Harmonic distortion of output signal
I'm running Rhythmbox v3.4.4 on Ubuntu Mate 22.04.1 LTS using Pulseaudio v1:15.99.1 (as shown in Synaptic) and Pulseeffects v4.8.4. I tested audio effects setup by monitoring audio spectrum with internal Pulseeffects tool, which apparently uses uniform window, and Baudline analyzer, which can apply window function. Baudline was capturing output of system audio monitor source. I played single sine wave sampled at 44100 and 48000 Hz and encountered harmonics of significant amplitude at frequencies which are integer multiple of major sine wave. I made a screen capture to show how results were obtained. I checked that system audio volume doesn't affect captured stream and that my test sine was played without clipping.
I used following command to launch Baudline as it is not working natively with Pulseaudio:
parec --channels 2 --latency=10 --rate=48000 --device=alsa_output.pci-0000_00_14.2.analog-stereo.monitor | /path/to/baudline/baudline_1.08_linux_x86_64/baudline -stdin -channels 2 -samplerate 48000 >> /dev/null 2>&1 &
I guess that such distortion should occur.