An ADAU1761 based product is entering pre-production. The product designers have highlighted an area of concern. They'd like to understand what they are hearing. To hear:
Load the attached project to the ADAU1761 evaluation board. Turn the volume slider to full. For the LINP/LINN pair: Toggle Mixer enable to "enabled". Toggle Differential path to "disable". "Mute" left volume control. By toggling these two: Mixer Enable and Differential Path, with no audio inputs, we can hear modem like sounds. They are very apparant using a decent set of headphones. Once the sounds appear they will continue for Mixer Enable "enabled", Left Vol Control "Mute" and Differential Path "Disable" settings. There are other conditions that produce the modem lke sounds as well and can be found with a little experimentation.
The customer would like to know where these are coming from and what if anything can be done about it.