CA1261959A - Automatic gain control for hearing aid - Google Patents
Automatic gain control for hearing aidInfo
- Publication number
- CA1261959A CA1261959A CA000516047A CA516047A CA1261959A CA 1261959 A CA1261959 A CA 1261959A CA 000516047 A CA000516047 A CA 000516047A CA 516047 A CA516047 A CA 516047A CA 1261959 A CA1261959 A CA 1261959A
- Authority
- CA
- Canada
- Prior art keywords
- signal
- gain
- duration
- hearing aid
- microphone
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R25/00—Deaf-aid sets, i.e. electro-acoustic or electro-mechanical hearing aids; Electric tinnitus maskers providing an auditory perception
- H04R25/35—Deaf-aid sets, i.e. electro-acoustic or electro-mechanical hearing aids; Electric tinnitus maskers providing an auditory perception using translation techniques
- H04R25/356—Amplitude, e.g. amplitude shift or compression
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03G—CONTROL OF AMPLIFICATION
- H03G3/00—Gain control in amplifiers or frequency changers without distortion of the input signal
- H03G3/20—Automatic control
- H03G3/30—Automatic control in amplifiers having semiconductor devices
- H03G3/32—Automatic control in amplifiers having semiconductor devices the control being dependent upon ambient noise level or sound level
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03G—CONTROL OF AMPLIFICATION
- H03G7/00—Volume compression or expansion in amplifiers
- H03G7/002—Volume compression or expansion in amplifiers in untuned or low-frequency amplifiers, e.g. audio amplifiers
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03G—CONTROL OF AMPLIFICATION
- H03G9/00—Combinations of two or more types of control, e.g. gain control and tone control
- H03G9/02—Combinations of two or more types of control, e.g. gain control and tone control in untuned amplifiers
- H03G9/025—Combinations of two or more types of control, e.g. gain control and tone control in untuned amplifiers frequency-dependent volume compression or expansion, e.g. multiple-band systems
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R2225/00—Details of deaf aids covered by H04R25/00, not provided for in any of its subgroups
- H04R2225/41—Detection or adaptation of hearing aid parameters or programs to listening situation, e.g. pub, forest
Landscapes
- Engineering & Computer Science (AREA)
- Multimedia (AREA)
- Health & Medical Sciences (AREA)
- General Health & Medical Sciences (AREA)
- Neurosurgery (AREA)
- Otolaryngology (AREA)
- Physics & Mathematics (AREA)
- Acoustics & Sound (AREA)
- Signal Processing (AREA)
- Tone Control, Compression And Expansion, Limiting Amplitude (AREA)
- Control Of Amplification And Gain Control (AREA)
Abstract
TITLE
AUTOMATIC GAIN CONTROL FOR HEARING AID
APPLICANT
TELEX COMMUNICATIONS INC.
INVENTOR
David Allen HOTVET
ABSTRACT
A hearing aid having signal compression characteristics that adapt to the evironment of the sound field in which it is operative in which an automatic gain control signal processor is responsive to the magnitude, duration and frequency of the signals in a sound field to control a compression amplifier so that the gain thereof is proportional to said signals. Fig. 1.
AUTOMATIC GAIN CONTROL FOR HEARING AID
APPLICANT
TELEX COMMUNICATIONS INC.
INVENTOR
David Allen HOTVET
ABSTRACT
A hearing aid having signal compression characteristics that adapt to the evironment of the sound field in which it is operative in which an automatic gain control signal processor is responsive to the magnitude, duration and frequency of the signals in a sound field to control a compression amplifier so that the gain thereof is proportional to said signals. Fig. 1.
Description
1~6'L9~3 BACKGR0~ 2~ J~ r- ON
1. Field of ~he Invention ~ his invention relates to hearing aid~ and i~ ~ore particularly directed to the automatic control o~ hearing aids to enhanc~ tha op~ration under pre~ently dif~icult condition~ enaounter~d by a uoer ~ or exa~pls, rec2iving CO~MUnic~tiOn ~ro~ a ~ourc~ of ~ound located clo~e ~o th3 u~r but 3urroundQd by a ~ultiplicity of oth~r ~ourcos of ~ou~d, ~ in ~ crowdQd roo~ with nu~erou~ convox~tion~ ~nd extr~neou~ "noise" of varying ~ound 1QV~ nd occurring at varying di~tance~ ~rom the user ~ a h~aring aid.
n~ Ar~
~ he prior art with which thi~ i~ention i~ concerned range fro~ r~l~tiv~ly ~imple hearing aid in~truments, which ~ay contain what h~v~ co~e to be known as agc, "co~pres io~" or ~uto~atic g~in control ~ea~ures, and which may also requlre a user to physically manipulate a olu~e control ~o ~ to co~pensate ~or variations in the ~ound fi~ld in~which ~ hsari~g aid instrument i~ operated or ~ay, a~ is ~hown in:U.S. Patent No. 4,461,025~issued July 17, 1984, include~complicated circuitry for :
co~pletely~ellmlnating the background "noise" components ~ ~ -o~ a sound f~eld that are typically characteri~ed as "noise" in~the sen~e that the user of a hearing aid instru~ent do~s not de~i~e to receive, or perceive, such componen~s o~ a signal, ~ Prior art hearing aid instruments have uti.lized compression circuits for reducing output distortion as the total input signal exceeds the maximum capability of a hearing aid instrument system and this i9 accomplished -qt~,.7 ,, ~.
- : .
,' ' ~ " : ,,'''''' ; `: .. .. .
~ ' : :
'~:
.
95~3 by utillzlng a typical rorDl o~ ~uto~natic gain control circuit to ~li~inat~ the accompanying distortion when an exc~s ivæ input ~3 lgn~ ncountered .
on~ ~UC21 autoD~tic g2lin control for this purpose is de~ignad to e~ect a g~ rQductlon during a relatively f~hort: ti~ne intorv~l, that i~ known ~ the "attack ti~e", to pr~vent di~co~ort or annoyanc~ to the u~er of the hearing aid instru3l~Qnl: dus to an e3ccee~iv6~ ~ignal. on the other ~snd, when thæ ~XC:Q8~iV~ ignal i5 no longer prQse~nt or di~inished, it ~y b~ d~f3irabl~s to have a short or ~ long r~l~as~ t~ , dep~rld~nt upon the ~viron~ntal con~ltion~a in which th~ h~aring ~id in~trum~nt 1~ u~, ana th~ ch~r~ctori~tic~ o~ the input signal. qh~ t attack ti~ae, typically 1~:3 than ten ~llli~ocond~, haE~ ~Qn deter~in~d to bQ reasonable whar~a~ a typic:al r5~1~A~ m~ ~y vary îrom ten n~illi~econ~ to ~uch gr~ter int~rval~3 of ti~e.
The aural p~rceptioJl of thQ hll3aring aid u~er i~
influenced by the rlalea~e tiT~.
~IEF l~ ~TION OF mE INVENTXC)N
.
. . l~y invention provid~s~ a haaring: aid apparatus having an auto~a~ic gain c:ontrol signal gor controlllng the gain of al compre~sion ~EIplifior which pro~ide~ a uniform, "fa~t attack5' timQ in r~e~;pon~ to ~n input ~3ignal exce~din5~ a pred6~tQrmined maximum value and a variable ~'rel~a~ tim~ rQ~pon6ive to ad~pl; to th~ various type of signals in the ~ound ~ields encountered by a hearing aid : u~er.
