Just upgraded to a new Windows 10 computer and the latest version of Audacity.
With “OVERDUB” turned off, i cannot hear the earlier tracks.
With “OVERDUB” turned on, the earlier tracks flood onto the new track.
Not sure if this is related or not, but the mic signal is not registering onto Audacity. Phantom power is turned on, recording level on the Roland Quad Capture is up and registering on the meter, and the Audacity recording level is set at full gain (one).
This exact same set up worked perfectly last week. But - for some strange reason - it’s not working now. I was able to get the mic level fixed by going to: EDIT / PREFERENCES / DEVICES / RECORD. I changed “RECORD” from “MAIN (QUAD CAPTURE)” to “1-2 QUAD CAPTURE”. As i said, it worked perfectly last week. How the RECORD option got switched, i’ll never know.
But i am still unable to monitor preexisting tracks while recording a new track. I’ve been doing this for almost a decade, so why did it suddenly stop working?
OK, here’s is the way I picture you have your system configured.
On Quad-Capture:
- Microphone in port 2R (XLR). 48V turned ON if Condenser Microphone.
- Headphones plugged into Quad-Capture
- Direct Monitor Selected
- Mix: Playback/Input in center position
- Output adjusted so you can hear Microphone in your headphones.
On the Computer:
No other audio software should be running. There should not be any sound coming out of your main computer speakers. All of the sound should be coming out of your headphones which are plugged into the Quad-capture.
In Audacity:
Stereo backing music prerecorded and displayed in one stereo track in Audacity.
Transport > Rescan Audio Devices
Device input for Audacity: Quad-Capture 1-2; 2 (Stereo) Channels selected.
Device output for Audacity: Quad-Capture
Host: MME or WASAPI
OK, forget about recording for a minute. Play the audio track and make sure you can hear it through the (quad-capture) headphones. Adjust the Mix and Output levels as needed. You should also be able to hear yourself properly through the microphone.
OK, now stop the playback amd do your overdub recording. Everything should happen as before, but now Audacity should be recording a new stereo track - the left(top) channel of this new track will be entirely flat. This is OK.
You didn’t say what kind of microphone you are using.
Thank you for your assistance!
I’m using a Bruel & Kjaer Type 4011 Directional Microphone.
After setting everything as you specify, the signal is recorded onto the new track.
However, i am still unable to monitor (to hear) the previously recorded tracks while recording.
This is a condenser microphone, so you will, in fact, need 48V phantom power, so this setting is correct.
Congratulations! 
Bummer! 
I had been hoping we addressed this issue. OK, if you can monitor while playing the the track, then Transport > Transport Options > Overdub (checked) and Tranport > Transport Options > Software Playthrough (unchecked) should do it for you. Also try Record and Shift-Record.
Otherwise:
Can you hear the output from your microphone? If not, check the Output level on the Quad-Capture. Check the Mix adjustment. Adjust the microphone sensitivity level.
If you cannot hear the audio when you are playing there are a number of things to check. Check the Mix adjustment. Are the headphones working properly? Do you have sufficient signal in your backup music? Is it on Mute? You can try Generate > DTMF to generate some audio to playback.
I hope this helps.
Thank you so much. Suddenly it functions normally.
Not sure what i did differently. I generated a DTMF signal onto a new track and listened to the playback of that track, which appears normal.
After that, i put a check on OVERDUB and insured that PLAY THROUGH was unchecked.
Recording now works perfectly.
Before the DTMF, if i checked OVERDUB, the recording track had been flooded far beyond zero with both the new signal and the background track.
Now it is recording properly.
I’ll cross my fingers and send you a heartfelt appreciation.
Thanks for the update. Glad to hear everything is working for you now. 