Automatic gain control

The purpose of an automatic gain control (AGC) is to self-adjust the front-end gain of the LPC analyzer in such a way that the speech waveform is more accurately quantized by the analog-to-digital converter. Tests in the past have indicated that properly amplified speech produces higher intelligibility scores at the narrowband LPC output because both filter and excitation parameters are more accurately estimated. In addition, properly amplified input speech results in properly amplified speech at the receiver, which is highly desirable for listening in a noisy environment.