Broadly, the principles of my invention are provided through the utilization of a signal characterizing means for providing a un~for~ ast attack" characteristic for n aueo~tlc gAIn conteol sigllAl iA regponge to inoreases :
.~ , ' :: .
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o~ the input ~ignal ov~r a predetermined a~aximum value and to provida a "release time" which vari~s in accordance with the ~r~guancy and duratiorl o~ tirne intervals in which the input isignal exceeds such predQtermined value.
It h~ been observed th~t lt~e signal to noise ratio i~ dramatically improved in th~ cla~; of æound fields encountered by ~ typical h~aring aid in~tnlment u~er which contain ~ plurality of ~ource~ o~ sound of an undesired nature, and, in the ~ensQ that a 60und ~ield contain~ a plurality o~E ~ourc:es o~ unde~;irable sound that i~ typic~lly r~arr~d to a~ "noi~" (unin'celligible ~ignal) ~nd will cont~in few~r aomponents of desirable sound that ~ay be convenil3ntly referred to as "intelligible" sound, the perception o~ the user i~
enhanced without havlng to ra~ort to :manual ~nan~pulation of th~ volum~ control ln ~ hsari.ng ald in~trull~ent or to experience the porceptiblo varl~tion~ in 60und inten~ity previously ~ ri~snced in h~aring aid lnstru~ent~ ~
~xhibiting a ~f~st att~ck~ and ~fa t release" time regardl~o~ o~ khe n~tur~ o~ thQ sound conkained in a ~ound fi~ld.
.
In a pr~rr~d ~nd the illu~tratàd e~bodiment of my invention, a voltag~ controIled compres~ion a~plifier is configur~d to r~cQive and r~spond to an automatic gain control ~ignal in the for~ o~ a voltage that i~ derived from th~ signal appearing at the output of the amplifier and which w~ll vary ln accordance with the amount, or magnitude, of the output ~lgnal which exceeds a predetermineh compression thre~hold value. The excessive output signal of the voltage controlled amplifier is 35~3 supplied to vary the gain of th~ amplifier through circuit maan~ including at lea~t a pair of capacitors and a resistor which ~r~ connected to r~ceive the automatic gain control signal deriYed from th~ output o~ the amplifier in such a ~ann~r that an auto~atic ~ain control signal o~ rQlatively short duration i8 operative to, in a ~ensQ, to directly and im~ediataly rQduc~ ~nd then immediately restore tha gain o~ th~ a~plifler; and an automatic gain control signal of longer durat~on may be operative to i~medi~tely reduce the sain of the ampli~ier but will gr~dually r~stoxe the gain of th~ ampli~ier at a rate th~t v~ri~s dir~tly with the duration and frequency o~ the recoived signal and khQ auto~atic gain control ~ignal.
In ~ ~urth~r ~bodi~ant of ~y invention, the ~me me~ns for char~ctsrizing th~ AGC ignal f~r controlling the volt~gu controll~d input a~plifi~r msan~ i~ utilized to receivQ a plurality o~ AGC signal~, one derived from the cutput o~ an input voltAgQ controlled compre~sion pre-a~pli~i~r and ~nother dQrived ~rom the output of a power a~pli~ier to ~e r~pr~entative of the sound power level ~SPL) of the audio ~ignal ~pplied to the auditory sense oryans o~ a hearing ~id in6trum~nt u~r. Again, ~or signAl~ o~ a v~ri~bla fre~uency ~nd/or duration that exceed a pred~ermin~d value~ the release time o~ the AGC
s$gnal controlling tha gain o~ the voltag~ controlled input pre-~mplifier i~ varied ~o as to enhance the output signal appli~d to ~he auditory ~ense organs through an incr2ase in th~ "intelligible" signal-to-'~noise" ratio and therQby improve the perception of the u6er. This may be accomplished through th~ addition of but a few uncomplicated component~ which respond to varying automatic gain control 6ignal level~ and duration~ to characterize the signal~ for controlling the gain of the voltage control input pre-a~pli~ier.
6~g~3 ~- s -~IEF DE~cRI-pl IO~ 0~ THB DRAWïNGS
These and ~urther ol:~ject~ and faature6 of my invent.ion will become apparent upon consideration of the following descriptlon and drawing~ in which:
Figure 1, i~ ~ ~che~aatic and diagrammatic illustration of a hearing aid s~mbodying the principles of ~y invention, Figur~ 2, i8 a falaily o~ Clln~e8 illu~trating the operation o~ th~ drawing o Figuro 1: and Figur~ 3, i~ a bloc:k dingraD~matic and ~ch~matic drawing o~ a hearl ng aid l~y~ Q~II illu~trating a further em~odiment o~ ~ny invention.
Dl :S~ XIO?~ ~:)E T~:E l?R]~FER~ED EMBOI:~IMEN~
Ref~rring to Flgur~ 1 o~ the drawlngs, a diagrammatic and ~ch~mat~ c drawing o~ a ~i~plified hearing 2~id instru~ent lnclud~ a voltaga controlled pr~-ampli~iér 10, a tono oontrol amplifier 26 and an outpu~ power : amplifier 28 ~onnect~d to receive a ~ignaI from a ~icrophone through ~n input conductor 11 connect~d to voltage controll~d a~pli~ier lo, an output conductor 12 : connecting the sutput of voltage controlled gain control ampli~1~r 10 to tone control amplifier 2S and to an AGC
signal source, indicated gene.rally by reference character 14, an output conductor 27 connec~ing the output of tone control ~plifier 26 to the input o~ power amplifier 28 and an output conductor 2~ for connecting the output of amplifier 28 to an earphon~ or receiver.
~ Voltage controlled variable gain control pre-ampli~ier 10 further includ~ a gain control terminal :
..:
-.~ .
~LXd ~;iL. ~3~i~
13 for connection to a ~ource of ~ignal for controlling the gain thereo~ fro~ automatic gain control signal source 14.
Si~nal 60urc~ 14 proYides an output signal on conductor 16 which con~i~ts of a rPctified component of the output ~ignal ~ppearing on output conductor 12, connQcted to amplifier lO, whenever the output level exceeds a pred~t~rmin0d maximum value. Conductor 16 is connactQd through t~rminal ~4 on a ~ignal characteri~er 2b to gain control t~rminal 13 on ~ amplifier lO.
Signal charact~rizer 20 i~ 6hown compri~d of capacltor 21 conn~ctad int~rm~diats t~r~inal 24 and a ground ter~in~l ~nd ~ r~i3tor 23 ~nd capac~tor 22 conn~ct~d in ~erle~ acro~s c~pacitor 21 and ~ntQ~mediate t~r~inal 24 an~ ground termln~l. Capacitor 21 ~nd capacitor 22 ar~ typically o~ sub~tantially dif~erent cap~citance and r~ tor 23 may b~ selec~ed from a range o~ higher ~alu~ to proYlde an incr~a~d ti~ congtant when charging cap~cltor 22.
