Audio: low-frequency crackle or saturation heard in the editor, possibly on loud input

[EtienneLescot]

While testing the audio changes of #898 in the editor (2026-09-30), the maintainer heard a low-frequency crackle or an odd saturation in the sound. It is not caused by #898: it was heard before those changes. It may happen when the input level is loud, but that is only a suspicion for now.

Not known yet

• Whether it is in the recorded file itself or only in the editor's playback.
• Which source it comes from: microphone, system audio, or the mix of both.
• Whether the exported file has it too.

How to isolate it

1. Play the original media file in a neutral player (VLC, ffplay). If the crackle is there, it comes from the capture.
2. Measure the level of the file: ffmpeg -i <file> -af volumedetect -f null - (a max_volume at or near 0 dB suggests clipping) and ffmpeg -i <file> -af astats -f null - (look at the peak and clipped-sample counts).
3. Compare the editor preview with an export of the same project. Crackle only in the preview points at playback, only in the export at the encoder or the mix.
4. Record the microphone alone, then system audio alone, then both, at a low and at a high input level, to see whether the mix or the level triggers it.

Places to look once it is isolated (hypotheses, not verified): no gain or limiting when the microphone and system audio are summed, capture gain, resampling, and the AAC encoder at high levels.