Hardware recommendations to record two separate tracks but keep them in sync over long session? (1st from local microphone + 2nd incoming from Skype)

Question

Situation:

• I'm teaching language lessons over Skype
• I'm recording "demonstration" sessions
• The basic pattern is:
  • (1) - the teacher gives a prompt
  • (2) - then the student thinks for a second then answers
• This pattern repeats for an hour or two each session
• I need to record the two tracks separately, but keep them in sync over the whole session

When I say, "keep them in sync",
I don't mean compensating for the lag of the VOIP connection;
That lag is very minor (and constant anyway).

What I mean is:
I just want to record the teacher and student audio to two separate tracks
but keep them sync'd up exactly the same way I originally hear them on my end.

So the two tracks are:

• Teacher:
  • this is me
  • local, outgoing
  • coming from an external microphone that has two outputs: a USB output and an analog (both outputs can be used simultaneously) (this microphone)
  • currently, I'm using the USB output to send over Skype, and not using the analog output at all (although it worked fine when I tested it earlier)
• Student:
  • incoming audio from Skype

I've been recording the tracks on the same computer that's running Skype
(through ffmpeg and pulseaudio on linux)
but the tracks drift out of sync.
(And I don't believe there is a software solution to that with the setup I'm stuck with.)

So I want to get some new, separate hardware to completely sidestep the software stack.

That is, I'd like to continue using the current computer for Skype,
but record both analog tracks on a separate piece of hardware.

So I think I want to do something like:

• tap the analog output going to my headphones (the student track) through a headphone splitter

and

• tap the analog output from the microphone (the teacher track)
  (again, currently, I'm not using the analog microphone output; only the simultaneous USB output to feed into Skype)

and

• feed both analog inputs into a new, separate piece of hardware to be recorded in sync

(
Again,
by "in sync" I mean that I want the rate of the two tracks to not gradually drift apart over the session.
*I just want them to stay at the same rate I originally hear them at on my end;*
nothing to do with compensating for the network lag over Skype.
)

So I want some hardware that can take two separate analog inputs,
and can reliably record them in sync, as two separate files.
(
It would also be fine to record two separate channels in the same recording (like left/right),
so long as the tracks don't get mixed together.
)

Now, I could probably build something like that myself...
for instance, take something like:
this Raspberry Pi
and put it together with something like:
this soundcard
and then fiddle around for a week figuring out good softward setup to run on it...?

But ideally, can anyone recommend some straightforward, reliable hardware that's already set up like that, that I can just buy?

Answer 1

On Linux, you can use the Ardour DAW, it will record the separate tracks synced to it's internal software time-code.

It should be trivial to route the audio from skype into Ardour using Pulseaudio (it might be easier with Jack Audio) as well as the digital signal from your mic.