Peculiar Ground Problem

Hi

I have a DSP Board which does some audio post synthesis interfaced though I2S (input and output). When I use pass-through or bypass, I can head the audio at the output stage. When I remove bypass and pass it though synthesis stage, I can see audio signals on the output (after processing) but I am unable to hear audio. I can hear the audio when I provide a kind of antenna/ground through body on some places on board (Supply, GND, connectors, etc). Since DSP board has only digital gnd, I am connected to the power supply and ground of output stage only.

Thanks Avinash