I connected a microphone to input 1 of the ADAU1761 EVB in single-ended mode, then I attached an amplified speaker to the stereo output, setting the speaker volume to max.
Starting from a working output configuration, in which all the mixers in the signal path are on and I can hear my voice amplified from the speaker, I muted the record signal path, i.e. mixer 1. If I blow in the mic, or I attach a function generator in place of the microphone, I can still hear sound from the speaker.
Muting the output or changing the configuration is not helping. The signal is, by the way, going to all the outputs, not only those I was using before muting.
Strangely, this goes away if I keep mixer 1 unmuted, and I mute the output using LOUTM or ROUTM (register 0x4025).
I hoped to have found a workaround using that trick, when I tried my current configuration, which is using the input in differential mode. With that setup, I can't find a way of completely shutting down the input->output path.
This is a big problem for my application, since one of the outputs of the ADAU is captured by another board, and there is a loop which gives an echo if I can't mute it.