This is a visualization based on on the monoscope output plugin from
alsaplayer.

The monoscope output plugin was written primarily by Ralph Loader.

This implementation is taken from alsaplayer version 0.99.54, at
http://www.alsaplayer.org/

Note: only one instance of this plugin may be created at a time: it has a
lot of static data.  This should be fixed (and it shouldn't be hard to do
so, either).