I have an ADUA1761 audio codec eval board I'm using for product development. The current setup is simple and is as follows:
1) Rotary encoder attached to GPIO pins 0 and 1, configured using a RotVol1 processing block in SigmaDSP. Works well.
2) Analog output stage implementing differential to single-ended conversion and a ~100kHz low-pass multi-feedback filter. No issues in standalone tests.
3) Input taken from L/R AUX inputs, routed to ADCs, through DSP core and then to L and R differential outputs respectively.
4) All unused inputs/outputs/devices are muted. All volume controls in the CODEC signal path are set to 0dB.
The problem symptoms are straightforward; when playing back signal from a line level source, there are a large number of very loud pops and clicks. These seem to correlate to signal peaks from the source and seems to indicate some sort of clipping. This occurs even when the rotary volume control is set to minimum (taper table value of 0). Altering the ADC and DAC volume control settings in the digital setup menu, does not seem to affect the problem whatsoever. The pops/clicks seem to be much more pronounced when the rotary volume control is set at lower levels but is present throughout the volume taper. The problem does NOT seem to occur when using a lower level input device, i.e. an MP3 player.
Any information as to the cause for this problem and a possible avenue to solve it would be greatly appreciated.