Re~rring to Figure 3 o~ the drawings, a more elaborat~ repras~nt~tion of ~ h~aring aid instrument is ~h wn including a microphon~ 30 ~nd a raceiver 60 operatively connected through voltage controlled Yariablè
ga~n pr~-ampli~isr 10, tone control ampli~ier 26 and power a~plifier 28.
Gain control amplifier lO has an input terminal ll, connected to microphone 30 through capacitox 32 and conductor 31 and an outpu~ terminal connected to tone control ampli~ier 26 through an output conductor 12, terminal 40, terminal 48, resis~or 50 and capacitor 51.
Tha output of tone control amplifier 26 is ~hown connectsd to power ~mpli~ier 2~ through conductor 27 1 ~ 61~3 capacitor 52 and the output conductor~ 29 of amplifier 28 are connected to term$nals 61 and 63 on a receiver 60.
Terminal 48 i~ connected to ground through a resistor 49 and terminal 40 i8 shown connected to a ~ull wa~e AGC
rectifyiny mQans ~5 (6hown in phantom outline) in voltage controlled variabla gain pre-ampli*ier 10 through capacitor 41, r~iator 42, wipQr 43 on potentiometer 44 and conductor 45.
Signal ch~r~ct~rizer 20 includes the ele~ent~
de~cribed abov~ and i~ ~urth~r connected to t~rminal 64 on output 29 o~ po~er a~pllfier 28 through conductor 74, Schottky diode 73, t~rminal 75, capacitor 70, resi~tor 69, w~per C8 on potentio~at~r 67 ànd resistor 66.
Terminal 64 i8 also conn~cted to ground through capacitor 65.
V~rious portion~ of ~h~ ~pli~i~r~ and circuitry are ~uitably connected to a ~ourc~ of current (not shown) and such connactlng compsnent~ ara not ~urther identi~ied.
Flgure 2 contAin~ a number of curve~ placed over a grid to illu~tr~t~ th~ ~lgnals app~ariny at variou6 portions o~ th~ ~pparatu~ described above. ~Curve 80 represant~ tha ~ound pQWQr~ l~v~l 0~ an ~cou~tical:input Bignal; curv~ 81 repre~e~ts an AGC ~ign~l derived ~rom the output o~ ~n ampli~ier; ~urve 82 represents a component o~ ths AGC ~ign~l in curve 81 a~ derived from the output of an a~pli~ier; curve 83 represent~ a compreesed acou~tical output (SPL1 ~ignal as may be applied to the auditory ~ense organs o~ a u~er: and curve 84 r~pre~ents the perc~ived signal as sensed by the auditory organs o~ a hearing aid user.
As indicated under curve 80, the ~ignal~ are divided into a plurality o~ dis~-rete portions indic~ted by ~2~ 9.~
the letters G through U (inclusive3 ~pplied to the bracket~ appearing under the ~ignal illustrated as curve ~0. ~he vertical axi~ reprssents either voltage, or potential, or sound power level and the horizontal axis represent~ time during which a signal ~ay occur.
The illu~trated ~i~nal character~zer 20 is derived fro~ a d~scription cont~ined in the No~ember 1950 issue o~ Audio Engin2ering, page~ 1~, 19, 69 and 70 in an articl~ ontitled "PQr~ormanc~ ~nd Operation of a N~w ~imiting Ampli~ier" by G.P. Singer--a description o~
recently dQvslop~d broadca t-typ~ limiting amplifier and its characteri3tics undlQr v~r~ou~3 input-signal conditionsl'.
The threshold ~gnitude for initiating operation of the automatic gain control circuit into a compression mod~ of op~rat$on, al~o Xnown a8 th~ "knee" of the compression curve, 18 detQr~ined by the characteristics of 8 giv~n in~tru~ent and the physiological characteristics of ~ us~r. Thi~ may be deter~ined by d2aignQrs o~ hearing aid apparatu~ and i8 ba6ed upon experienca and other data accumulated BO that thQ ~um total of tho entir~ h~aring aid in~trument ~ncluding the auto~atic gain controI circuit,~ i8 satisfactory to present a co~ortable, intelligibla audio signal for perception by the ~udio s~n~e organ~ of a user.
However, a long ~tanding unde~irable operation occurs whenev~r th~ i~put ~ignal ~rom the sound field in which the instrument i8 operable, contains undesireable "noise~, euch a~ in a crowded room wit~ many conver~ation~ taking place, and, depending upon the time constant or reaction time of a given AGC compression control signal, thQ user either experiences perceptions of a rapid ~luctuation in volume, or SPL~ or a continued .. , ~
~`' ' _ 9 decr~a~e in ~ound pre~ur~ output ~o that a ~evere loss o~ int~lligibility i~ parceived and, for mo~t practical purpo~, th~ in3tru~ent i~ rendered ~ubstantially useless.
By applying th0 principle~ oP ~y invention to a hearing ~id in~tru~nt $n controlling tha operation of tha co~pr~ion ~od~ o~ a controllQd gain ~plifier, r~l~tively ~hor~ ~bur~t~ or Wpul~e~" of energy are, in ~ect, ~ub~tanti~lly reducod a~d/or ~li~inated from the r~producad slgn~l applied to th~ audltory ~ense organs of a u~r. ~Int~lligibl~ ~ignals, whlch wh~n co~b~ned with thQ background ~noic~" re~ult in an ov~rall reduction in gain with rQ~p~ct to tha ~xce~ive signal rQceived by a microphon~ but per~it a co~bined ~ignal, hàving enhanced ~ignal to "nolss~ r tlo, to b~ a~plif~ed within the r2gi~e o~ a p~r~ ible ~ound psw~r level ~o that a gr~ater proportion o~ th~ ~ignal applied to thQ audio sen~ organ~ o~ ~ u~r consi~t~ of th~ "intelligible"
co~ponont and th~ pr~iou~ly o~tained perception o~ a 1088 Or intalligibillty or oth~r ~or~ o~ di~comfort is ~li~inatsd and th~ u~er i~hsr~by better ~ble to undorstand wh~t ho i~ o~eXlng to hear.
In th~ ~urvæ~ of FigurQ 2, ~n input ~ignal ~hown on tha curve ao contain~ ~ number of components variable about thQ z~ro axi~ and ~hown in relation to ~i pair o~
hor$zont~1 dotted line~ which indicate the maximum level of ~nergy that may rea~onably be accommodated by the electrical a~plifi~r~ of a hearing aid without producing di~ortion.
The lnitial section, G, represents random or backgrou~d no~ee; sections H,J,L,N, and P represent "noise" pulses and s4ctions ~ and T represent ' -- . .
, , 9.S9 ~ 10 --intslligiblQ ~ound Qnorgy. Whenever th~ ~ignal r~pr~entod by curv~ 80 excQed~ the maximum values indicat~d by the dott~d horizontal lines, th~ voltage or pot~ntial app~aring ~t capacitors 21 and 22 will be a~f~ctad in th~ ~annQr ~hown in curve~ 81 and 82 to provid~ a tran~ient AGC ~ign~l that produce~ tha output illu~trated on curve 83 which is then parceived by a hearing ~id us~r as illu~tratad on curve 84.
