Digital Hearing Aid DSP Chip Parameter Fitting Optimization

Transcription

1 ICCAS005 June -5, KINTEX, Gyeongg-Do, Korea Dgtal Hearng Ad DSP Chp Parameter Fttng Optmzaton Soon Suk Jarng*, You Jung Kwon*, Je Hyung Lee** *Dept. of Informaton, Control & Instrumentaton, Chosun Unversty, South Korea (Tel : ; E-mal: ssjarng@hosun.a.kr) **Dept. of Informaton, Control & Instrumentaton, Chosun Unversty, South Korea (Tel : ; E-mal: emal@mnmay.bz) Abstrat: DSP hp parameters of a dgtal hearng ad (HA) should be optmally seleted or ftted for hearng mpared persons. The more prese parameter fttng guarantees the better ompensaton of the hearng loss (HL). Dgtal HAs adopt DSP hps for more prese fttng of varous HL threshold urve patterns. A spef DSP hp suh as Gennum GB311 was desgned and manufatured n order to math up to about 4.7 bllon dfferent possble HL ases wth ombnaton of 7 lmted parameters. Ths paper deals wth a dgtal HA fttng program whh s developed for optmal fttng of GB311 DSP hp parameters. The fttng program has ompleted features from audogram nput to DSP hp nterfae. The ompensaton effets of the mrophone and the reever are also nluded. The paper shows some applaton examples. Keywords: Dgtal Hearng Ad, GB311 DSP Chp, Parameter Fttng, Optmzaton, Hearng Loss, Audogram 1. INTRODUCTION Hearng mpared persons have nreased HL threshold urves over audo frequeny band, so that ther hearng mparments may be partly ompensated by HAs. Before 1990s analog HAs domnated HA markets even though analog HAs are lmted n the HL ompensaton beause they are not modfable. In analog ITE(In-The-Ear) type HAs a logarthm volume ontrol swth s the only way of modfaton. There were some onventonal fttng formulas developed for better hoe of amplfaton and ompresson [1]. The advent of the sophstated semondutor tehnology as well as the better understandng of the hearng physology opened the age of dgtal HAs last deade. Dgtal HAs are modfable, that s, eah dfferent type of hearng mparment an be presely ompensated wth the same lass of the dgtal HA. These mult-purposed dgtal HAs are possble by adoptng DSP based IC hp desgn and manufaturng. DSP hps for dgtal HAs are dvded nto two ategores; spef DSP hp and general DSP hp. The spef HA DSP hp was produed earler beause the mnature sze of the hp pakage was requred for ITE type HA fabraton []. Reently, general DSP hps are gettng down n pakagng sze wth lower power onsumpton, so as to be appled to ITE type HAs [3, 4]. As dgtal HAs support more funtons and flexbltes, the fttng method of the dgtal HAs beomes mportant ssues n the hearng ad market. Ths paper apples a spef DSP hp suh as Gennum GB311 (Fg. 1) to dgtal HA fabraton and shows the result of the optmal parameter fttng program development for the hp. The man features of GB311 are 4 hannel nonlnear ompressve atve flterng and 4 extra lnear bquad flterng. Those 8 atve dgtal flters are used for fttng of varous patterns of HL threshold urves. In ths paper a GB311 hp fttng program was developed for dgtal HAs n whh the most optmal DSP hp parameters were seleted from 4.7 bllon ombnatons of possble parameters.. DSP PARAMETER FITTING PROCEDURES AND RESULTS Fg. shows the ntal menu wndow of the present dgtal HA fttng program. The whole proedure of the parameter fttng s harted n Fg. 3. Fg. 1 Crut dagram of GB311(GB310) dgtal HA spef DSP hp [] Fg. The ntal menu wndow of the dgtal HA fttng Program.1 Audogram Hearng Threshold The frst step of the parameter fttng s to read the HL threshold of the hearng mpared person (Fg. 4).

