Along the same lines, these crazy fools are making oscilloscope music, where the song itself is the visual.

https://youtu.be/XziuEdpVUe0

"... and CTF challenge authors love to encode text into audio waveforms, which you can see using the spectogram view (although a specialized tool called Sonic Visualiser is better for this task in particular)."

https://raw.githubusercontent.com/trailofbits/ctf/master/doc...

Stenography is common, but usually it's just modifying the last bits of an image or hiding the extra payload after the image data. This is "drawing" within the audio spectrum, making the image out of audio that will be audible.

Steganography. Stenography is something else. :)

This gets me every. Time. Lol

Was this hidden in the audio or just some garbage noise?

The "Aphex face" manifests as an clearly audible weird abstract sound at the end of the track. It sits nicely in the mix, but it's also distinct from the actual music - I would say it comes across like a signature rather than a musical element. The other examples in GP's linked article made more effort to produce things that are both musical and paintings in the spectrum, especially the Plaid track.