Volume control intermittent crackling

Why not placing the volume control after the filter ?

I guess another solution would be to use a volume control with Slew

Hello zdr,

I think the problem is that all ADCs have a DC offset. Many of them have a built in high pass filter but the ADC in the ADAU1701 does not. So you need to add a DC block to block out this DC. It can be significant and when you EQ up the low frequency, like with a subwoofer, you also amplify the DC level as well.

So put these in and I expect you will see a big difference.

The cutoff frequency is really low so it will not affect your low end.

Also, I agree with GLeclerc, You really HAVE to use a volume control with slew for any volume control that will be used in real time as a volume control. If it is just a calibration then it will not be changed during regular operation you would not have to have a slew type. But a regular volume control will have zipper noise and the slew will solve that. Your description of the crackling sounds like it could be the zipper noise.

Dave T

I'm afraid it did not make a difference. I still hear a loud pop intermittently while moving a slider. I also have a DC blocking film caps at the ADC inputs, so there should be no DC in there.

Hello zdr,

The DC can come from the input, agreed, but the DC I am talking about is generated by mismatches inside the ADC so external capacitors have ZERO effect. You MUST add the DC block filter in the SigmaStudio schematic.

Then make sure you are using a slewed type of volume control and make sure the writes to the part are Safeload writes.

I have seen a few places where SigmaStudio does not use safeload writes when it should. See what comes up on the Cpature window when you adjust the control.

Dave T