I'm not 100% sure but the original link says

The audio processing did not record people through their microphones. Instead, it generated and processed an inaudible signal, then measured small, repeatable differences in the way a browser and device handled it.

Oh! They have a link to this -> https://ritter.vg/blog-webaudio_alibaba.html

Which makes it sound less scary, and not very effective against FF with fingerprint protection turned on. FF is working on mitigating it. Maybe Chrome and Safari can protect too. But it's also not quite a nothing-burger. Even a weak signal, is useful b/c lots of weak signals combine into a strong signal.

Everything contributes to the fingerprint. Even if everyone falls into say 2 buckets, that's still one bit you didn't have before.

Apparently not, and it works when the device's audio is muted.

The AliExpress website was found processing a fixed audio waveform and examining the resulting numerical values. Tiny differences can arise from the browser, operating system, CPU behavior, audio hardware, and drivers. When combined with other signals, they become another input that can contribute to a browser or device identifier.

Investigation of the page’s code reportedly found audio-processing graphs that were set to zero volume but remained connected to the system audio output. That explains why a user could hear nothing, and why muting a browser tab would not necessarily prevent the processing. All the relevant work was occurring within the Web Audio graph rather than through a conventional media player.

Wasn’t the AliExpress guy kidnapped by the CCCP a few years ago, and eventually released back into his former role? What was up with that?

Edit: https://www.bbc.com/news/technology-56448688