7 'unknown' -- because they are MIDIs, or tracker module files like .nsf and .sid - although there is also one .wav there, but it was programmatically generated and so maybe is lacking headers?

34 @ 24 kbps -- mp3s, from a single large album of chiptunes. The creator claims that low bitrates better match the chiptune sound and ethic.

1 @ 127 kbps -- an mp3 from a single album of very experimental (and to be honest, very dissonant) chiptunes; each song in that EP has a weird bitrate, so I will list the rest here: 128, 133, 134, 135, 135 again, 138. Other albums from that artist are a more normal uniform 128 kbps.

159 @ 128 kbps -- including the aforementioned.

4 @ 160 kbps -- from three separate albums, but all chiptune, so maybe a particular tracker exports at this quality?

558 @ 192 kbps -- 192 is 2^6*3 and is by far the most common here. Several genres, many albums, I think all mp3.

1 @ 199 kbps -- an mp3 rendering of a .sid, I think.

5 @ 256 kbps -- from 3 chiptune albums by two artists.

1 @ 320 kbps -- a standalone 'liquid dubstep' homage to Beethoven. Also the only file I have [mp3] that has metadata reporting beats per minute (140) besides two chiptune albums by the same artist, the contents of which are all 100 bpm.