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