wavdraw is a nice utility written on top of btprnt that draws a waveform of a mono wav file.
wavdraw exists as both a standalone commandline interface and as a janet function.
to use the CLI:
monolith wavdraw in.wav out.pbm
This will generate a file called out.pbm.
The pbm file format can then be converted to png using ImageMagick:
convert out.pbm out.png
The woven source code for this program can be found at wavdraw.c.
Someday, words for using wavdraw in Janet will exist here.