US3385937A - Hearing aids - Google Patents

Description

y 23, 58 JEAN-CLAUDE LAFON 3,385,937

HEARING AIDS Filed Jan. 29. 1964 l o 550 I000 1m 35011 4500 soon 7m and LID-J Fly 2.

.suMM/or/o/v nswcs EARP/IONE MICROPHONE PREAMP F (MIXER) 5 VARIAELE GAIN AMP a BPF 1 AMPLIFIER AND A MPLI TUDE DEMOD sl/MMA r/a/v EARPHONE MICROPHONE PRf/WP LPF DEV/Ct'fll/XEI?) MP 1 \2J 9 7 J0 11 .SUMMA r/o/v Dev/(5 (MIXER) AMPLIFIER AND AMPUTl/Df VARIABLE 64/ AMP BPF 6': INVE N TOR oscuurok E United States Patent 3,385,937 HEARING AIDS Jean-Claude Lafon, Saint-Rambert-lIle-Barbe, Rhone, France, assignor to Centre National de la Recherche Scientifique, Paris, France, a French Government administration Filed Jan. 29, 1964, Ser. No. 341,004

Claims priority, application France, Feb. 14, 1963,

7 Claims. (U. 179107) ABSTRACT OF THE DISCLOSURE An auditory prothesis device comprising a microphone, two band-pass filters connected to the output of said microphone for passing, respectively, frequencies ranging, on the one hand, from 1500 to 3500 c.p.s. and, on the other hand, from a lower limit ranging from 4500 to 6000 c.p.s. to an upper limit ranging from 7000 to 8000 c.p.s., means for detecting the amplitude of the signals passed through each of said filter means, two oscillators for producing each a distinct alternating voltage of a frequency ranging from 350 to 1000 c.p.s., a modulator for modulating the voltage supplied by each of said oscillators in accordance with the output of each of said detecting means, respectively, means for mixing the modulated voltages supplied by said two modulators, an amplifier connected to the output of said microphone in shunt with said band-pass filters, a mixer having two inputs connected respectively with the output of said amplifier and with the output of said mixing means and an earphone having its input connected with the output of said mixer.

The present invention relates to hearing aids or auditory prosthesis devices.

The chief object of the present invention is to provide a device of this kind which is better adapted to meet the requirements of practice, in particular which permits of making the sounds of a speech more intelligible to a deaf person.

According to the essential feature of the present invention, such a device comprises, in combination, a microphone for transforming acoustic signals into electric signals, two band-pass filter means for passing only the electric signals delivered by said microphone the frequencies of which range substantially on the one hand from 1500 to 3500 cycle per second and on the other hand from a lower limit ranging from 4500 to 6000 cycles per second to an upper limit ranging from 7000 to 8000 cycles per second, respectively, amplitude detecting means for detecting the envelope of the signals passed through said filter means, compensating means for producing an alternating voltage of a frequency ranging from 350 to 1000 cycles per second, means for modulating the voltage supplied by said compensating means in accordance with the output of said detecting means, means for amplifying the modulated voltage supplied by said modulating means, and an earphone for transforming the voltage thus amplified into acoustic signals.

According to another feature of my invention the hearing aid device further comprises, between the microphone and the earphone, filter means for passing only the electric signals from the microphone having a frequency below 1000 cycles per second and means having their out ut connected with the last mentioned filter means for transmitting the signals therefrom to the earphone.

A third feature according to my invention consists in providing two separate chains respectively for the signals ranging from 1500 to 3500 cycles per second and for 3,385,937 Patented May 28, 1968 these ranging from 4500 (or 6000) cycles per second to 7000 (or 8000) cycles per second, each of these chains comprising a filter, an amplitude detector and a modulator for mixing the detected signals with a compensating reciprocating voltage of a frequency chosen within the range from 350 to 1000 cycles per second, the compensating frequencies being different for said two chains respectively.

