Zoom and Pulseaudio -- audio distortion on audio run through zoom_combine

Solution 1:

I made the following changes in ~/.config/pulse but you can also put them in ~/.pulse if it doesn't already exist. At least on this system, pulseaudio runs as the user. No system configurations were being applied from /etc/pulse, so editing them made no difference.

~/.config/pulse/daemon.conf

resample-method = speex-fixed-7
default-sample-rate = 48000
alternate-sample-rate = 44100

Each of those 3 settings is completely essential. It sets the loopbackStream sample rate to 48000Hz so that it matches zoom combine and the hardware. Then, zoom combine will successfully resample from the application audio from 44100Hz to 48000Hz. speex-float is not appropriate. The sample type is fixed.

The source of that awful distortion came from switching sample formats during resampling and unnecessarily using a different sample rate in the loopbackStream. Set the default sample rate to match your hardware and alternate sample rate to match applications if they're different. Changing the resampling method alone did not produce perfectly clear audio.

I tested the speex-fixed-N resampling methods with music. speex-fixed-7 was where the high end starts to shine and cymbals are clear. Some people think speex-fixed-5 is adequate.