I’ve got the Lexicon Alpha hooked up to one of the USB ports on my MacBook. I am running a boom box tape deck out the headphone jack (1/8") to a 1/4" adapter into the Line 1 input into the back of the Lexicon. I have audio out going to a set of computer speakers.
I am only getting the left channel to pick up on the Audacity software, though. When I listen with headphones to the tape player and the Lexicon, I get stereo, but I’m not getting it on the monitor or recording.
The Alpha is not a mixer. Whatever you plug into the XLR on the back will appear on the Right in your stereo show. The instrument connection on the front appears on the Left in your show, whether it started out stereo or not.
The stereo monitoring switch just feeds those single sound channels to both headphones. That’s just for overdubbing convenience. You still can’t cross-mix the XLR and the Instrument in the show.
It’s possible GarageBand is spreading “Left Tape” across left and right show.
I think I can force Audacity to do that with a Behringer UCA202 stereo USB adapter. I can apply a full stereo show to the UCA202 and two channels will make it to Audacity, but it’s really two copies of “Left,” not full stereo Left and Right. Right sound dies a quiet death inside the adapter.