Volume Tracking of one Stereo Signal by Another

You're correct that you cannot do this because the ADAU1761 has two discrete ADC channels. In order to do what you want to do and mix the signals in the DSP core, you would need to be able to input each of the four channels (I assume you're talking about stereo signals) discretely to the DSP. Both the mic and aux inputs can be input to the core; see Figure 32 in the ADAU1761 datasheet for a diagram of the input mixing options.

You could control the gain of the signals in the DSP if you use an additional ADC to extend the analog input capabilities of the system. Connecting a codec like an ADAU1361 to the ADAU1761's serial input port will give you four input channels that can be processed separately in the DSP.

Thanks Jerad, that's a good idea. The ADAU1361 seems almost as complicated as the 1761 though. I suppose another option would be to use two 1761 and run the left and right of each source separately through it's own DSP: so left mic tracks left line in one chip and right mic tracks right line in the other. Hmm, I was trying to keep the cost and component count down. More thinking to do...

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Thank you,
EZ Admin