GA3222 Preliminary Data Sheet

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February 2006

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7.3.3 Time Constants

The preconfigured attack and release times are 200ms and 20ms respectively for

two main reasons:

1. To ensure that the noise reduction system is not activated during softer

phonemes in speech (slower expansion attack time) and that the system

quickly responds to the onset of speech (faster expansion release time). The

typical duration of phonemic gaps between syllables in speech is about

150ms, so the expansion attack time should be longer than this to avoid

distorting the speech envelope.

2. Slow time constants are in keeping with ADRO processing and are optimized

to preserve the sound quality of speech.

7.4 Adaptive Feedback Canceller

Advanta’s feedback canceller reduces acoustic feedback by forming an estimate

of the hearing aid feedback signal and then subtracting this estimate from the

hearing aid input. Therefore, the forward path of the hearing aid is not affected.

Unlike adaptive notch filter approaches, Advanta’s feedback canceller does not

reduce the hearing aid’s gain.

Figure 7-1: Adaptive Feedback Canceller block diagram

G

Σ

H'

H

+

-

Feedback path

Estimated feedback