WO2001082513A1

WO2001082513A1 - Method and device for coding data on the audio tape of a sound transmission system

Info

Publication number: WO2001082513A1
Application number: PCT/FR2001/001223
Authority: WO
Inventors: Philippe Bertrand
Original assignee: Communications Sa
Priority date: 2000-04-21
Filing date: 2001-04-20
Publication date: 2001-11-01
Also published as: AU2001254893A1; FR2808141A1

Abstract

The invention concerns a data encoding device characterised in that it comprises: a first system (1) located at the production of the sound signal and including binary coding means (3) for producing a bit stream comprising a control code for an apparatus operating the audio tape, means for modulating the produced code (3), an interface (4) for injecting the produced code into the next device of the sound processing chain, and a second system (2) located inside or proximate to the apparatus broadcasting or receiving the sound signal and comprising a code identification system (9), which decodes the signal and an interface for transmitting (9) the code to the apparatus so that it operates on the received data.

Description

"METHOD AND DEVICE FOR CODING INFORMATION ON THE AUDIO BAND OF A SOUND TRANSMISSION SYSTEM"

The invention relates to a method and a device for coding information for an apparatus exploiting the audio tape of a sound transmission system or simply of an audio document.

To use the functions of a device, it is a matter of transmitting an appropriate control code to it using the channel through which the sound is sent to it.

Such methods and devices can be used for example:

- To control a video recorder, to record a television program.

- To control the decoder, descrambling of television programs.

- To encode information on audio documents such as audio CDs, DVDs, Internet MPEG MP3 files for marking purposes.

- For audience measurement.

- For anti-violence systems: coding of the parts (or of the whole) of films or programs so that the broadcasting device masks or encrypts them.

Several systems have been proposed to solve this problem.

In order to control the start and stop of a remote video recorder, a system consists in using the sound signal to convey information about the start and end of the broadcast as well as the pause.

There are now digital coding systems for the soundtrack and even the entire television program. These systems use a defined frame of digital signals usable for transport not only sound but also image and data. Thus, certain television channels transmit part of their program, in particular films, with stereophonic sound. This transmission of stereophonic sound takes place using a system known as NICAM. The NICAM system allows the transmission of signals corresponding to digital codes on the two stereophonic sound channels and to restore them in digital form after reception.

According to an earlier patent application of the applicant, a system of this type is used to remotely program a video recorder, that is to say, at least for sound, digital coding, to transmit commands to the recording device. operation at a specific time.

To this end, according to this request, a binary code is developed, including in particular the data representative of the start, suspension, resumption or end of the emission to be recorded, the signal corresponding to the code is modulated, transmits the modulated code to at least one sound channel (right and / or left) instead of sound and the assembly to the sound input of the coding system of the digital or analog transmission system used, which performs the processing of signal and transmits it to the transmitter. When the emission is received, the signal conveying the code and the signal conveying the sound are separated and the emission code is demodulated and the data are transmitted to the programming system of the recording apparatus for the execution of the transmitted commands.

The drawback of this system is that when the signal containing the code is transmitted, the listener hears the transmitted code as a noise from the sound channel. In addition, it requires the use of a specific sound transmission system (NICAM). The invention aims to overcome these drawbacks by creating a system for transmitting information to a device, in particular a recording device, the signals of which cannot be detected by ear when they are used.

To do this, the code is no longer transmitted, by the sound channel, in place of the sound but superimposed on the sound, in a proportion such that the distortion of the latter is not audible.

To this end, the process is characterized by the following steps:

- development of a binary code including in particular the data representative of the message to be coded,

- modulation by the binary code of a key signal of characteristic shape to obtain a coded signal in which each bit 1 or 0 is represented by the period of the key signal or the inverted key signal respectively, - addition of the coded signal to the sound,

- transmission of the assembly to the sound input of the digital or analog transmission or recording system used, which performs conventional signal processing,

- reading of the sound and detection of the vehicle signal code ₇ - demodulation of the restored code,

- use of the data thus obtained ^r to the device using the audio tape,

- use of transmitted data.