Whsn con~dering a p~riod of r~ndom or background nol~ in Section G of tha curv~ followed by a pulse of noise of l~s than 12 ~illi6econd~, the relation~hips as illu~trat~d-by ~ectlon H on th~ remainder o~ the curves ar~ obtain~d, th~ ~G~ ~ignal ~or controllin~ the compr3~sion a~pli~i~r i~ such that compres~ion ~o the ~axl~u~ do~r~d li~it~ a~ ~llu~tratad on curve 83 occurs and th~ ~nois~N pul~e re~ain~ unpQrcQived by the hearing ai~ u~er.
When a ~eri~ o~ ~U1B~ ~llu~trat~d by Sections J~No ~nd P arQ r~c~iv~, th~ characterized control signal app~arlng ~h~r~under on GUrVC 81 i8 obtained and thQ rel~tion~h~p~ ~r~ n in ~he remai~der o~ the CUrV~B. Si~ilarly, the ~intelligiblQn-~ignal o~ portions R and ~ Or curv~ 80 r~ult in the phenomina shown in curv~ 81,82,83, and 84.
~ errlns speci~lc~lly to SectionB J-Q (inclusive) o~ the curve; it m~y bs #~en that when a plurality of relatively c108~1y ~paced pulses are received, curve 81 indicates that capacitor 21 acquires a voltage or potential that increa~es in ~teps to serve as the compress~on control ~ignal for the amplifier whereby instead of having a succes~ive plurality o~ compression control slgnal as reprqsented in Section H of curve 81, , ~
A ^_ .
95~3 the poltentizll r1 ~ses in ~t~p~ that ar~ imperceptible l:o the hearing aid user and thereby do not present a source of conru~ion r~sulting ~rom the ~uccss~ive "nois~" pulses o~ Section~ J,L,~, and ~ o~ tha ~ignal shown on curve 80.
When the relatively longer duration of an "intelligibl~n E;ignal appQars, as in Sections R and T of 'chs curve o~ Figurs 80, capacitors 21 and 22 are charged as shown on curves 81 and 82 resp~c:tively, th~ output signal of curv~ 83 i8 compres~d to the desired value and the percaption o~ the h~aring aid us~r i~ as ~hown on cur-~ 84.
In an op~rative elobodiDIent of ~y invention cornpxe~sion ampli~ier lO comprised a commercially ~vail~ble LC/LD No. 502, low distortion, AGC Co~pression Prea~Dpli~i~r ~uppli~ ~ro~ Linear ~chnology Inc. of ~urlington, ont~rio, Canada I.7R 3Y3 W~18 ukil~zed in connection with a ~lgnal charact~rizer having values of 0.~7 D~ ro~aradEI for cap~citor 21, 2.2 ~nicrof~r~ds ~or cap~citor 22 and 220~ oh~ ~or re~i~tor 23.
In th~ ~bodi~t o~ Figure 3, an ~GC-co~pres~ion co~ponent i~ ~dd~d ~rom output 29 on power amplifi~r 28 in which r~si~tor 67 i~ ~ lOX ohm potentiometer, resistor 69 i8 a 3.3K oh~ resistor, càpa~itor 70 is a 2.2 micro~arad capacitor, rasistor~ 71 and 72 are 220K ohm resi~tors and diod~ 73 i~ a Scho~key diode exhibiting the char~cteristic~ o~ a low forward voltage drop and rectification o~ the signal appearing at output 29 repr~sentativQ o the sound pressure level output that is to be applied to the auditory sense organ of a user through ~icrophone 60. While the operation of signal c~aracterizer 20 remain~ essentially the same, it may be seen ~hat what i~ known as "Input" and "output"
, l53~ :3 compression are utilized to form -the signal that appears at terminal 24 on signal characterizer 20 and the opera-tion remains essentially the same as that described above in connection with the curves of Figure 2.
, , : ~ .
: ' ' ' ;
: : : ~
~ ~ .
;
- -- -- -:~.
1. Field of ~he Invention ~ his invention relates to hearing aid~ and i~ ~ore particularly directed to the automatic control o~ hearing aids to enhanc~ tha op~ration under pre~ently dif~icult condition~ enaounter~d by a uoer ~ or exa~pls, rec2iving CO~MUnic~tiOn ~ro~ a ~ourc~ of ~ound located clo~e ~o th3 u~r but 3urroundQd by a ~ultiplicity of oth~r ~ourcos of ~ou~d, ~ in ~ crowdQd roo~ with nu~erou~ convox~tion~ ~nd extr~neou~ "noise" of varying ~ound 1QV~ nd occurring at varying di~tance~ ~rom the user ~ a h~aring aid.
n~ Ar~
~ he prior art with which thi~ i~ention i~ concerned range fro~ r~l~tiv~ly ~imple hearing aid in~truments, which ~ay contain what h~v~ co~e to be known as agc, "co~pres io~" or ~uto~atic g~in control ~ea~ures, and which may also requlre a user to physically manipulate a olu~e control ~o ~ to co~pensate ~or variations in the ~ound fi~ld in~which ~ hsari~g aid instrument i~ operated or ~ay, a~ is ~hown in:U.S. Patent No. 4,461,025~issued July 17, 1984, include~complicated circuitry for :
co~pletely~ellmlnating the background "noise" components ~ ~ -o~ a sound f~eld that are typically characteri~ed as "noise" in~the sen~e that the user of a hearing aid instru~ent do~s not de~i~e to receive, or perceive, such componen~s o~ a signal, ~ Prior art hearing aid instruments have uti.lized compression circuits for reducing output distortion as the total input signal exceeds the maximum capability of a hearing aid instrument system and this i9 accomplished -qt~,.7 ,, ~.
- : .
,' ' ~ " : ,,'''''' ; `: .. .. .
~ ' : :
'~:
.
95~3 by utillzlng a typical rorDl o~ ~uto~natic gain control circuit to ~li~inat~ the accompanying distortion when an exc~s ivæ input ~3 lgn~ ncountered .
on~ ~UC21 autoD~tic g2lin control for this purpose is de~ignad to e~ect a g~ rQductlon during a relatively f~hort: ti~ne intorv~l, that i~ known ~ the "attack ti~e", to pr~vent di~co~ort or annoyanc~ to the u~er of the hearing aid instru3l~Qnl: dus to an e3ccee~iv6~ ~ignal. on the other ~snd, when thæ ~XC:Q8~iV~ ignal i5 no longer prQse~nt or di~inished, it ~y b~ d~f3irabl~s to have a short or ~ long r~l~as~ t~ , dep~rld~nt upon the ~viron~ntal con~ltion~a in which th~ h~aring ~id in~trum~nt 1~ u~, ana th~ ch~r~ctori~tic~ o~ the input signal. qh~ t attack ti~ae, typically 1~:3 than ten ~llli~ocond~, haE~ ~Qn deter~in~d to bQ reasonable whar~a~ a typic:al r5~1~A~ m~ ~y vary îrom ten n~illi~econ~ to ~uch gr~ter int~rval~3 of ti~e.
The aural p~rceptioJl of thQ hll3aring aid u~er i~
influenced by the rlalea~e tiT~.
~IEF l~ ~TION OF mE INVENTXC)N
.
