Circuit for improvement of noise immunity of audio signal

摘要

The range of audible frequencies is divided among a number of channels, in each of which the signal level is measured (34) and compared (31) with a specific limit for the channel. A binary output (29) is applied to a gain control circuit (26) for the amplifier (24), of the digitised and delayed (21) audio signal. When the audio level falls below a threshold for a fixed length of time, the gain is reduced gradually to a minimum. Conversely the gain is restored progressively to a maximum value when the useful signal reverts to a level above the threshold.