I've been saving spectrograms as png files. They're 60 pixels per
second horizontally and 5 bands per half-step vertically.
Each pixel is a 24-bit number. This covers 10*log10(2^24)
dB=72.24dB, which is pretty good. I guess I could use the alpha
bit to kick it up to a 32 bit number (96dB) but I like the fact that
it's human readable: