GB2224413A

GB2224413A - Electronic hearing aid

Info

Publication number: GB2224413A
Application number: GB8825337A
Authority: GB
Inventors: Andrew David Patrick Godfrey; Michael Adrian Lynch
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-10-28
Filing date: 1988-10-28
Publication date: 1990-05-02
Anticipated expiration: 2008-10-28
Also published as: GB2224413B; GB8825337D0

Abstract

The hearing aid enhances human hearing, counteracting defects or aiding normal human hearing in difficult environments. Sound waves are converted into an electrical information signal in Stage 1. The amplitude of the information signal is monitored in Stage 3 and Stage 6, and adjusted in Stage 2 as required. The amplitude of an electronically generated signal, Stage 4, at a frequency above the highest audible frequencies is adjusted in Stage 5. These two signals are then mixed in Stage 7 and subjected to compression in Stage 8. The amount of compression experienced by the information signal is dependant on the amplitude of the electronically generated signal. Filtering of the information signal takes place in Stage 9 and the resultant information signal is supplied to transducers in Stage 10 which convert it back into sound waves. <IMAGE>

Description

ELECTRONIC HEARING AID This invention relates to an electronic hearing aid.

Electronic hearing aids are devices used to enhance human hearing.They convert sound waves into electrical signals,which are then electronically manipulated.This is done in order to counteract problems caused by defective human hearing or to aid normal human hearing in difficult environments. The manipulated signals are then converted back into sound waves.

There are three major defects in human hearing, mainly due to the aging process,which can be addressed by hearing aids producing an audio output.

The first two defects,reduced gain and reduced frequency response,are relatively simple to counteract.However,the third defect being the inability to,when required,ignore background sounds,particularly those which are low in frequency,has not previously been satisfactorily overcome.The third defect is most noticable in environments where there are many sources of sound,such as busy streets or social gatherings.

People suffering from these defects can have great difficulty in distinguishing between important sounds and background sounds.

Conversations in pubs,clubs,day centres etc. become difficult to understand, requiring continual concentration, and disorientation in noisy streets lay be experienced.The present invention,therefore, as well as addressing the first two defects incorporates a process especially to counteract the third defect, enabling the user to hear more effectively in even the most difficult situations.

The two most difficult environments for normal human hearing are as follows:factories etc. ,where there are constant very loud background sounds; and situations where extremely low amplitude sounds need to be monitored but where unexpected high amplitude sounds may also occur.

The present invention can be used to provide automatic protection for these environments while allowing for the need for conversation etc.

The present invention incorporates ten stages of circuitry.The connection of these stages is illustrated by Fig.l,where connections a) and b) are alternative paths depending on the application.The circuitry and the component values of each stage may be altered to suit the application but stage function and overall system remains the same.

Referring to Fig.l,sound waves enter Stage 1, where they are converted into electrical signals by a microphone transducer and an amplification circuit.This amplified electrical signal,hereafter known as the Information Signal, is monitored by Stage 3.The circuitry of Stage 3 can either be of a threshold type ,producing a switching control signal when a static threshold is exceeded,or of a proportional type whereby the produced control signal bares some mathematical relation to the amplitude of the Information Signal i.e. inversely proportional, proportional etc.The signal derived from Stage 3 is used to control the gain of the Stage 2 voltage controlled amplifier (V.C.A.) circuitry.Thus as The Information Signal passes through Stage 2 its amplitude can be altered as required by the application.

Stages 4,5 and 6 have a similar structure in that the signal derived from Stage 4 passes through Stage 5, where its amplitude is altered according to a control signal derived from Stage 6. In this case ,however,Stage 4 is an electronic signal generator,which produces an electronically generated signal,hereafter known as E.G.S., containing only frequencies above the stated range of frequencies of the Information Signal.This signal is important to the function of the invention,being used to control the manipulation of the Information Signal in later stages of circuitry.The amplitude of the E.G.S. is varied as it passes through the V.C.A. circuitry of Stage 5.This variation is controlled by a signal derived from Stage 6.Stage 6 circuitry is similar to that of Stage 3,in that it can be either of a threshold type,or a proportional type.However,Stage 6 can monitor a dynamic threshold, a static threshold or a combination of the two depending on the application.The signal which Stage 6 monitors is derived from either Stage 1 or Stage 2,as indicated by paths a) and b) of Fig.l.

Stage 7 has mixing circuitry which combines the Information Signal and E.G.S. in the correct proportions * and which gives the correct amplitude of mixed signal to be manipulated by Stage 8, set according to the application.

Stage 8 is used to manipulate the Information Signal by controlled compression. E e amplitude of the mixed E.G.S. controls the amount of compression,whereby a reduction in E.G.S. amplitude results in an increase of compression on the Information Signal.