Preferred embodiments of my invention will be hereinafter described with reference to the appended drawing, given merely by way of example, and in which:

FIG. 1 is a diagram illustrating the principle of my invention;

FIG. 2 is a diagrammatical view of a hearing aid device made according to a first embodiment of the invention;

FIG. 3 is a view similar to FIG. 2 relating to another embodiment of the invention.

It should first be reminded that seriously deaf persons perceive only sounds of a relatively low frequency, ranging for instance from 20 to 1000 cycles per second.

In order to improve the hearing of such persons and in particular to give them information relative to the remainder of the frequency band corresponding to speech (that is to say from 1000 to 7000-8000 cycles per se ond), it has already been proposed to filter high-pitched sounds and to modulate with the filtered signals thus obtained a low-pitched sound of a frequency ranging within the band that can be heard by the deaf person.

But, up to the present time, on the one hand the ire quency band chosen for the low-pitched sound was lower than 300 cycles per second so as to correspond to the frequency band best audible for deaf persons and possibly to provide several harmonics and on the other hand, the filtered sounds were distributed over the whole partial band in question.

Now the first of these features practically prevents the deaf person from distinguishing the loud sounding consonants from muffled consonants and the second of said features has for its effect to produce multiple signals a great number of which is unnecessary and prevents a good understanding of the message that has been formed, while complicating the apparatus.

I have found by studying the components of human speech: that on the one hand the utilization of a compensating low-pitched sound of a frequency lower than 350 cycles per second masked the low-pitched components (of frequencies ranging from 20 to cycles per second) of loud sounding consonants b, as in boat, d, as in day, g, as in go, and chiefly as in zeal and v, as in vote and j as in jazz, so that these components can no longer be distinguished from the corresponding mufiied consonants, such as p as in pay, t as in two, k as in case and chiefly s as in sun, 1 as in foot and sh as in show, respectively; and that, on the other hand, the only phonemes of frequencies higher than 3500 cycles per second that are useful in practice are the muffled spirants s, as in sun and f, as in foot, and the loud spirants z, as in zeal and v, as in vote an important amplitude of which corresponds to the frequencies ranging from 6000 to 8000 cycles per second and possibly phoneme y, as in you, the portion of which sutficient for a good intelligibility corresponds to frequencies ranging from 4500 to 5500 cycles per second.

Furthermore it was found that the range of frequencies between 1000 and 1500 cycles per second essentially com prised, as sound elements necessary for understanding speech, those relating to vowels identifiable by mere lip reading.

Starting from these facts and also from the fact that a person suffering from serious deafness perceives sounds of frequencies lower than 1000 cycles per second, I transpose, according to the present invention, the information portions of speech having frequencies ranging on the one hand from 1500 to 3500 cycles per second and on the other hand from 45006000 to 7000-8000 cycles per second by replacing them by at least one low-pitched sound of constant frequency ranging from 350 to 1000 cycles per second modulated by the curve forming the envelope of the amplitudes of said portions of speech.

This transposed low-pitched sound preferably is a pure sinusoidal sound but it might also be of any other desired nature, for instance an aleatory noise, either filtered or not.

Its frequency may be chosen as low as 400 cycles per second in apparatus to be used for deaf persons which do not perceive any sound having a frequency exceeding 500 cycles per second. However preferably its frequency is chosen in the range from 800 to 1000 cycles per second.

I thus obtain, with a relatively simple apparatus, an intelligible reproduction of human speech, owing to the fact that the artificial signals on the one hand do not mask the low-pitched components of loud sounding consonants and on the other hand comprise but a minimum number of parasitic sounds.

The principle of the invention is diagrammatically illustrated by FIG. 1, where the frequencies are plotted in abscissas and the amplitudes in ordinates.

