Our application has 8 steps x 4dB ( =32dB) volume control in FW. It ranges so that max volume gives +12dB gain from input to output and min volume attenuates -20dB. 18k ADC resistor is used giving 2VRMS full range.
See the attached pic for noise levels for 9 volume positions. First steps increase noise 0.5-1dB and gradually moves to +4dB more noise per step. This was measured the ADC input grounded. Measuring with mini board gave similar results so the problem seems not to be in our HW.
Is it even feasible to have this kind of volume control in FW? Or what is wrong?