2 ICCAS005 Selet Rght /Left, Memory M1M4 B-Quad Flter I/O Curve Audogram Read Audogram Choose Auto Fttng Algorthm Auto Fttng Set DSP Parameters Apply Fttng Formula (Fg6) Copy Parameters Volume Control & Feedbak Reduton Set Warnng Sound Set Dretvty June -5, KINTEX, Gyeongg-Do, Korea the relatve nrement of the amplfaton beomes smaller beause of nonlnearty. If any analog amplfaton hp an produe the smlar nonlnear frequeny response as the fgure for a partular hearng mpared person, the analog hp s spefally good enough for the person. However every hearng mpared person have eah dfferent amplfaton requrement, so that eah person has to have hs/her own spef analog hp. That s very uneonomal. Dgtal HA hps are desgned to adapt to suh dverse requrements B-Quad Flter Equalzer Dret Parameter Input Lower Threshold Low Level Gan Upper Threshold Hgh Level Gan AGCo Squelh Crossover Freq. Wdeband Gan Volume Control Ext. Volume Control Mute Noth Depth Noth Center Noth Wdth Tone Frequeny Tone Level Mem Tone Freq. Mem Tone Level HRX Low Battery Attak & Release Tme (Ch 14, AGCo, Squelh) Front Wave Mode Beta Low Freq Eq Mt M Atten Selet Programmer Kt GB311 Control Open, Whh Chp, Int Read Wrte Burn Fg. 3 The flow hart of the parameter fttng.. Fg. 5 HA amplfaton funton derved from the nonlnear FIG6 formula. Fg. 4 Ar onduton HL thresholds. x(left Ear), o(rght Ear).. Fttng Formula The seond step s to alulate the HA amplfaton as a funton of frequeny by a onventonal fttng formula suh as FIG6. Table 1 shows the nonlnear Fg6 Formula [1]. Table 1 Nonlnear FIG6 Formula [1]. IG Gan. HL Input. Input Level IG 40 db SPL 0 H < 0 db HL H -0 0 H 60 db HL 0.5 H +10 H >60 db HL 65 db SPL 0 H <0 db HL 0.6( H -0) 0 H 60 db HL 0.8 H -3 H >60 db HL 95 db SPL 0 H <40 db HL 0.1( H -40)1.4 H 40 db HL H Fg. 5 shows the amount of the HA amplfaton funton derved from the nonlnear FIG6 formula. The three ontnuous blak thn lnes of the fgure ndates how muh amplfaton should be done by the HA amplfer for three dfferent nput sound levels. As the nput sound level s bgger,.3 DSP hp parameters fttng The thrd step s to alulate DSP hp parameters for fttng to the HA amplfaton funton. The word, fttng, s sometmes onfused. In general fttng means fttng formula as n the seond step. The parameter fttng n the thrd step means the proper adjustment of the DSP hp parameters n order for the DSP hp to resemble to the HA amplfaton funton derved by the seond step. Fg. 6 shows the results of the fttng formula (three blak thn lnes) and the parameter fttng (three olored thk lnes) by a fttng program suppled by Gennum Co. The blue lne s for 40dB nput sound level, and the green and the volet lnes are for 60dB and 80dB nput sound levels respetvely. The parameter fttng seems to be all rght at low frequeny bands, but the parameter fttng s not well resemble to the HA amplfaton funtons at hgh frequeny bands. Therefore ths paper tred better parameter fttng than Gennum s. Fg. 6 The results of the fttng formula (thn lnes) and the parameter fttng (thk lnes) by a fttng program suppled by Gennum Co. Blue: 40dB Input Level, Green: 60dB Input Level, Volet: 80dB Input Level. If we look at the operatonal prnple of the Gennum 311

3 ICCAS005 DSP hp, some better optmal parameter fttng method ould be resulted. The Gennum 311 hp dvdes the frequeny band nto four hannels. Eah hannel boundary s defned as ross frequeny, CO, (Fg. 7). In Fg. 7 the red thk lne ndates a HA amplfaton funton. Eah hannel of Fg. 7 s ontrolled by eah dgtal flter; CH1Low Pass (LP) Flter, CHBand Pass (BP) Flter, CH3 Band Pass (BP) Flter, CH4 Hgh Pass (HP) Flter [5]. The four dgtal flter responses are summed to resemble to the HA amplfaton funton. June -5, KINTEX, Gyeongg-Do, Korea CF CF CF Fg. 7 Four hannels separately formed by four dgtal flters. The four dgtal flter responses are summed to resemble to the HA amplfaton funton. The hannel dgtal flter s Butterworth type. The frst hannel s omposed by the thrd order low pass flters, LP 3 1. f s ut-off frequeny and o 1 s rd f o the frst ross frequeny. The seond hannel s omposed by seond order hgh pass flters as well as thrd/fourth order low pass flters, ( HP nd LP4 ) ( 3 ) 1 th HP f o nd LP f o f o1 rd. f o The thrd hannel s omposed by thrd/ffth order hgh pass flters as well as seond/thrd order low pass flters, ( HP rd LPnd ) ( HP5th LP3rd ) 3 f o f o3 f o f o3. The fourth hannel s omposed by seond/ffth order hgh pass flters, ( HP ) ( ) nd HP. f o3 5th f o3 Table Butterworth dgtal flter formula. N s a number of order [5]. N th N -order Low-Pass Flter th N -order Hgh-Pass Flter Even N/ N/ s H( s) Hs ( ) k 1s + osφ ks+ k 1 s + os φk s+ ( N Odd 1)/ ( N H( s) s+ k 1 s + osφ ks+ 1)/ s s Hs () s+ s + os φs+ k 1 Gennum 311 hp has three ross frequeny parameters and eah CF parameter s algned wth 1619 fxed frequenes (Table 3). Also eah hannel has four parameters; LTH(Low Threshold), LLGAIN(Low Level Gan), UTH(Upper Threshold), HLGAIN(Hgh Level Gan) whh are used for nonlnear ompresson (Fg. 8, Table 4). Table 3 Gennum 311 hp s three ross frequenes algned wth 1619 fxed frequenes. [khz]. k Fg. 8 Nonlnear ompresson relatonshp between nput sound level and output sound level. LTH(Low Threshold), LLGAIN(Low Level Gan), UTH(Upper Threshold), HLGAIN(Hgh Level Gan). Table 4 Nonlnear ompresson fxed parameters [db] LTH n (n0 to 35) LTH 30 + n (n0 to 35) LTH n (n0 to 35) LTH n (n0 to 35) LLGAIN n (n0 to 30) LLGAIN n (n0 to 30) LLGAIN n (n0 to 30) LLGAIN n (n0 to 30) UTH n (n0 to 35) UTH 40 + n (n0 to 35) UTH n (n0 to 35) UTH n (n0 to 35) HLGAIN n (n0 to 30) HLGAIN n (n0 to 30) HLGAIN n (n0 to 30) HLGAIN n (n0 to 30) The ntal mnmum number of parameters for the parameter fttng are CF1(16), CF(19), CF3(17), LLGAIN1(31), LLGAIN(31), LLGAIN3(31), LLGAIN4(31) whh generate 4.7 bllon possble ombnatons of parameters (4.7 bllon 16x19x17x31x31x31x31). Those seven DSP hp parameters may be optmally alulated by mean square method whh mnmzes the dfferene between the desred HA amplfaton funton and the ampltude response urve derved by applyng dfferent parameter sets. The nput frequeny s a varable and we lmt the number of the nput frequeny for faster alulaton. Fg. 9 shows the results of the fttng formula (three blak thn lnes) and the parameter fttng (three olored thk lnes) by a fttng program developed by authors. In omparson wth Fg. 6 the optmal parameter fttng seems to be better at all frequeny bands than Gennum s