. . l~y invention provid~s~ a haaring: aid apparatus having an auto~a~ic gain c:ontrol signal gor controlllng the gain of al compre~sion ~EIplifior which pro~ide~ a uniform, "fa~t attack5' timQ in r~e~;pon~ to ~n input ~3ignal exce~din5~ a pred6~tQrmined maximum value and a variable ~'rel~a~ tim~ rQ~pon6ive to ad~pl; to th~ various type of signals in the ~ound ~ields encountered by a hearing aid : u~er.
Broadly, the principles of my invention are provided through the utilization of a signal characterizing means for providing a un~for~ ast attack" characteristic for n aueo~tlc gAIn conteol sigllAl iA regponge to inoreases :
.~ , ' :: .
'' , 9 ,~
-- 3 ~
o~ the input ~ignal ov~r a predetermined a~aximum value and to provida a "release time" which vari~s in accordance with the ~r~guancy and duratiorl o~ tirne intervals in which the input isignal exceeds such predQtermined value.
It h~ been observed th~t lt~e signal to noise ratio i~ dramatically improved in th~ cla~; of æound fields encountered by ~ typical h~aring aid in~tnlment u~er which contain ~ plurality of ~ource~ o~ sound of an undesired nature, and, in the ~ensQ that a 60und ~ield contain~ a plurality o~E ~ourc:es o~ unde~;irable sound that i~ typic~lly r~arr~d to a~ "noi~" (unin'celligible ~ignal) ~nd will cont~in few~r aomponents of desirable sound that ~ay be convenil3ntly referred to as "intelligible" sound, the perception o~ the user i~
enhanced without havlng to ra~ort to :manual ~nan~pulation of th~ volum~ control ln ~ hsari.ng ald in~trull~ent or to experience the porceptiblo varl~tion~ in 60und inten~ity previously ~ ri~snced in h~aring aid lnstru~ent~ ~
~xhibiting a ~f~st att~ck~ and ~fa t release" time regardl~o~ o~ khe n~tur~ o~ thQ sound conkained in a ~ound fi~ld.
.
In a pr~rr~d ~nd the illu~tratàd e~bodiment of my invention, a voltag~ controIled compres~ion a~plifier is configur~d to r~cQive and r~spond to an automatic gain control ~ignal in the for~ o~ a voltage that i~ derived from th~ signal appearing at the output of the amplifier and which w~ll vary ln accordance with the amount, or magnitude, of the output ~lgnal which exceeds a predetermineh compression thre~hold value. The excessive output signal of the voltage controlled amplifier is 35~3 supplied to vary the gain of th~ amplifier through circuit maan~ including at lea~t a pair of capacitors and a resistor which ~r~ connected to r~ceive the automatic gain control signal deriYed from th~ output o~ the amplifier in such a ~ann~r that an auto~atic ~ain control signal o~ rQlatively short duration i8 operative to, in a ~ensQ, to directly and im~ediataly rQduc~ ~nd then immediately restore tha gain o~ th~ a~plifler; and an automatic gain control signal of longer durat~on may be operative to i~medi~tely reduce the sain of the ampli~ier but will gr~dually r~stoxe the gain of th~ ampli~ier at a rate th~t v~ri~s dir~tly with the duration and frequency o~ the recoived signal and khQ auto~atic gain control ~ignal.
In ~ ~urth~r ~bodi~ant of ~y invention, the ~me me~ns for char~ctsrizing th~ AGC ignal f~r controlling the volt~gu controll~d input a~plifi~r msan~ i~ utilized to receivQ a plurality o~ AGC signal~, one derived from the cutput o~ an input voltAgQ controlled compre~sion pre-a~pli~i~r and ~nother dQrived ~rom the output of a power a~pli~ier to ~e r~pr~entative of the sound power level ~SPL) of the audio ~ignal ~pplied to the auditory sense oryans o~ a hearing ~id in6trum~nt u~r. Again, ~or signAl~ o~ a v~ri~bla fre~uency ~nd/or duration that exceed a pred~ermin~d value~ the release time o~ the AGC
s$gnal controlling tha gain o~ the voltag~ controlled input pre-~mplifier i~ varied ~o as to enhance the output signal appli~d to ~he auditory ~ense organs through an incr2ase in th~ "intelligible" signal-to-'~noise" ratio and therQby improve the perception of the u6er. This may be accomplished through th~ addition of but a few uncomplicated component~ which respond to varying automatic gain control 6ignal level~ and duration~ to characterize the signal~ for controlling the gain of the voltage control input pre-a~pli~ier.
6~g~3 ~- s -~IEF DE~cRI-pl IO~ 0~ THB DRAWïNGS
These and ~urther ol:~ject~ and faature6 of my invent.ion will become apparent upon consideration of the following descriptlon and drawing~ in which:
Figure 1, i~ ~ ~che~aatic and diagrammatic illustration of a hearing aid s~mbodying the principles of ~y invention, Figur~ 2, i8 a falaily o~ Clln~e8 illu~trating the operation o~ th~ drawing o Figuro 1: and Figur~ 3, i~ a bloc:k dingraD~matic and ~ch~matic drawing o~ a hearl ng aid l~y~ Q~II illu~trating a further em~odiment o~ ~ny invention.
Dl :S~ XIO?~ ~:)E T~:E l?R]~FER~ED EMBOI:~IMEN~
Ref~rring to Flgur~ 1 o~ the drawlngs, a diagrammatic and ~ch~mat~ c drawing o~ a ~i~plified hearing 2~id instru~ent lnclud~ a voltaga controlled pr~-ampli~iér 10, a tono oontrol amplifier 26 and an outpu~ power : amplifier 28 ~onnect~d to receive a ~ignaI from a ~icrophone through ~n input conductor 11 connect~d to voltage controll~d a~pli~ier lo, an output conductor 12 : connecting the sutput of voltage controlled gain control ampli~1~r 10 to tone control amplifier 2S and to an AGC
signal source, indicated gene.rally by reference character 14, an output conductor 27 connec~ing the output of tone control ~plifier 26 to the input o~ power amplifier 28 and an output conductor 2~ for connecting the output of amplifier 28 to an earphon~ or receiver.
~ Voltage controlled variable gain control pre-ampli~ier 10 further includ~ a gain control terminal :
..:
-.~ .
~LXd ~;iL. ~3~i~
13 for connection to a ~ource of ~ignal for controlling the gain thereo~ fro~ automatic gain control signal source 14.
Si~nal 60urc~ 14 proYides an output signal on conductor 16 which con~i~ts of a rPctified component of the output ~ignal ~ppearing on output conductor 12, connQcted to amplifier lO, whenever the output level exceeds a pred~t~rmin0d maximum value. Conductor 16 is connactQd through t~rminal ~4 on a ~ignal characteri~er 2b to gain control t~rminal 13 on ~ amplifier lO.
Signal charact~rizer 20 i~ 6hown compri~d of capacltor 21 conn~ctad int~rm~diats t~r~inal 24 and a ground ter~in~l ~nd ~ r~i3tor 23 ~nd capac~tor 22 conn~ct~d in ~erle~ acro~s c~pacitor 21 and ~ntQ~mediate t~r~inal 24 an~ ground termln~l. Capacitor 21 ~nd capacitor 22 ar~ typically o~ sub~tantially dif~erent cap~citance and r~ tor 23 may b~ selec~ed from a range o~ higher ~alu~ to proYlde an incr~a~d ti~ congtant when charging cap~cltor 22.
