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. 1996 Mar;1(1):5-39.
doi: 10.1177/108471389600100102.

Theoretical and practical considerations in compression hearing AIDS

F K Kuk  1
Affiliations

Theoretical and practical considerations in compression hearing AIDS

F K Kuk. Trends Amplif. 1996 Mar.
No abstract available

PubMed Disclaimer

Figures

Figure 1.
Figure 1.
Representation of soft, conversational and loud speech into the auditory dynamic range (A) normal hearing, (B) sensorineural hearing loss.
Figure 2.
Figure 2.
Example to show how linear amplification without limiting (25 dB gain), when applied to soft, conversational and loud speech, may alter its representation in the residual auditory dynamic range of a hearing-impaired ear.
Figure 3.
Figure 3.
Example to show how linear amplification with peak clipping (25 dB gain), when applied to soft, conversational, and loud speech, may affect its representation in the residual auditory dynamic range of a hearing-impaired ear.
Figure 4.
Figure 4.
Frequency response curves of a hearing aid with linear amplification when tested with composite noise at (A) 65 dB SPL, and (B) 85 dB SPL (hearing aid in saturation).
Figure 5.
Figure 5.
Hypothetical loudness growth functions for a normal hearing listener and hearing-impaired listener.
Figure 6.
Figure 6.
Three approaches to “compress” the entire speech range into the residual auditory dynamic range of the hearing-impaired ear: (A) compression limiting (CL), (B) wide dynamic range compression (WDRC), and (C) automatic volume control (AVC).
Figure 7.
Figure 7.
Input-output (I-O) curves of different hearing aids. (A) Linear with peak clipping, (B) wide dynamic range compression, and (C) compression limiting.
Figure 8.
Figure 8.
Input-gain curves of the hearing aids shown in Figure 7: (A) Linear with peak clipping, (B) wide dynamic range compression, and (C) compression limiting.
Figure 9.
Figure 9.
Input-output curve showing the different static compression characteristics.
Figure 10.
Figure 10.
Schematic diagram of a compression circuit.
Figure 11.
Figure 11.
Illustration of attack and release times and associated output waveform from a compression hearing aid: (A) unamplified signal (B) linearly amplified output, and (C) compressed output.
Figure 12.
Figure 12.
Effect of long and short release times on the output waveform when the input has (A) short intra-syllabic interval, and (B) long inter-syllabic interval. “V” represents vowel and “C” stands for consonant.
Figure 13.
Figure 13.
Example to illustrate the reduction in compression ratio from the interaction between release time and inter-syllabic interval. (A) Unamplified signal, (B) linearly amplified signal, (C) short release time, and (D) long release time.
Figure 14.
Figure 14.
Effective compression ratio of a commercially available compression circuit with fixed release time of 50 ms, and adaptive release time.
Figure 15.
Figure 15.
(A) Hypothetical loudness growth function of normal hearing ear and moderately hearing-impaired ear. (B) Output intensity levels for normal hearing and hearing-impaired ears to reach the same loudness perception. The SPL difference between the normal and impaired ears represent the desired gain in the hearing aid to achieve “normal” loudness for the impaired ear.
Figure 16.
Figure 16.
Hypothetical audiogram showing the difference in dynamic range (and thus compression) characteristics across frequencies.
Figure 17.
Figure 17.
Amount of gain (shown by the length of the arrows) provided by a WDRC (←) and a CL (￩) circuit as illustrated on a loudness growth function.
Figure 18.
Figure 18.
Illustration of how compression can affect the temporal intensity relationship among acoustic segments. (A) No amplification, (B) linear amplification, (C) compression with short release time, and (D) compression with long release time.
Figure 19.
Figure 19.
Placement of volume control in a compression circuit: (A) AGC-O, and (B) AGC-I.
Figure 20.
Figure 20.
Effect of volume control rotation on the input-output function of an (A) AGC-O hearing aid, and (B) AGC-I hearing aid.
Figure 21.
Figure 21.
Effect of volume control rotation on the output of an AGC-O hearing aid: Increasing VC leads to an increase in output despite reducing the compression threshold except where saturation is reached.
Figure 22.
Figure 22.
Effect of volume control rotation on the available headroom (HR) in an (A) AGC-O and (B) AGC-I hearing aid.
Figure 23.
Figure 23.
Effect of volume control rotation on the absolute output intensity range in an (A) AGC-O and (B) AGC-I hearing aid. The symbols represent the output level for specific input and VC setting. “O” represents an input from 60 dB SPL to 70 dB SPL and VC = 3. “□” represents an input from 70 dB SPL to 80 dB SPL and VC = 3. “X” represents an input from 70 dB SPL to 80 dB SPL when the volume is turned down to VC = 2.
Figure 24.
Figure 24.
Effect of VC rotation on the long term signal-to-noise ratio. (A) Signal (S) and noise (N) not sufficient to reach the compression threshold. The SNR at the input is preserved. (B) Reduction in output SNR at higher input level. (C) SNR is maintained at a reduced value in an AGC-I hearing aid when the VC is lowered, and (D) SNR at the input is restored in an AGC-O hearing aid with VC reduction.
Figure 25.
Figure 25.
Possible placement of filter within a compression hearing aid: (A) pre-filter, (B) post-filter, and (C) loop filter. “F” represents the filter.
Figure 26.
Figure 26.
(A) Frequency response of the filter and (B) I-O curve of the compression circuit used in the illustration.
Figure 27.
Figure 27.
Effect of filter position on compression threshold: (A) pre-filter, (B) post-filter, and (C) loop-filter.
Figure 28.
Figure 28.
Effect of filter position on input-output curve: (A) pre-filter, (B) post-filter, and (C) loop-filter.
Figure 29.
Figure 29.
Effect of filter position on frequency response curve at 300 Hz, 1000 Hz, and 3000 Hz: (A) pre-filter, (B) post-filter, and (C) loop-filter. The input levels are indicated as parameter.
Figure 30.
Figure 30.
Effect of filter position on frequency-gain curve at 300 Hz, 1000 Hz, and 3000 Hz: (A) pre-filter, (B) post-filter, and (C) loop-filter. The input levels are indicated as parameter.
Figure 31.
Figure 31.
Schematic illustration between a (A) single-channel compression hearing aid, and (B) three-channel compression hearing aid.
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References

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