The Windows version of Ardour does not support separate I/O devices (unless they are word-clocked synced).
Keep in mind that VirtualBox is not real-time safe. It is not suitable for recording. There will be dropouts, not to mention the latency of the virtual soundcard back to the physical one is rather long (and undefined, so overdubs won’t align).
Why not run the Linux version natively? That is a lot more robust and reliable.
Also Ardour/ALSA (on GNU/Linux) does support separate devices for I/O.
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PS (Edit):
As for the original issue: Is the track still record-armed (Monitoring Input, not Disk)?
Does the meter in the mixer-window move and show a signal when you play?
I use virtualbox because my Tascam US-122 is no more supported by Linux: the driver freezes the OS.
About the two soundcards. Why you say that two cards are not supported? Ardour allows to select them: the Tascam for recording, which works as expected, and the builtin one for playback, which works for the imported MP3 track, and NOT for the recorded track.
The two sound-cards have different internal clocks. They will slowly drift apart in time and eventually that will result in audible glitches (long explanation in the Ardour FAQ).
Can you show a screenshot of the Mixer Window? That may shed some light (monitoring, connections, max-signal level…)
That sounds like a bug, have you reported it to the ALSA-team?
I posted it to the ALSA mailing, but I did get any answer unfortunately. There are two already opened bug id=203587 and id=208127 . I added my issue to them…
The two sound-cards have different internal clocks. They will slowly drift apart in time and eventually that will result in audible glitches.
I read the FAQ, but if I use one of the two card only for recording. Why the internal one plays only the MP3 track?
Ideally you’ll increase the gain on the analog side, once the signal is digitized it does not matter when gain is applied (before or after recording).
By default Ardour records the input as-is, but you can change a track to wet-record to
apply plugins or gain-staging before the data is written to disk:
You can use the trim-contron (knob top-right) or a plugin “ACE amplifier” (comes with Ardour).
To ask the obvious; are you using the 2nd input of the device that can be changed to Hi-Z (instrument/guitar) impedance?