Introduction The analog-to-digital converter （ADC） channel for the AIC3254 provides an AGC function for recording. AGC can be used to maintain a nominally-constant output level while recording. All the ADC processing blocks （also known as PRBs） support this AGC functionality. The AGC architecture supported in the PRBs provides independent control of the AGC function for the left and right channels. For example， if the target AGC gain is –12 dB， the left channel signal level is –14 dB， and the right channel signal level is –18 dB， the AGC will then bring both channel signals to –12 dB. The gain applied to the left channel would be +2 dB while the gain applied to the right channel is +6 dB.

　　In some applications， however， it is desirable to maintain the level difference between the left and right channels while using AGC. This capability is also known as stereo AGC functionality. In stereo AGC， the same gain is applied to both the left and right channels. In the above example， then， for stereo AGC functionality， +2 dB will be applied to both channels. The left channel will move up to –12 dB， and the right channel will move up to –16 dB. The relative level difference of 4 dB is maintained between the left and the right channels.

　　Figure 1 shows the difference between normal AGC and stereo AGC operation.