4 ICCAS005 June -5, KINTEX, Gyeongg-Do, Korea ( A >0. 0 ), Q s a qualty fator ( ). The oeffents of the dgtal bquad flter are lmted between and + beause of 15 bts sgned resoluton lmt. Therefore Aand Q should be adjusted to be wthn the lmt (a) Left Ear. Fg. 9 The results of the fttng formula (thn lnes) and the optmal parameter fttng (thk lnes) by a fttng program developed by authors. Blue: 40dB Input Level, Green: 60dB Input Level, Volet: 80dB Input Level..4 Compensaton for the mrophone and the reever The fourth step s to remove the resonane effets of the mrophone and the reever. Fg. 10 shows the frequeny responses of the mrophone and the reever respetvely. (a) EM4346 mrophone (b) ED3146SAT reever (Sonmrons Co.) Fg. 10 Frequeny responses of the mrophone and the reever. Dotted lnes are trunated responses. If the resonane effets of the mrophone and the reever are added to the optmal parameter fttng, the resultant response urves are shown n Fg. 11. The summed resonane effets of the mrophone and the reever result n the feedbak of the ITE type HAs. Therefore the Gennum 311 DSP hp has another four extra bquad dgtal flters for the ompensaton of the feedbak resonane effets (Fg. 1). Fg. 11 The results of the fttng formula (thn lnes) and the optmal parameter fttng (thk lnes) wth the resonane effets of the mrophone and the reever. Blue: 40dB Input Level, Green: 60dB Input Level, Volet: 80dB Input Level. Eah bquad dgtal flter s desgned by a seond order IIR (Infnte Impulse Response) dgtal flter as shown n Fg. 13 [6]. The oeffents of the dgtal bquad flter are dereved from the oeffents of the analog bquad flter ( H ( s) b ) ( s + b1s+ b0 / as + a1s+ a0) where s a enter/ut-off angular frequeny, A s an amplfaton rato Fg. 1 Four bquad dgtal flters are extra flters for the ompensaton of the feedbak resonane effets. (a) (b) H ( z ) b b 1 Z + b Z 1 + a 1 1 Z + a Z Fg. 13 The struture (a) and the formula (b) of the dgtal bquad flter. < b 0, b1, b, a1, a < +. Table 5 The oeffents of the analog bquad flter / H ( s) b s + b s + b a s + a s + a [6] Flter Type EQ flter (Parametr Equalzer) LP flter HP flter BP flter ( ) ( ) LF Shelf flter HF Shelf flter 1 0 Amplfaton b b 1 Rato A 1.0 A Q 0 <A < ( A ) Q 0 < A < A 0.0 A 0 < A 0.0 ( A ) Q 1.0 A 1.0 A 0 <A < A A A 0 <1.0 <A 1.0

5 ICCAS005 b 0 a a 1 a ( Q A) Q A 1.0 Q Q Q 1.0 A 1.0 A 1.0 / A June -5, KINTEX, Gyeongg-Do, Korea Fg. 14 The results of the fttng formula (thn lnes) and the optmal parameter fttng (thk lnes) wth the resonane effets anellaton of the mrophone and the reever by four bquad flters. Blue: 40dB Input Level, Green: 60dB Input Level, Volet: 80dB Input Level. 1 / A A / A The blnear transformaton from S doman to Z doman, ( ) ( H ( s) b s + b1s+ b0 as + a1s+ a0) H ( z) ( b ) ( 0z + b1z+ b z + a1z+ a), s done as flowng equatons; b0 4 b + b1 + b0 4 a + a1 + a0 b1 b0 8 b 4 a + a1 + a0 b 4 b b1 + b0 4 a + a1 + a0 a 1 a 0 8 a 4 a + a 1 + a 0 a 4 a a 1 + a 0 4 a + a 1 + a 0 where T (( π f ) f ) ( π f ) (Equaton 1) (Equaton ) (Equaton 3) (Equaton 4) (Equaton 5) tan s, f s 300 [Hz] Fg. 14 shows the results of the optmal parameter fttng wth the resonane effets anellaton of the mrophone and the reever by four extra bquad flters. In omparson wth Fg. 11, Fg. 14 shows more prese fttng to the fttng formula urves than Fg. 11. Fg. 15 shows the nonlnear nput-to-output ompresson urves for four dfferent frequenes. And Fg. 16 shows nonlnear output sound pressure levels aganst nput sound pressure levels as funtons of frequeny. Fg. 15 Nonlnear nput/output ompresson urves for four dfferent frequenes. Fg. 16 Nonlnear output sound pressure levels (db SPL) aganst nput sound pressure levels as funtons of frequeny..5 Compensaton for the ear anal resonane The ffth step s to ompensate the nserton loss of the ear anal resonane effet. When an ITE HA s nserted nsde an ear anal, the ear anal s bloked wth the ITE HA. Then the nserton loss of the ear anal resonane effet happens. Therefore a dgtal HA should onsder the ompensaton of the nserton loss. The man frequeny band of the anal resonane s 14 khz. For ths reason the audogram may be modfed as shown n Fg. 17. (a)

