Flexibility in Frequency Response Shaping and Signal Processing With Analog Hearing Aids

¹ Argosy Electronics, Eden Prairie, MN

Mainly because of packaging size limitations, most amplifiers for in-the-ear (ITE) and in-the-canal (ITC) hearing aids have performed linear processing and had a class A output stage. Recent advances in the miniaturization of analog semiconductor technology have made it possible to package much more sophisticated signal processing circuitry and push-pull and class D output stages in ITE and ITC hearing aids.

These advancements have been used in hearing aids to improve sound quality, enhance the speech signal to emphasize weak consonants, provide increased flexibility in frequency response shaping, and reduce the amplification of undesired noise. Although digital programmability offers increased flexibility in hearing aid fittings, in most programmable hearing aid designs it is the analog portion of the circuit rather than the digital portion that performs the signal processing functions.

Although "true" digital signal processing holds promise for further dramatic improvements in hearing aid performance, the capabilities of analog electronics are just beginning to be exploited. Through advances in low-voltage CMOS circuitry, analog ITE and even ITC hearing aids are now being made with multiband amplifiers that have relatively steep filter slopes.

These small, nonprogrammable hearing instruments are essentially master hearing aids for frequency response shaping that require only a few potentiometers and an ordinary screw-driver for adjustment. Consequently, analog circuitry should not be totally abandoned as yet in favor of digital circuitry.

Key Words: headroom, noise reduction, multiband, consonant-vowel ratio, saturation

Submitted on February 18, 1993
Accepted on March 18, 1993