Multiple USB Microphones in a single recording.

[weismanak]

I'm fairly new to Audacity, and currently I am using version Audacity 2.4.2 on a MacBook Pro running Big Sur (version 11.1). I typically use a Blue Yeti USB microphone to record my weekly podcast in Audacity on a single Stereo track. I would like to add a conversation from the local computer at the same time. I am unsure of how to add a second input, specifically from the local computer. I could pull the same "localized" audio from the output on another Mac computer using a 3.5mm output, and input it into the USB-C on this MacBook, creating a second input channel? How would you all configure this?

[billw58]

The first thing that comes to mind is to create an Aggregate Device in Audio MIDI Setup. This will be a bit of a kludge as the audio from the two sources will be mixed together before being presented to Audacity.

-- Bill

[kozikowski]

Aggregate Device. Someone said the latest Aggregate Device allows split channel recording, but it still asks which bitstream you want to use as Master. That becomes the "right" one and the other one may drift off time. If you have a long podcast, the two voice streams may end seriously out of sync.

If you have another Mac in there, why aren't you recording the second voice on that? Export WAV and Shuffle the sound file over to one machine and mix your brains out. It's a snap to solve sync issues with two separate tracks. Effect > Change Speed on one of them. Change Speed gives you every possible combination of matching methods. Percent Change, Beginning and End Times, Duration, etc.

Koz

[steve]

That becomes the "right" one and the other one may drift off time.

I've not tested extensively, but on modern Macs, "Aggregate Device" appears to do a pretty good job of keeping the devices synchronized.

I think what it is doing is checking the real time for each block of samples from each device, then if necessary, padding or trimming the blocks from each of the "secondary" devices to keep them synchronized. As the amount of drift is likely to be only a fraction of a sample per block, the occasional trimming or padding of one sample is invisible (inaudible).

My description above is largely conjecture, but the bottom line is that I don't see any noticeable drift.

[kozikowski]

Does it still ask?
Koz

[steve]

Does it still ask?

Does it ask what? What is "it"?

[kozikowski]

Which track you want it to use as "Master." It used to do that as you were setting up the Aggregation.

Koz

[steve]

When you create an Aggregate Device (in "Utilities > Audio MIDI Setup"), you select one of the device in your aggregate device as the "Clock Source".