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On Thu, 27 Oct 2011 17:59:59 GMT, (Don Pearce) wrote:

On Thu, 27 Oct 2011 09:11:17 -0700, DaveC wrote:

Or, as is not uncommonly done these days in portable digital players,
establish a floating ground for the purpose of providing and signal for the
(floating) load, so that the difference between the output and the floating
ground can become negative.

Which raises the question I was pondering recently: is it OK to connect 2
computers' sound cards' grounds together?

No. You will certainly create a ground loop which will result in mains
hum.

This is certainly likely but not a foregone conclusion. In any case, it's
"OK" (i.e. not dangerous). As long as the computers are plugged into the same
circuit, it's quite possible that he can get away with it, assuming line
levels. If hum is a problem, coupling capacitors or cheap audio transformers
will usually solve it.