Re~rring to Figure 3 o~ the drawings, a more elaborat~ repras~nt~tion of ~ h~aring aid instrument is ~h wn including a microphon~ 30 ~nd a raceiver 60 operatively connected through voltage controlled Yariablè
ga~n pr~-ampli~isr 10, tone control ampli~ier 26 and power a~plifier 28.
Gain control amplifier lO has an input terminal ll, connected to microphone 30 through capacitox 32 and conductor 31 and an outpu~ terminal connected to tone control ampli~ier 26 through an output conductor 12, terminal 40, terminal 48, resis~or 50 and capacitor 51.
Tha output of tone control amplifier 26 is ~hown connectsd to power ~mpli~ier 2~ through conductor 27 1 ~ 61~3 capacitor 52 and the output conductor~ 29 of amplifier 28 are connected to term$nals 61 and 63 on a receiver 60.
Terminal 48 i~ connected to ground through a resistor 49 and terminal 40 i8 shown connected to a ~ull wa~e AGC
rectifyiny mQans ~5 (6hown in phantom outline) in voltage controlled variabla gain pre-ampli*ier 10 through capacitor 41, r~iator 42, wipQr 43 on potentiometer 44 and conductor 45.
Signal ch~r~ct~rizer 20 includes the ele~ent~
de~cribed abov~ and i~ ~urth~r connected to t~rminal 64 on output 29 o~ po~er a~pllfier 28 through conductor 74, Schottky diode 73, t~rminal 75, capacitor 70, resi~tor 69, w~per C8 on potentio~at~r 67 ànd resistor 66.
Terminal 64 i8 also conn~cted to ground through capacitor 65.
V~rious portion~ of ~h~ ~pli~i~r~ and circuitry are ~uitably connected to a ~ourc~ of current (not shown) and such connactlng compsnent~ ara not ~urther identi~ied.
Flgure 2 contAin~ a number of curve~ placed over a grid to illu~tr~t~ th~ ~lgnals app~ariny at variou6 portions o~ th~ ~pparatu~ described above. ~Curve 80 represant~ tha ~ound pQWQr~ l~v~l 0~ an ~cou~tical:input Bignal; curv~ 81 repre~e~ts an AGC ~ign~l derived ~rom the output o~ ~n ampli~ier; ~urve 82 represents a component o~ ths AGC ~ign~l in curve 81 a~ derived from the output of an a~pli~ier; curve 83 represent~ a compreesed acou~tical output (SPL1 ~ignal as may be applied to the auditory ~ense organs o~ a u~er: and curve 84 r~pre~ents the perc~ived signal as sensed by the auditory organs o~ a hearing aid user.
As indicated under curve 80, the ~ignal~ are divided into a plurality o~ dis~-rete portions indic~ted by ~2~ 9.~
the letters G through U (inclusive3 ~pplied to the bracket~ appearing under the ~ignal illustrated as curve ~0. ~he vertical axi~ reprssents either voltage, or potential, or sound power level and the horizontal axis represent~ time during which a signal ~ay occur.
The illu~trated ~i~nal character~zer 20 is derived fro~ a d~scription cont~ined in the No~ember 1950 issue o~ Audio Engin2ering, page~ 1~, 19, 69 and 70 in an articl~ ontitled "PQr~ormanc~ ~nd Operation of a N~w ~imiting Ampli~ier" by G.P. Singer--a description o~
recently dQvslop~d broadca t-typ~ limiting amplifier and its characteri3tics undlQr v~r~ou~3 input-signal conditionsl'.
The threshold ~gnitude for initiating operation of the automatic gain control circuit into a compression mod~ of op~rat$on, al~o Xnown a8 th~ "knee" of the compression curve, 18 detQr~ined by the characteristics of 8 giv~n in~tru~ent and the physiological characteristics of ~ us~r. Thi~ may be deter~ined by d2aignQrs o~ hearing aid apparatu~ and i8 ba6ed upon experienca and other data accumulated BO that thQ ~um total of tho entir~ h~aring aid in~trument ~ncluding the auto~atic gain controI circuit,~ i8 satisfactory to present a co~ortable, intelligibla audio signal for perception by the ~udio s~n~e organ~ of a user.
However, a long ~tanding unde~irable operation occurs whenev~r th~ i~put ~ignal ~rom the sound field in which the instrument i8 operable, contains undesireable "noise~, euch a~ in a crowded room wit~ many conver~ation~ taking place, and, depending upon the time constant or reaction time of a given AGC compression control signal, thQ user either experiences perceptions of a rapid ~luctuation in volume, or SPL~ or a continued .. , ~
~`' ' _ 9 decr~a~e in ~ound pre~ur~ output ~o that a ~evere loss o~ int~lligibility i~ parceived and, for mo~t practical purpo~, th~ in3tru~ent i~ rendered ~ubstantially useless.
By applying th0 principle~ oP ~y invention to a hearing ~id in~tru~nt $n controlling tha operation of tha co~pr~ion ~od~ o~ a controllQd gain ~plifier, r~l~tively ~hor~ ~bur~t~ or Wpul~e~" of energy are, in ~ect, ~ub~tanti~lly reducod a~d/or ~li~inated from the r~producad slgn~l applied to th~ audltory ~ense organs of a u~r. ~Int~lligibl~ ~ignals, whlch wh~n co~b~ned with thQ background ~noic~" re~ult in an ov~rall reduction in gain with rQ~p~ct to tha ~xce~ive signal rQceived by a microphon~ but per~it a co~bined ~ignal, hàving enhanced ~ignal to "nolss~ r tlo, to b~ a~plif~ed within the r2gi~e o~ a p~r~ ible ~ound psw~r level ~o that a gr~ater proportion o~ th~ ~ignal applied to thQ audio sen~ organ~ o~ ~ u~r consi~t~ of th~ "intelligible"
co~ponont and th~ pr~iou~ly o~tained perception o~ a 1088 Or intalligibillty or oth~r ~or~ o~ di~comfort is ~li~inatsd and th~ u~er i~hsr~by better ~ble to undorstand wh~t ho i~ o~eXlng to hear.
In th~ ~urvæ~ of FigurQ 2, ~n input ~ignal ~hown on tha curve ao contain~ ~ number of components variable about thQ z~ro axi~ and ~hown in relation to ~i pair o~
hor$zont~1 dotted line~ which indicate the maximum level of ~nergy that may rea~onably be accommodated by the electrical a~plifi~r~ of a hearing aid without producing di~ortion.
The lnitial section, G, represents random or backgrou~d no~ee; sections H,J,L,N, and P represent "noise" pulses and s4ctions ~ and T represent ' -- . .
, , 9.S9 ~ 10 --intslligiblQ ~ound Qnorgy. Whenever th~ ~ignal r~pr~entod by curv~ 80 excQed~ the maximum values indicat~d by the dott~d horizontal lines, th~ voltage or pot~ntial app~aring ~t capacitors 21 and 22 will be a~f~ctad in th~ ~annQr ~hown in curve~ 81 and 82 to provid~ a tran~ient AGC ~ign~l that produce~ tha output illu~trated on curve 83 which is then parceived by a hearing ~id us~r as illu~tratad on curve 84.
Whsn con~dering a p~riod of r~ndom or background nol~ in Section G of tha curv~ followed by a pulse of noise of l~s than 12 ~illi6econd~, the relation~hips as illu~trat~d-by ~ectlon H on th~ remainder o~ the curves ar~ obtain~d, th~ ~G~ ~ignal ~or controllin~ the compr3~sion a~pli~i~r i~ such that compres~ion ~o the ~axl~u~ do~r~d li~it~ a~ ~llu~tratad on curve 83 occurs and th~ ~nois~N pul~e re~ain~ unpQrcQived by the hearing ai~ u~er.
When a ~eri~ o~ ~U1B~ ~llu~trat~d by Sections J~No ~nd P arQ r~c~iv~, th~ characterized control signal app~arlng ~h~r~under on GUrVC 81 i8 obtained and thQ rel~tion~h~p~ ~r~ n in ~he remai~der o~ the CUrV~B. Si~ilarly, the ~intelligiblQn-~ignal o~ portions R and ~ Or curv~ 80 r~ult in the phenomina shown in curv~ 81,82,83, and 84.
~ errlns speci~lc~lly to SectionB J-Q (inclusive) o~ the curve; it m~y bs #~en that when a plurality of relatively c108~1y ~paced pulses are received, curve 81 indicates that capacitor 21 acquires a voltage or potential that increa~es in ~teps to serve as the compress~on control ~ignal for the amplifier whereby instead of having a succes~ive plurality o~ compression control slgnal as reprqsented in Section H of curve 81, , ~
A ^_ .
95~3 the poltentizll r1 ~ses in ~t~p~ that ar~ imperceptible l:o the hearing aid user and thereby do not present a source of conru~ion r~sulting ~rom the ~uccss~ive "nois~" pulses o~ Section~ J,L,~, and ~ o~ tha ~ignal shown on curve 80.
When the relatively longer duration of an "intelligibl~n E;ignal appQars, as in Sections R and T of 'chs curve o~ Figurs 80, capacitors 21 and 22 are charged as shown on curves 81 and 82 resp~c:tively, th~ output signal of curv~ 83 i8 compres~d to the desired value and the percaption o~ the h~aring aid us~r i~ as ~hown on cur-~ 84.
In an op~rative elobodiDIent of ~y invention cornpxe~sion ampli~ier lO comprised a commercially ~vail~ble LC/LD No. 502, low distortion, AGC Co~pression Prea~Dpli~i~r ~uppli~ ~ro~ Linear ~chnology Inc. of ~urlington, ont~rio, Canada I.7R 3Y3 W~18 ukil~zed in connection with a ~lgnal charact~rizer having values of 0.~7 D~ ro~aradEI for cap~citor 21, 2.2 ~nicrof~r~ds ~or cap~citor 22 and 220~ oh~ ~or re~i~tor 23.
In th~ ~bodi~t o~ Figure 3, an ~GC-co~pres~ion co~ponent i~ ~dd~d ~rom output 29 on power amplifi~r 28 in which r~si~tor 67 i~ ~ lOX ohm potentiometer, resistor 69 i8 a 3.3K oh~ resistor, càpa~itor 70 is a 2.2 micro~arad capacitor, rasistor~ 71 and 72 are 220K ohm resi~tors and diod~ 73 i~ a Scho~key diode exhibiting the char~cteristic~ o~ a low forward voltage drop and rectification o~ the signal appearing at output 29 repr~sentativQ o the sound pressure level output that is to be applied to the auditory sense organ of a user through ~icrophone 60. While the operation of signal c~aracterizer 20 remain~ essentially the same, it may be seen ~hat what i~ known as "Input" and "output"
, l53~ :3 compression are utilized to form -the signal that appears at terminal 24 on signal characterizer 20 and the opera-tion remains essentially the same as that described above in connection with the curves of Figure 2.
, , : ~ .
: ' ' ' ;
: : : ~
~ ~ .
;
- -- -- -:~.
Claims (20)
1. In a hearing aid, a signal processor responsive to the frequency, and energy content of a signal to be processed for compressing a signal when the amplitude is above a predetermined threshold level, comprising in combination; a terminal for connection to a compression amplifier; and a plurality of time constant means connected to said terminal, said time constant means being characterized to provide individual time constants of a diverse character for providing a compression amplifier control signal having a short attach and relatively longer release time, said release time being proportional to the duration of an input signal when the amplitude of said input signal is above said predetermined threshold level.
2. The subject matter of claim 1 in which there are at least first and second time constant means.
3. The subject matter of claim 1 in which the time constant means include a capacitor.
4. The apparatus of claim 1 in which one of the time constant means is a capacitor and the remainder of said time constant means are capacitors connected to the terminal through serial impedance means.
5. A compression control signal processor for a hearing aid instrument comprising, in combination; an input terminal adapted for connection to a source of signal of variable amplitude, duration and frequency of occurance; and a plurality of time constant means connected to said input terminal and responsive to the d.c. components in a signal present at said terminal whereby the potential at said terminal responds at a rapid rate when said source of signal exceeds a predetermined threshold level and is increasing, and at a variable lesser rate/ proportional to the duration of said source of signal when the amplitude of said source of signal is above a predetermined threshold level and said source of signal is decreasing, said variable rate increasing in proportion to the duration of said signal.
6. In combination with a human sound sense organ facility, a compression control for reducing the effect of undesired transient noise; comprising in combination, acoustical sound transducing means for receiving acoustical energy signals;
amplifying means; gain control means exhibiting variable response to said signals proportional to the amplitude, frequency and duration and operable to rapidly compress said signal when the signals are increasing and to release said compression at a relatively slower, variable rate proportional to the duration of said signals when the amplitude of said signals exceeds a predetermined threshold level, and when said signals are decreasing; and transducing means converting the output of said amplifying means for application to the auditory sense organ of a hearing aid user.
amplifying means; gain control means exhibiting variable response to said signals proportional to the amplitude, frequency and duration and operable to rapidly compress said signal when the signals are increasing and to release said compression at a relatively slower, variable rate proportional to the duration of said signals when the amplitude of said signals exceeds a predetermined threshold level, and when said signals are decreasing; and transducing means converting the output of said amplifying means for application to the auditory sense organ of a hearing aid user.
7. In a hearing aid of the class including a receiver and a microphone and amplifying means connecting the output of said microphone to said receiver and said amplifier including means for controlling the gain therof in accordance with the ambient level of sound energy present in the environment of a user, the improvement, comprising in combination; further gain controlling means for said amplifier, said further gain controlling means including means for determining the presence of sound energy in excess of a predetermined level to reduce the gain of said amplifier to a predetermined level, means for immediately reducing the gain of said amplifier to provide an output not in excess of said predetermined level and means for effecting the return of the gain of said amplifier to said ambient level, said last named means including means responsive to the duration of the sound energy in excess of said predetermined level for increasingly variably restoring the gain of said amplifying means in proportion to said duration.
8. The apparatus of claims 7 in which the further gain controlling means exhibits the characteristics of uniform fast attack time response to an excess signal and a relatively slower variable release time proportional to the duration of an excess signal for restoring the gain of the amplifier.