According to a particular characteristic of the invention, before adding the coded signal to the sound, the form of the sound signal is checked so as not to add the coded signal to it if it has a shape close to that of the sound signal at the same time. . The invention also relates to a device for implementing the method.

The device comprises a first system located at the source and comprising:

a binary coding means intended to develop a bit stream comprising a code which corresponds to a message intended for a sound processing apparatus,

- a key signal generator of predetermined shape and frequency, - a means of modulating the code developed with the direct or reverse key signal,

an amplification means for determining the proportion of the signal containing the code relative to the transmitted sound signal,

a summing means making it possible to add the code signal to the sound signal in the proportion determined to transmit it,

and a second system located in the apparatus which has to interpret the code and comprising:

a system for recognizing the presence of the key signal, comprising a filter reacting to the correlation of the received signal with the key signal and which generates a peak corresponding to a bit of the message,

- A means of interpretation of the code received.

According to a particular characteristic of the invention, the device comprises, interposed between the modulation means and the amplification means, an inhibition means receiving on the one hand the sound signal and on the other hand the code to compare their shape and inhibit the transmission of the code if the form thereof is not sufficiently distinct from that of the sound. The invention will be better understood by means of an exemplary embodiment represented in the appended drawing, in which:

FIG. 1 schematically shows a first embodiment of the system for transmitting the sound signal and the code according to the invention;

Figure 2a shows by way of example the form of a key signal;

FIG. 2b shows the principle of coding the message,

Figure 3 shows the structure of the signal containing the message

FIG. 4 schematically shows the reception and decoding system according to the invention

FIG. 5 schematically shows a second embodiment of the system for transmitting the sound signal and the code according to the invention.

As shown in FIGS. 2a and 2b, a key signal represented diagrammatically (the key signal is a digital signal, it is therefore a series of discrete points), of predetermined shape over a period to be recognized, is produced and transmitted, under its direct form to represent a bit at 1 and in its inverted form to represent a bit at 0, according to a binary code itself developed to transmit a message to a sound processing device. The spectral response of the key signal fully occupies the frequency band between Fa and Fh located in the audible range.

The structure of the message shown in FIG. 3 includes a preamble whose number of bits, 0 or 1, is sufficient to allow the decoder to detect the key signal embedded in the sound signal and to prepare for receiving the message. The preamble is also used to remove the indeterminacy of the sign.

This preamble is followed by a start bit, opposite to the bits in the preamble, which indicates to the decoder that the following bits are the bits of the message.

The last part of the structure is made up of the message itself.

As shown in FIG. 1, a binary code 1 intended for a sound or other device for broadcasting a sound program or a sound medium is transmitted to a modulator 3 to modulate the key signal 2. The signal thus obtained is then amplified by an amplifier 11 and sent to a proportion calculator 4 which determines the proportion of modulated key signal to be added to the sound signal to make it detectable without disturbing the latter. For this, the system estimates the strength of the sound signal in the frequency band of the code (from Fa to Fh); the higher this power, the less noticeable the key signal, so it will have to be stronger.

The modulated and proportional key signal is then added at 5 to the sound signal. The digital sound signal is processed in blocks of samples corresponding exactly to a period of the key signal (for example 512 samples for the coder and 256 for the decoder). The whole is transmitted either to a transmitter, radio or television, or to a sound medium to convey the message intended for a sound processing device.

The decoding for the use of the device concerned is carried out according to the figure

4, thanks to a filter 6 which produces a convolution product between the sound signal and the key signal over a period of the latter. An analog / digital converter 10 is mounted, in parallel on the audio circuit, in upstream of the filter 6 to convert the received signal into a digital signal if the latter was analog.

This product has the form:

f (t) * g (t) = [f (t-τ) -g (τ) -dτ

With f (t) the sound signal, and g (t) the key signal, and where T is the period of the key signal, t time and τ the domain.

The result is a correlation peak which is detected by a contrast threshold detector 7 which transmits a bit for each peak to a code interpreter not shown. The decoder hooks onto the correlation peaks and estimates the phase shift in order to best adjust the filter to synchronize with the signal. Thus the probability of signal detection is maximized.