6 ICCAS005 Fg. 17 Audograms (a) wthout and (b) wth the ompensaton of the nserton loss. x(left Ear), o(rght Ear). Fg. 18 (b) shows the results of the optmal parameter fttng wth the resonane effets anellaton of the mrophone and the reever by four extra bquad flters as well as wth the ompensaton of the left ear anal resonane effet. June -5, KINTEX, Gyeongg-Do, Korea Fg. 19 The results of the fttng formula (thn lnes) and the optmal parameter fttng (thk lnes) wth the resonane effets anellaton of the mrophone and the reever by four bquad flters as well as wth the ompensaton of the rght ear anal resonane effet. Blue: 40dB Input Level, Green: 60dB Input Level, Volet: 80dB Input Level. 3. CONCLUSION Left Ear (a) wthout ear anal ompensaton Ths paper apples a spef DSP hp suh as Gennum GB311 to dgtal ITE type HA fabraton and shows the result of the optmal parameter fttng program development for the hp. Detals of hp parameters are explaned. The fttng program has ompleted features from audogram nput to DSP hp nterfae. The ompensaton effets of the mrophone and the reever are also nluded. The omparson between Fg. 6 and Fg. 9 shows that the DSP hp parameters suh as 4.7 bllon possble ombnatons of parameters should be optmally hosen to resemble to the amount of hearng threshold ompensaton derved by the fttng formula. Extra dgtal flters need to be added for the omplete fttng to the HA amplfaton funton. Even though the present DSP hp parameter fttng program provdes the best fttng for the fttng formula, the fnal prese fttng should be manually adjusted by the user, that s, the hearng mpared person [7,8]. ACKNOWLEDGMENT Ths study was supported by researh fund from the mnstry of ommere, ndustry and energy (MOCIE Korea) standardzaton tehnology development projet(standardzaton study on dgtal hearng ad: projet number ) n 004. (b) wth ear anal ompensaton Fg. 18 The results of the fttng formula (thn lnes) and the optmal parameter fttng (thk lnes) wth the resonane effets anellaton of the mrophone and the reever by four bquad flters as well as wth the ompensaton of the left ear anal resonane effet. Blue: 40dB Input Level, Green: 60dB Input Level, Volet: 80dB Input Level. And Fg. 19 (b) shows the results of the optmal parameter fttng wth the resonane effets anellaton of the mrophone and the reever by four extra bquad flters as well as wth the ompensaton of the rght ear anal resonane effet. REFERENCES [1] Harvey Dllon, "Hearng Ads", Prnted by Theme, 001. [] m [3] [4] y.html [5] Chaewook Lee, Reent dgtal sgnal proessng, publshed by BooksHll Co., 00. [6] Gennum Co., Bquad flters n PARAGON dgtal hybrd, Do. No , 001. [7] B. Kollmeer and V. Hohmann, "Loudness estmaton and ompensaton employng a ategoral sale," n Advanes n Hearng Researh, G. A. Manley, G. M. Klump, C. Köppl, H. Fastl, and H. Oeknghaus, Eds. Sngapore: World Sentf, pp [8] S. Launer and B. C. J. Moore, "Use of a loudness model for hearng ad fttng. V. On-lne gan ontrol n a dgtal hearng ad," Int. J. Audol., vol. 4, pp. 6-73, 003. (b) wth ear anal ompensaton