The curves A and B are the curves of response of the band-pass filters corresponding respectively to the frequency bands of from 1500 to 3500 cycles per second and from 6000 to 7500 cycles per second. The dot-anddash lines indicate the transposition of the filtered sounds from these frequency hands into a compensation sound C the constant frequency of which is within frequency band D ranging from 350 to 1000 cycles per second. FIG. 1 further shows at M the response curve of another bandpass filter corresponding to the frequency band ranging from 4500 to 7500 cycles per second, this filter being used instead of that corresponding to the frequency band from 6000 to 7500 cycles per second if it is desired to take phoneme y into account as above stated.

FIG. 2 shows a first embodiment of the invention.

This embodiment comprises:

A microphone 1 transforming the acoustic signals it receives, produced by human speech, into electric signals,

A preamplifier 2 fed with these electric signals,

Two band-pass filters 3 and 3 adapted to pass among the preamplified signals, only those corresponding respectively to frequencies ranging from 1500 to 3500 cycles per second for 3 and from 4500 (or 6000) to 7000 (or 8000) cycles per second, for 3 System 4 for amplifying and detecting or demodulating the signals filtered by 3 and 3 which may include a conventional amplitude or envelope detector that develops a varying D C. signal which follows the envelope of the input signal components,

A source 5 capable of producing a sinusoidal voltage of constant frequency ranging from 350 to 1000 cycles per second (preferably from 800 to 1000 cycles per second) if the deaf person for which the apparatus is intended is capable of perceiving sounds corresponding to this 800l000 band,

An adjustable gain amplifier 6 energized both by the output of detecting system 4 and by the sinusodial voltage from source 5, so as to have said voltage modulated by the curve forming the envelope of the two portions filtered at 3 and 3 of the speech received at 1,

An amplifier 7 for the voltage thus modulated, and

An earphone 8 capable of transforming the electric signals at the output of amplifier 7 into acoustic signals fed to the ear or cars of the deaf person.

The low frequency portion of the speech, which can be heard by said person may be directly received by him after amplification.

However it is preferred to filter and to amplify this 4. last mentioned portion in the same apparatus as the other speech portion so as to send to the car of the deaf person only the sounds that may be useful.

For this purpose, I connect with the output of preamplifier 2 a low-pass filter 9, for instance the cutoff frequency of which is 1000 cycles per second and the output of this filter 9 is mixed (summed) with that of the adjustable gain amplifier 6 in a mixer (summation device) 10 the output of which is connected to the input of amplifier 7. It will be understood that the term mix or mixer as used throughout should be taken in the sense of addition or summation of signals and not in the sense of nonlinear modulation with production of side bands and the like.

FIG. 3 shows another embodiment of the invention.

In this embodiment every element the function of which is analogous to that of the corresponding element of the system of FIG. 2 is designated by the same reference character.

This second embodiment differs from the first one merely in that it uses two compensation signals instead of a single one.

Source 5 is therefore replaced by two distinct sources 5 and 5 each producing a sinusoidal voltage the constant frequency of which ranges between 350 and 1000 cycles per scond, the frequencies of said sources 5 and 5 being different from each other.

The amplifying and envelope detecting system 4 of the first embodiment is in this second embodiment replaced by two systems 4 and 4 respectively, each of which treats one of the signals issuing from filter 3 and filter 3 respectively. The outputs of said systems 4 and 4 are applied to two adjustable gain amplifiers 6 and 6 further energized by voltages supplied by 5 and 5 respectively.

The modulated signals obtained at the outputs of amplifiers 6 and 6 are mixed (added) together at 11 before being further mixed (added) with the signals coming from filter 9.

Of course use can be made of miniaturized circuits including semiconductors.

With the arrangement according to the present invention, I apply to the ear of a deaf person an information comprising, in addition to the low frequency sounds of speech that can be directly heard by him, a low frequency image of the high-pitched portion of this speech, this image being free from unnecessary parasitic sounds and being adapted not to mask the low frequency components of the loud sounding consonants.

In a general manner, while I have in the above description disclosed what I deem to be practical and efficient embodiments of my invention, it should be well understood that I do not wish to be limited thereto as there might be changes made in the arrangement, disposition and form of the parts without departing from the principle of my invention as comprehended within the scope of the appended claims.