FIG. 5 shows a second embodiment of the invention which makes it possible to avoid sending the message when the decoder risks not to detect it because of a shape of the sound signal too close to that of the signal. key.

For this, a decoder identical to that shown in Figure 4 is mounted between the arrival of the audio signal and the input of the key signal modulated with the message. The audio signal is compared in an inhibition circuit 8, which, when the form of this signal is too close to that of .du. key signal so that the decoder can detect its presence, inhibits the transmission of the key signal modulated by the code until the difference between the two signals is perceptible for the decoder.

In the embodiments shown in FIGS. 1 and 5, the level of the sound signal is slightly attenuated at the time of coding in an attenuator 9 so that the superposition of the key signal does not saturate the device. When the key signal is not present, the attenuator 9 lets through 100% of the sound signal.

The operation of the system will now be described with reference to FIGS. 5 and 4:

When a message has to be coded on the audio signal of a soundtrack, system 1 produces a repeated key signal of the same sign in order to warn the destination device of the presence of a message. This succession of key signals is compared at 8 to the sound signal. If the form of the sound signal analyzed by the integrated decoder 6, 7 is too close to that of the key signal at this instant, the inhibition device 8 delays the transmission of the message, until the key signal is sufficiently distinct from the sound signal. Then, after passing through a variable gain amplifier 11, the key signal train is added to the sound. A proportion calculator 4, placed in parallel on the output of the system, makes it possible to increment the gain of! amplifier 11 if the amplitude of the key signal train is estimated to be too low.

On reception, the destination device performs the convolution product in the filter 6 to produce the peaks indicative of the presence of the key signal that the detector 7 will detect. The latter will allow the decoder to synchronize.

Upon the occurrence of a key signal inverted, the decoder 6, 7 will transmit all the bits corresponding to each direct key signal or inverted as qύe ^~ message to the camera and it will then execute the transmitted command.

When the sound signal is analog, the analog / digital converter 10 mounted between the input of the combined signal and the decoder will convert the signal to make it intelligible to the decoder.

Claims

1. - Coding and decoding method intended to pass information into the audio tape of the system exploiting it

characterized by the following stages:

- development of a binary code including in particular the data representative of the message to be transmitted,

modulation by the binary code of a key signal of characteristic shape to obtain a binary coded signal in which each bit 1 or 0 is represented by the period of the key signal or of the inverted key signal respectively,

- adding the coded signal to the sound,

- transmission of the assembly to the input of the next device, digital or analog, which performs the conventional sound processing,

- the broadcasting, filtering and analysis of the signal carrying the code and the sound,

- demodulation of the restored code,

- transmission of the data thus obtained to the device using the audio tape,

- use of transmitted data.

2. - Method according to claim 1 characterized in that, before the insertion of the coded signal to the sound, the shape of the sound signal is checked so as not to transmit the code signal if it has a shape close to that of the sound signal at the same time.

3 Method according to claim 1 characterized in that the amplitude of the key signal train is incremented if it is estimated to be too low.

4. - Programmable control device for implementing the method according to any one of the preceding claims, characterized in that it comprises a first system located at the source and comprising:

- a binary coding means (1) intended to develop a bit stream comprising a code which corresponds to a message intended for a sound processing apparatus,

- a key signal generator (2) of predetermined shape and frequency,

- a means of modulating the code developed with the key signal (3) which produces a direct or reverse key signal,

- amplification means (11, 4) for determining the proportion of the signal containing the code relative to the transmitted sound signal, - summing means (5) making it possible to add the code signal to the sound signal in the proportion determined for the transmit, and a second system located at the entrance of the device to receive the code and comprising:

- a system for recognizing the presence of the key signal, comprising a filter (6) reacting to the correlation of the signal with the key signal which generates a peak corresponding to a bit of the message,

- a means of interpretation of the code received (7).

5 - Device according to claim 4, characterized in that between the modulation means (3) and the amplification means (4) is interposed an inhibition means receiving on the one hand the sound signal and on the other hand the code to compare their form and inhibit the transmission of the code if its form is not sufficiently distinct from that of sound.