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Volume control dependent noise in ADAU1701

Question asked by Tipo1000 on Sep 6, 2011
Latest reply on Sep 6, 2011 by BrettG

Hello,

 

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?

 

Thanks,

Timo

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