uson wrote:
Other than buying a preamp with such a switch, it would seem a
relatively easy device to design. Needs to be completely inaudible, and
avoid switching "pops".

The actual device need be nothing more complex than a double-pole,
double-throw switch for each channel.

However, your desire for it to be "completely inaudible and
avoid[ing] switch pops" is an impossibility. Only if you switch
during absolute silnce is this possible. At any point where there
is signal voltage, no matter HOW you do it, there MUST be an
abrupt change in the signal, and and the result WILL be a
switching transient of some level. The degree of audibility is
dependent, of course, on the instantaneous signal at the moment
of the switch and the spectral density of the music. It'd be harder
to hear it on thrash metal than it would on a recorder solo, for
example, because any switching transient is going to cause a
fairly wide-band, spectrally dense signal, and already having a
lot of energy throughout the spectrum is likely to mask it.

It's certainly possible, given sufficient sophistication, to build
a curcuit with soft switching: instead of the transition happening
at a specific instant, it's xpread out over a few milliseconds with
a "fade" between the two states: that'll reduce substantially the
potential audible impact of switching but has some costs, the
major one being that, technically, it's far more complicated than
a simple switch. There are, undoubtedly, also those that might
argue that such sophistication MUST have deleterious audio
impact, though, as an a priori argument, this is simply speculation.


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