Stage 9 can also be used to manipulate the Information Signal by giving a 20dB/decade lift to higher frequencies,if required, or form a 1st order low pass filter with a cut off frequency set at the upper limit of the stated range of Information Signal frequencies.Finally Stage 10 contains power amplification circuitry to drive the output transducers which convert the manipulated Information Signal back into sound waves,but which do not respond to the E.G.S.These transducers usually being headphones.

Specific embodiments of the invention will now be described by way of example with reference to the accompanying system block diagram Fig.l.

Example 1 -An electronic hearing aid for defective human hearing.

Referring to Fig.l,the microphone and amplification circuitry of Stage 1 is set to give an omni-directional sensitivity approaching that of normal human hearing.

Stage 2 V.C.A. circuitry is set to give a x2 gain to the Information Signal unless it recieves a control signal from Stage 3.When this control signal is recieved the above gain of the Stage 2 circuitry is reduced by approx. 10%.This reduction in gain is used to increase the dynamic range of the hearing aid in very loud environments,thus helping to prevent saturation of any of the circuitry.

Stage 3 circuitry is thus set up to produce a 'reduce gain' control signal when the Information Signal amplitude from Stage 1 exceeds the threshold which would cause saturation and thereby distort the Information Signal.

Stage 4 E.G.S. circuitry generates a sine wave tone of a frequency which is both above the highest audible frequencies and also above the highest frequency which the output transducers can respond to,i.e. at the upper limit of the stated range.

Stage 5 V.C.A. circuitry is used to give two levels of sine wave tone depending on the control signal from Stage 6.These levels are a reduction of the amplitude of the tone,level l,and a 7Q% reduction ,level 2,when the control signal has been activated.

Stage 6 monitor circuitry gives a switching control signal depending on two thresholds.The first static threshold is set at the level at which the Information Signal is sufficient to prevent excessive amplification of circuit noise by Stage 8.The second dynamic threshold represents the average level of the Information Signal i. e. the level of the background sounds. If the instantaneous amplitude of the Information Signal exceeds these thresholds Stage 6 produces a 'reduce tone level' control signal, switching the tone from level 1 to level 2.

Stage 7 mixing circuitry combines the Information Signal and sine wave tone signal in the correct proportions and at the correct amplitudes in order to enhance the use of the properties of Stage 8 circuitry.

The Mixed Signal leaving Stage 7 contains the sine wave tone,at level 1 from Stage 5,with an amplitude which is 50% of the level of maximum compression of the Stage 8 circuitry.This Mixed Signal also contains the Information Signal, which has an amplitude such that normal conversation in a quiet environment produces a Mixed Signal,leaving Stage 7,which is approximately 3% above the level of maximum compression.

Stage 8 compression circuitry tends to maintain its output at a constant level Thus when only background sounds are present the gain is relatively high,limited by the amplitude of the tone.However,when sounds of higher amplitude are present the gain is reduced in order to maintain the output at a constant level.Therefore,due to the drop in gain the background sounds have been relatively reduced in the output signal from Stage 8. Thus as a conversation involving an 4d user produces relatively high amplitude sounds the process of compression will tend to diminish the background sounds present in the Information Signal. If the amplitude of the tone is reduced the compression of the Information Signal is increased thus excentuating the relative reduction in the amplitude of the background sounds.

Stage 9 circuitry gives a 20dB/decade lift in frequencies starting at 3.5kHz and rolling off -20dB/decade at 18kHz.This is done in order to compensate for a loss in frequency response-due to defective hearing.

Stage 10 output circuitry produces the output power necessary to drive the transducers which convert the manipulated Information Signal back into sound waves.

Example 2 -This illustrates the invention being used to amplify sounds which are low in amplitude,tending towards The limit of normal human hearing. The system incorporates automatic protection against unexpected high amplitude sounds to prevent damage to the tearing of the user.

Referring to Fig.l,the microphone and amplification circuitry of Stage 1 is set to give a greater sensitivity than that of normal human hearing, the gain being dependant on the application.The microphone transducer can either be omni-directional or uni-directional,as required.

Under the control of the Stage 3 switching signal Stage 2 V.C.A. circuitry reduces its gain significantly in order to prevent circuit saturation due to the high sensitivity of Stage 1.

The 'reduce gain' control signal is produced by Stage 3 monitoring circuitry if the Information Signal amplitude exceeds The threshold at which saturation would have taken place.

Stage 4 E.G.S. circuitry produces a sine wave tone of a frequency which is above the highest frequencies present in the stated range of the Information Signal.

Stage 5 V.C.A. circuitry reduces the tone amplitude by approximately 60%, from level 1 to level 2,when it recieves the 'reduce tone level' control signal from Stage 6.

Stage 6 circuitry produces a 'reduce tone level' control signal when the Information Signal from Stage 2 via path b) is sufficiently high in amplitude to prevent excessive amplification of circuit noise by Stage 8.

