I've added support for OpenGL to Snd -- there's an example of a spectrogram in grfsnd.html; the configure switch is --with-gl. Also gl.c is a set of GL/Guile bindings in the same style as xm.c and xg.c. Currently works in Motif only (and of course there are a million things-to-do -- there's a partial list in snd-chn.c around line 1970).