CM6500B Datasheet, PDF (19/36 Pages) C-Media Electronics – USB Audio Sound Chip

CM6500 / CM6500B
USB Audio Sound Chip
7 Function Description
7.1 Recording AGC
Automatic Gain Control (AGC) is an automatically controlled method to adjust with intensity of signal;
AGC is closes the return circuit; that is by the negative response system too.
AGC is by way of compressing volume, Will increase Gain first when AGC is started, Set up the upper and lower
limits of the signal; compress the dynamic range of sound. Usually use the occasion of AGC, should be recording
and producing and speaking sound, or volume is being changed under little environment. If the lasting low voice
of volume, AGC will enlarge volume, volume is sustained loudly, AGC will reduce volume.
FEATURES
Programmable AGC Parameters
Selectable Gain from –12 dB to 45 dB in 1-dB Steps
Selectable Attack, Release and Hold Times
AGC Enable/Disable Function
Limiter Enable/Disable Function
Pre-Detect Limiter Level Function
Two-Channel AGC Independent
Under input source types, to set AGC gain max/min limit
I2S rec
Digmic
Analog mic
+12~ -16DB
+20 ~ -16DB
+30 ~ 0DB
0xf9= 0x1c (max)+fix gain(9db) = 0x25
0cfA= 0x00(min)
0xf9= 0x24 (max)+fix gain(9db) =0x2d
0xfA= 0x00(min)
0xf9=0x0F+fix gain(9db) inv -> 0x39(max)
0xfA=0x2D
inv -> 0x12(min)
AGC Variable Description
Fixed Gain: The normal gain of the device when the AGC is inactive.
Limiter Level: The value that sets the maximum allowed output amplitude.
Attack Time: The minimum time between two gain decrements.
Release Time: The minimum time between two gain increments.
Hold Time: The time it takes for the very first gain increment after the input signal amplitude decreases.
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