9. The apparatus of claim 8 in which the further gain controlling means exhibiting a plurality of time constants.
10. The apparatus of claim 9 in which a plurality of time constants are provided by plurality of capacitors, all but one of which are serially connected to an impedance means and are selected to exhibit diverse values and time constants.
11. A hearing aid comprising in combination;
a) a microphone;
b) a receiver; and, c) electrical signal amplifying means, including a source of electrical power, connected intermediate said microphone and said receiver, said electrical signal amplifying means including first gain control means responsive to the average level of signal from said microphone and second and third gain controlling means responsive to the signal at said microphone, said second gain controlling means responsive to the signal at said microphone in excess of a predetermined value to reduce the gain of said amplifying means so that the signal at said microphone remains at said predetermined value, said second gain control means being effective as long as said excess signal is present and said third gain controlling means being effective to reduce the gain of said amplifying means in accordance with said second gain controlling means and the frequency and amplitude of the signal exceeding the predetermined value increases, the gain of said amplifying means is controlled by said third gain control means.
a) a microphone;
b) a receiver; and, c) electrical signal amplifying means, including a source of electrical power, connected intermediate said microphone and said receiver, said electrical signal amplifying means including first gain control means responsive to the average level of signal from said microphone and second and third gain controlling means responsive to the signal at said microphone, said second gain controlling means responsive to the signal at said microphone in excess of a predetermined value to reduce the gain of said amplifying means so that the signal at said microphone remains at said predetermined value, said second gain control means being effective as long as said excess signal is present and said third gain controlling means being effective to reduce the gain of said amplifying means in accordance with said second gain controlling means and the frequency and amplitude of the signal exceeding the predetermined value increases, the gain of said amplifying means is controlled by said third gain control means.
12, In combination with a hearing aid having a signal processing variable gain amplifying means including input, gain control and output terminals, said input terminal connected to a source of audio signal and said output terminal connected to a receiver; gain control means connected to said output terminal and responsive to an output signal in excess of a predetermined magnitude for providing a gain control signal related to said excess output signal and signal characterizing means connecting said gain control signal to the gain control terminal on said amplifying means, said signal characterizing means including means operable to provide a further component to very the effective rate of change of a compression signal in accordance with the frequency of occurrence and the energy content of said signal whereby the compression signal has a short attack and a relatively longer release time, said release time further being proportional to the duration of said signal in excess of a predetermined magnitude.
13. The method of reducing the effect of pulses of high amplitude sound energy on the auditory sense organs of a hearing aid user which comprises:
(a) controlling the gain of a hearing aid instrument so that the gain is immediately reduced on the occurrence of a period of high amplitude sound energy and the gain is restored at a slower rate proportional to the duration of said high amplitude sound energy.
(a) controlling the gain of a hearing aid instrument so that the gain is immediately reduced on the occurrence of a period of high amplitude sound energy and the gain is restored at a slower rate proportional to the duration of said high amplitude sound energy.
14. A hearing aid for use under ambient conditions exhibiting the repetitive occurrence of periods of high amplitude sound energy at a random frequency, comprising in combination;
(a) a microphone;
(b) a receiver; and, (c) controllable gain amplifying means connected intermediate said microphone and said receiver, said controllable gain amplifying means including gain control means responsive to the level of the signal from said microphone above a predetermined threshold level for rapidly reducing the gain of said amplifying means and restoring the gain when the signal from said microphone is reduced to said predetermined level and further means connected to said means responsive to the level of said signal for increasing the time for said gain control means to restore the gain in proportion to the duration of a high amplitude sound energy level.
(a) a microphone;
(b) a receiver; and, (c) controllable gain amplifying means connected intermediate said microphone and said receiver, said controllable gain amplifying means including gain control means responsive to the level of the signal from said microphone above a predetermined threshold level for rapidly reducing the gain of said amplifying means and restoring the gain when the signal from said microphone is reduced to said predetermined level and further means connected to said means responsive to the level of said signal for increasing the time for said gain control means to restore the gain in proportion to the duration of a high amplitude sound energy level.
15. An automatic gain control hearing aid characterized by having a short attack time and relatively longer release time said release time being proportional to the duration of an input signal when the amplitude of the signal is above a predetermined threshold level.
16. The subject matter of claim 15 in which the release time is longer for input signals of long duration.
17. The apparatus of claim 6 in which the amplifying means exhibits the characteristics of a type LC/LD No. 502 Linear Technology Inc. AGC compression preamplifier.
18. The apparatus of claim 17 in which the gain control means includes a first capacitor of 0.47 microfarad capacity connected in parallel with a second capacitor of 2.2 microfarad capacity and a resistor of 220,000 ohms.
19. The apparatus of claim 2 in which said first time constant means is a 0.47 microfarad capacitor and said second time constant means is a 2.2 microfarad capacitor connected in series with a 220,000 ohm resistor.
20. The apparatus of claim 8 in which the further gain con-trolling means includes a 2.2 microfarad capacitor and a 220,000 ohm resistor connected in series with a 0.47 microfarad capacitor and the amplifier exhibits the input characteristics of an LC/LD 502 AGC compression amplifier.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/823,668 US4718099A (en) | 1986-01-29 | 1986-01-29 | Automatic gain control for hearing aid |
| US823,668 | 1992-01-21 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1261959A true CA1261959A (en) | 1989-09-26 |
Family
ID=25239370
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000516047A Expired CA1261959A (en) | 1986-01-29 | 1986-08-15 | Automatic gain control for hearing aid |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4718099A (en) |
| EP (1) | EP0231721A3 (en) |
| JP (1) | JPS62180700A (en) |
| AU (1) | AU594071B2 (en) |
| CA (1) | CA1261959A (en) |
| DE (1) | DE231721T1 (en) |
| DK (1) | DK376786A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5909497A (en) * | 1996-10-10 | 1999-06-01 | Alexandrescu; Eugene | Programmable hearing aid instrument and programming method thereof |
Families Citing this family (49)
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1986
- 1986-01-29 US US06/823,668 patent/US4718099A/en not_active Expired - Lifetime
- 1986-08-04 AU AU60853/86A patent/AU594071B2/en not_active Ceased
- 1986-08-07 DK DK376786A patent/DK376786A/en not_active Application Discontinuation
- 1986-08-15 CA CA000516047A patent/CA1261959A/en not_active Expired
- 1986-08-27 JP JP61201213A patent/JPS62180700A/en active Pending
- 1986-08-27 DE DE198686630133T patent/DE231721T1/en active Pending
- 1986-08-27 EP EP86630133A patent/EP0231721A3/en not_active Withdrawn
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5909497A (en) * | 1996-10-10 | 1999-06-01 | Alexandrescu; Eugene | Programmable hearing aid instrument and programming method thereof |
Also Published As
| Publication number | Publication date |
|---|---|
| AU594071B2 (en) | 1990-03-01 |
| EP0231721A2 (en) | 1987-08-12 |
| DK376786A (en) | 1987-07-30 |
| AU6085386A (en) | 1987-07-30 |
| JPS62180700A (en) | 1987-08-07 |
| US4718099B1 (en) | 1992-01-28 |
| US4718099A (en) | 1988-01-05 |
| EP0231721A3 (en) | 1989-05-17 |
| DK376786D0 (en) | 1986-08-07 |
| DE231721T1 (en) | 1987-12-17 |
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