A sound card can't be shared between two computers.
You probably don't need a
sound card for what you are trying to do at all, unless your software doesn't work well
with Apple's built-in audio.
You just need to adjust the level, balance and
possibly mix the headphone stereo output to mono and feed it into a normal microphone
The built-in audio quality on most modern macs is quite good and I've
never encountered a noise problem if proper isolation transformers are used.
If I need stereo, I sometimes just use a regular dual instrument DI (or two mono ones)
because there are always DIs around.
Connect the Macintosh to the instrument
inputs of the DIs with a Y cable that has a TS plug for each channel on one end and a
3.5mm trs cable on the other. These are standard cables, easily available. If you just
can't find one, try a 3.5mm stereo to rca cable of the sort used to connect ipods to hifi
systems with a pair of RCA to TS adapters.
If Mono is good enough, you can
use just one DI and leave the other dangling. You can get mono output from the Macintosh
by setting the "System Preferences / Accessibility / Play Stereo Audio as Mono "option
which will mix the two channels and send them to both right and left outputs at the same
Don't be tempted to just use a Y cable to connect the outputs together
this will cause distortion or even damage the output device (although a "passive mixer
cable" with isolating resistors can be used if you have one).
Of course if
the computers are close to the mixer you can skip the DI and XLR cabling and just plug the
TS connectors right into line inputs on your mixer.
If you do need
XLRs, The most convenient solution is something like this:
mixes the left and right channels down to mono and sends them through a transformer to an
XLR after allowing you to adjust the level with a handy knob.
I regularly use
the Rapco devices to connect various things including MacBooks on stage here in the US
because they are a complete solution and easily available, but similar things are made by
many suppliers in both mono and stereo versions. Mono is usually a better choice than
stereo for this kind of thing and it only ties up one XLR input.
isolated, the Macbook's audio is quite flat and clean with low distortion. It has a very
gradual and very slight roll-off below 100hz and above 15khz - but that's usually what you
hope this helps,
Edited by mpvano (27/11/12 06:14 AM)