Impulse is a bit of eye-candy for your desktop. It is a widget that displays a graphical spectrum analyzer on your gnome desktop. It is written in c and python and uses GTK and cairo graphics to generate the animation. the impulse library creates a pulse audio connection context that reads the output stream from pulseaudio in a thread natively which can then be read from python. You can specify impulse to either output the raw stream or output the fft of the raw stream.
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Bug #509082: Audio not detected for multiple outputs
Reported on 2010-01-18