Tip Top Tips: Monitoring Recording In Audacity

This month's tip comes from DaveCS.

I don't know how many people have a similar setup to mine. With my old stereo system, I had a phono input for vinyl, and a Line Out which I wired around the room to my computer. When the amp had seen better days, I saw a real bargain to replace it. However, it had neither a phono input nor a line out. I was able to get a phono-preamp, but the only way I could feed it to my computer without loss of fidelity was to make a little switch box, feeding the phono-preamp output to either the main amp or the computer. As a result, there is no sound in the room when I am recording, so I can't hear if the record jumps or ends. So first I tried an Audacity setting, Edit > Preferences > Recording > Software Playthrough of Input.

I found this to be disastrous. When recording, the record button often didn't work, and when it decided to record, the program either exited after a while (Audacity v2.2.0) or just stopped recording for no apparent reason (v2.2.1).

How could I monitor what I was recording? The solution was in the PulseAudio settings. However, I needed to run an command in a terminal to make "Loopback" available, which would allow the line input to play through, and another to stop it. The commands are:

On: pacmd load-module module-loopback latency_msec=5
Off: pacmd unload-module module-loopback

It was a simple matter in Xfce, adding them as extra commands on the Panel Launcher for Audacity. Now I can hear what is coming in through the Line input without using Audacity playthrough. Thus, Audacity remained stable and I got the recording done.

One little thing. While it was monitoring and recording at once, there was a slight distortion (crackling) in the computer speakers, but fortunately this was not present when I played back the recordings.

I found the hint here: https://unix.stackexchange.com/questions/263274/pipe-mix-line-in-to-output-in-pulseaudio

I hope this helps someone.