I am implementing a new design using the ADAU1761 and currently have a couple of performance issues that I need to resolve. Both of the issues below are present on the development board ADAU1X61EBZ and my own hardware.
1. The audio from the ADC (line input) has a low level (~-80dBFS) spurious 'birdy' that varies in frequency with time but usually settles around 5.5KHz. It's frequency can be changed / modulated by touching a scope probe on the line input pin of the 1761. I have been unable to supress this spurious response.
The spurious 'birdy' is only present when the line input is connected to the ADC in the mixer config.
2. What is the isolation between the analog inputs and the analog outputs? I can't see this specified on the datasheet anywhere. To test this I am driving the line input with 1VRMS sinewave at 1KHz, and measuring the output with the input mixer paths disabled. A far as I can tell the isolation is less than 50dB which seems rather poor.
Any help greatly appreciated.