What I claim is:

1, A hearing aid device which comprises, in combination, a microphone for transforming acoustic signals into electric signals, two band-pass filter means having their respective inputs connected with the output of said microphone for passing the electric signals delivered by said microphone within two frequency bands, respectively, one of said frequency bands ranging substantially from 1500 to 3500 cycles per second and the other of said frequency bands having its lower limit within the range of 4500 to 6000 cycles per second and its upper limit within the range of 7000 to 8000 cycles per second, means having the input thereof connected with the output of said filter means for detecting the amplitude of the signals passed through said filter means, compensating means for producing an alternating voltage of a fixed frequency of a value ranging from 350 to 1000 cycles per second, means having the input thereof connected both to the output of said compensating means and to the output of said detecting means for amplitude modulating the voltage supplied by said compensating means in accordance with the output of said detecting means, means connected to the output of said modulating means for amplifying the modulated voltage supplied by said modulating means, and an earphone connected to the output of said amplifying means for transforming the amplified voltage supplied by said modulating means into acoustic signals.

2. A hearing aid device which comprises, in combination, a microphone for transforming acoustic signals into electric signals, two band-pass filter means having their respective inputs connected with the output of said microphone for passing the electric signals delivered by said microphone within two frequency bands, respectively, one of said frequency bands ranging substantially from 1500 to 3500 cycles per second and the other of said frequency bands having its lower limit within the ran e of 4500 to 6000 cycles per second and its upper limit within the range of 7000 to 8000 cycles per second, two amplitude detecting means having each the input thereof connected with the output of one of said filter means, respectively, for detecting the amplitude of the signals passed therethrough, two compensating means, each for producing an alternating voltage of a frequency of a value ranging from 350 to 1000 cycles per second, the frequencies of the voltages delivered by said respective compensating means being different from each other, two means having each two inputs connected to the output of one of said compensating means and to the output of one of said detecting means respectively, for modulating the voltages supplied by said compensating means in accordance with the output of said detecting means, mixing means having two inputs connected with the respective outputs of said modulating means and an output means connected to the output of said mixing means for amplifying the voltages supplied by said mixing means, and an earphone connected to the output of said amplifying means for transforming the two amplified voltages into acoustic signals.

3. A hearing aid device according to claim 1 further including low-pass filter means coupled between said microphone and said earphone for passing from said rnicrophone to said earphone only signals of a frequency below approximately 1000 cycles per second.

4. A hearing aid device according to claim 3 further comprising a mixer having its output connected with said earphone, said mixer having two inputs, one connected with the output of said low-pass filter means and the other connected with the output of said modulating means.

5. A hearing aid device according to claim 4 further including, by-pass filter means inserted between said microphone and said earphone for passing from said microphone to said earphone only signals of a frequency below approximately 1000 cycles per second.

6. A hearing aid device according to claim 5 further comprising a mixer having its output connected with said earphone, said mixer having two inputs, one connected with the output of said low-pass filter means and the other connected with the output of said mixing means.

'7. A hearing aid device comprising transducer means for producing electrical signals corresponding to received information bearing audio signals, reproducing means receiving the transducer signals for separating electric signals in the range of 1500 to 3500 and 4500 to 8000 cycles per second and developing two signals each with a characterisic which varies according to the information content of opposite ones of said ranges of signals and varying each of at least one fixed frequency carrier signal in accordance with said characteristics variations of said two signals respectively and another transducing means producing audible signals at the frequency of the at least. one carrier frequency and said audible signals varying according to the information of the electric signals in said ranges.

References Cited Campanella, 8.1.: A Survey of Speech Bandwidth Compression Techniques, IRE Transactions on Audio, p. 104- 116, Sept-Oct. 1958.

KATHLEEN H. CLAFFY, Primary Examiner.

WiLLIAM C. COOPER, Examiner.

A. A. MCGILL, Assistant Examiner.

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