The iriver audio amplifier chip (UDA1380 iirc) is resposible for the amplification of outgoing and incoming audio.
It has an analog amplification stage and (for the incoming audio) a digital one.
The digital amplification is done on the internal digital signal, which is 20 bits (it is later converted to 16 before handing it over to rockbox)
Incoming audio amplification has following steps (of the top of my bad memory):
- analog: 2dB
- digital: 0.5dB
Rockbox uses the digital steps inbetween the analog ones to give a smooth gain. The usage of digital gain is restricted to the minimum.
AGC-SAFETY will lower the gain when clipping is at risk (-2dB I think), just like you would. It has a configurable speed, meaning the time it needs to see clipping before lowering gain. That allows you to ignore the occasional whistle, shout, clap... but of course makes it slower to respond to real clipping.