Stage 7 circuitry mixes the Information Signal and sine wave tone in the correct proportions.When the Information Signal is at its usual level and the tone amplitude is at level 1 The amplitude of the resultant Mixed Signal will be at least 3% above the level of maximum compression of the Stage 8 circuitry. If no Information Signal is present the Mixed Signal amplitude will be 50% of the level of maximum compression.

Due to the high sensitivity of the Stage 1 circuitry the output circuitry of Stage 10 would be susceptable to abnormally high Information Signal levels.However, the action of the Stage 8 compression circuitry tends to maintain its output signal at a constant level ; thus protecting the Stage 10 circuitry and user from potential damage.

Stage 9 circuitry forms a 1st order low pass filter with a cut off frequency set at the upper limit of the stated range.

Example 3 -This illustrates the invention being used to protect human hearing in environments where there are constant loud amplitude background sounds.The system permits communication in such environments.

Referring to Fig.l,Stage 1 microphone and amplification circuitry are set to give an ozni-directional sensitivity which is lower than that of normal human hearing.

Stage 2 V.C.A. circuitry increases its gain on the Information Signal when it recieves an 'increase gain' control signal from Stage 3.

Stage 3 monitoring circuitry produces an 'increase gain' control signal when The average amplitude of the Information Signal from Stage 1 drops significantly from its normal level.

Stage 4 E.G.S. circuitry produces a sine wave tone of a frequency which is above the highest frequencies in the stated range of the Information Signal.

Stage 5 V.C.A. circuitry reduces its gain by 6056,from level 1 to level 2, when it recieves a 'reduce tone level' control signal from Stage 6.

Stage 6 produces a'reduce tone level' control signal when the amplitude of the instantaneous Information Signal ,from Stage 2 via path b),is sufficiently greater than the average level of the Information Signal.

Stage 7 circuitry mixes the Information Signal and sine wave tone in the correct proportions.If no Information Signal is present and the tone is at level 1 the amplitude of the resultant Mixed Signal will be at least 5% abuse the level of maximum compression of the Stage 8 circuitry.When The constant background sounds are the highest amplitude signal in the Information Signal The resultant Mixed Signal amplitude will be approximately twice the level of maximum compression by Stage 8. Stage 8 circuitry relatively attenuates the Information Signal when only constant background sounds are present by the use of a high amplitude tone controlling the compression process.-7hen sounds of a sufficiently higher amplitude than the background sounds are present in the Information Signal the amplitude of the tone is reduced,from level 1 to level 2, thus increasing the compression of the Information Signal.This has the effect of accentuating the higher amplitude sounds in the output signl from Stage 8.

Stage 9 circuitry forms a 1st order low pass filter with a cut off frequency set at the upper limit of the stated range of Information Signal frequencies.

Stage 10 circuitry drives the manipulated Information Signal into appropriate transducers which convert it back into sound waves.

Claims

1. An electronic hearing aid whereby sound waves are converted into an electrical Information Signal,which is subsequently subjected to controlled compression.The compression being under the control of the amplitude of an Electronically Generated Signal,which contains only frequencies that are above those of the stated range of the Information Signal frequencies. This stated range being dependant on the application.

2. An electronic hearing aid as claimed in claim 1 wherein the Electronically Generated Signal is a sine wave tone of a single frequency which is above the stated range of Information Signal frequencies.

3. An electronic hearing aid as claimed in claim 1 or claim 2 wherein sound waves are converted into an electrical Information Signal using a transducer to give required directionality and subsequent appropriate amplification circuitry to give required sensitivity.

4. An electronic hearing aid as claimed in claim 1 or claim 2 or claim 3 wherein sound waves are converted into an electrical Information Signal andean Electronically Generated Signal is added to form a Mixed Signal.

This Mixed Signal then being subjected to compression.

3. An electronic hearing aid as claimed in claim 4 wherein the Compressed Mixed Signal is filtered,to reduce the Electronically Generated Signal amplitude,and then converted,by means of a suitable transducer,back into sound waves.Thes--transducers being driven by appropriate power amplification.

6. An electronic hearing aid as claimed in claim 5 wherein the amplitude of the Electronically Generated Signal is varied in order to control the amount of compression experienced by the Information Signal.

7. An electronic hearing aid as claimed in claim 5 or claim 6 wherein the Compressed Mixed Signal is given a 20dB/decade lift to frequencies above 3.5kHz with a -20d3/decade roll off from l8kHz,if required for the application.

8. An electronic hearing aid as claimed in any previous claim wherein the amplitude of the Information 3ignal is reduced if it approaches that of the level at which circuit saturation and resultant distortion would occur.

9. An electronic hearing aid substantially as described herein with reference to Fig.l of the accompanying block diagram.