the left and right stereo audio output signals from the adaptive delta modulation decoder;
means coupled to receive the summed left and right stereo audio output signals and a video signal for combining the audio and video signals;
and means for RF modulating the combined video and audio signals for input to said video appliance.

42. The converter of claim 39 wherein:
said detector means is capable of outputting a detected analog audio signal present on a television signal to which said tuner is tuned, and further comprising switch means coupled to receive either an analog audio signal from said detector means or an analog audio signal from said decoding means for selectively outputting one of said analog audio signals to said video appliance.

43. The converter of claim 39 further comprising:
FM receiver means coupled to receive transmitted data signals for recovering data necessary to decrypt the digital audio signals; and decryption means, coupled to receive the decryption data from the FM receiver means, for decrypting digital audio data recovered by said multi-phase demodulator means.

44. The converter of claim 39 further comprising:
AM peak detector means for recovering a pilot signal from the sound carrier portion of a television signal tuned by said tuner; and means for coupling the detected pilot signal to said multi-phase demodulator means for use as a demodulator phase and timing reference.

45. The converter of claim 39 wherein said demodulator means is synchronized with a horizontal video scan rate, and said decoding means is adapted to decode a whole number of digital audio signal bits per horizontal video scan.

46. The converter of claim 39 wherein said video signal has a bandwidth of approximately 4.25 MHz, and said detector means detect a digital audio signal modulated on an approximately 4.5 MHz sound carrier.