I’m using sox to record the audio produced by the system (i.e. from the OS and other running apps), but the recordings sound very quiet.

I first create a virtual input/output device using Blackhole (https://github.com/ExistentialAudio/BlackHole/) or Loopback (https://rogueamoeba.com/loopback/). I then start playback of a file using iTunes, and start recording thus:

rec --rate 44100 --channels 2 --no dither test-output.aiff

(Note that this spits out the following error messages:

rec WARN formats: can't set sample rate 44100; using 48000
rec WARN formats: can't set 2 channels; using 16

However, test-output.aiff ends up being a stereo file at 44.1 kHz)

test-output.aiff properly records system audio, but the mean amplitude is about half the mean amplitude of the original sounds I played back. 

Any thoughts? 

Thanks

Ariel