Distorted Audio
An experimental hearing aid was constructed (courtesy of Mead Killion, Russ Tomas, Norm Matzen, Mark Schmidt, and Steve Aiken) where the peak input limiting level could be adjusted. The peak input limiting level is also colloquially known as the "front end" of hearing aids. This is the maximum level that can be provided to the analog-to-digital (A/D) converter in modern hearing aids. Most modern digital hearing aids cannot handle inputs in excess of 96 dB SPL. If so, distortion will occur and no amount of software reprogramming (that occurs later in the processing route) will improve things.

In these files, all other hearing aid parameters such as gain, output, compression settings, and frequency response, have been kept the same. The only change is in the level of the peak input limiting level.

All files have the same presentation format: Peak input limiting level of 115 dB SPL, 105 dB SPL, 96 dB SPL, 92 dB SPL, and 115 dB SPL again.

File 1 is for speech at 60 dB SPL input. Note that there is no real effect of peak input limiting level setting on the speech clarity since speech is a relatively quiet signal.

Files 2 and 3 are for music at 90 dB SPL and 100 dB SPL input levels respectively. With the normal playing and listening levels of music that are evident in our society, peak input limiting levels that are too low will cause an unresolvable distortion.

File 1: Combination 60 dB SPL
File 2: Combination 90 dB SPL
File 3: Combination 100 dB SPL

For more information go to www.MusiciansClinics.com/articles.

Marshall Chasin, AuD,
Doctor of Audiology
Director of Auditory Research
Musicians' Clinics of Canada