If you record the output from Skype, unfortunately you only get their end of the conversation, because the audio signal does not include the input from your microphone.
It is straightforward to use Soundflower to combine signals from multiple inputs into a recording that includes both sides of the conversation. I started playing around with doing this in GarageBand’s podcast studio.
What is decidedly not straightforward is separating the two sides of the conversation into separate tracks, so they can be mixed after the fact. I finally figured it out, and here’s what I did:
My audio interface has two channels in and out. The basic idea behind what I wanted to do was to get my voice onto channel 1, and Skype onto channel 2, and then record those onto separate tracks in GarageBand.
The basic problem is that Skype output (indeed output from just about anything) is 2-channel stereo, so if I use that as the input to GarageBand, I’ve blown my chance to separate Skype onto one track.
Soundflowerbed to the rescue. This is a simple utility that lives in your OS X menu bar and lets you route channels from Soundflower to any channels you like on any of your output devices.
Soundflower (2ch) Channel 1 -> M-Audio Fast Track Channel 2 Soundflower (2ch) Channel 2 -> M-Audio Fast Track Channel 2
By sending both channels of Soundflower to channel 2 of the M-Audio Fast Track, I have a realtime mixdown to mono.
The next challenge is that while the Skype audio is now on the Fast Track Output Channel 2, we still don’t have anything on the Fast Track Input Channel 2. The fix for that is a TRS patch cable from the balanced channel 2 output on the back of the Fast Track to the channel 2 input jack.
The last hurdle is that you can’t try to monitor GarageBand with the Fast Track, because then you’ll be adding more signal to the Channel 2 output which is just going to turn right back around and be recorded on the Channel 2 input. Make sure you use the Mac’s built-in headphone output for GarageBand.
An optional step: you’ll notice that if you try to monitor your voice in GarageBand by turning track monitoring on, the latency is too long, and messes with your head (you hear your own voice about a quarter second after you speak, which will make you think maybe you’re drunk). You probably don’t need to monitor your voice, but if you want to, download a free app from Rogue Amoeba called LineIn, and set input to M-Audio Fast Track Pro and output to Built-in Output. You can still hear latency, but much much less. Just to be clear: you will have GarageBand monitoring off on your microphone track, and on for the Skype audio track.
Skype Audio output: Soundflower (2ch)
Skype Audio input: M-Audio Fast Track Pro
Skype Ringing: Soundflower (2ch)
GarageBand Audio Output: Built-in Output
GarageBand Audio Input: M-Audio Fast Track Pro
LineIn input: M-Audio Fast Track Pro
LineIn output: Built-in Output