Audio setbacks

Well, I knew I didn't have all of the audio issues worked out, but I didn't know it was this bad.

I finally broke out one of the DS1807 digital pots and got it working.   Some notes:
* I think I have the audio biased around +2.5v correctly.  Even without this the pot works and I don't hear clipping, but it's noticeably better with.  I'm probably still screwing something up here.   No mater what, the audio board layout I've got is definitely wrong and needs a pretty big re-work.
* The zero-point crossing feature of this chip is not working.  I've tried tying AREF to +2.5 as well as to the other end of the wheatstone bridge, but there is still a *click* when level changes.
* My row/column scanning pauses *very* noticeably when writing over the I2C bus.  this means the write is taking a really long time, like 0.5sec.  I should dig into the Arduino Wire library and see what I find;  perhaps I'll need to resort to port manipulation.   I'd rather not :(
* Lighting any LEDs in the matrix causes noise.  Lighting many LEDs causes a LARGE amount of noise.  It seems to go away when I turn the pots all the way down, meaning it's not noise related to the ATMega328 crunching or the shift registers doing their thing...   This is probably good news, as I'll have the LEDs pretty well isolated in the final product.
* Writing over I2C is LOUD.  A half-second of BZZZZT happens on every write.  I am sure there are ways to avoid this, as the DS1807 is primarily intended for audio applications.  I've just gotta get better at isolation and grounding.
* USB noise is still present, especially when I do something graphically heavy on the computer.  I'm encouraged because it was much, much worse before.  I'm assuming this is because components are in different locations on the breadboard now, and that means it's probably fixable with intelligent layout.

In my last post I defined my main issues to be:  snappy display and responsive controls.  I'm adding noise-free operation to this list.