I am using 4 MCP4261 dual channel 100k digital pots to control the volume of 8 audio signals coming out of 8 Somo 14-d players and going into a philips TDA1516BQ amplifier. The pots are controlled using the Mcp4261 library by dreamcat4 http://arduino.cc/playground/Code/Mcp4261.
The system takes 8 analogue readings from resistance rubber cords (as you pull them, their resistance increases) and maps that out to a value useful for the MCP4261 chips, then sends that value out to all 8 pots bye way of 4 mcp4261 instances, using SPI. Originally I had it set up to control the Somo audio players using the serial volume control command they have, but there was far too much noise and the serial frequency was 5kHz, which is well within audible range.
I went for the digital pot option and generally they are good, but there seems to be a clicking issue when they have to move fast. If they are moved slowly, the audio signal is nice and cean, but the faster they are changed, the louder the clicks get. I have generally minimized this by only sending when the value has changed, and keeping the polling as quick as possible, so that the digital pots are updated quickly enough to allow for a smooth transistion, but I can't seem to fully eradicate the clicks.
Does anyone have an idea how to make this transition sound smoother? I have tried putting capacitors accross the audio in and out at the pot and between the out and ground. If I put a 100nF cap on either, the clicks go, but so does a good range on the signal. The bass is lost and the linearity of the pot gets messed up. I've tried lower value capacitors, which decrease the damaged to the audio signal, but the clicks are louder.