As tman mentioned, you're looking at the wrong device.

Thanks, to both of you, that pushed me in the right direction. I have the recording channel set to the microphone input now.

What isn't clear to me (I haven't really looked) is how to ensure that the microphone input is played.

I don't want to play back the recorded mic input.

The CS4231a has a limited sampling rate of 22.05KHz.

Hmm, actually I'd like to record at 16KHz. I've tried setting the samplerate using EMPEG_AUDIOIN_WRITE_SAMPLERATE as definded in empeg.h. It works when I set it to 22050, which it is already set to anyway, but fails for 16000. Is the CS4231a's samplerate locked as well?