"fredbloggstwo"
wrote in message

So my question is this: is there any evidence that the
layout of pcbs does affect audio quality?

Depends, but often there is.

IME power amps are the trickiest, as are regulated power supplies. It's
about high currents. One of the worst power supply designs I've ever found
was in a Heath THD analyzer. I knocked the out-of-the box residual down by
about 1/3 just by changing how the filter cap land patterns were laid out. A
strategically placed piece of 14 guage copper wire in one place, and a cut
land pattern someplace else, if memory serves.

People talk about star grounding, but IME stars vary, depending on what the
points connect to, and how.

Mixed signal circuits (e.g. DACs and ADCs) can be very sensitive to layout.

If so why?

In audio circuits, it seems like grounding can be the big issue. Of course
at very high RF frequencies, things get very tricky.

I've experiments with various grounding schemes while the circuit was
amplifying say a 20 KHz sine wave, with the output of the amp hooked to an
analyzer. The differences often show up as spiky distortion residuals.

The type of evidence is things like the use of rounded instead of
right-angle corners. (For example, if I
remember my EM theory correctly, sharp points are the
most effective for radiating an electric field so could
right angles could radiate and produce cross-talk)

That's RF, for you. Probably more of an issue with mixed signal circuits,
because of the clocks and other digital lines.