I've been developing a nice plugin visualization idea together with Ardour co-developer Sampo Savolainen lately. Sampo originally had the idea of feeding white noise through an EQ plugin, and displaying a spectrum of this to see the frequency response. This way you could see what the plugin is actually doing, instead of some approximation of what it is trying to do. The idea is to update the graph every time plugin parameters are adjusted. This will probably be embedded in Ardour's plugin GUI at some stage (probably in 3.0).

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However, this approach had it's problems with getting a smooth graph. After a bit of thinking, I finally noticed we could simply use the impulse response of the plugin, and *drumroll* it works great! Sampo has cooked up a test client, which hosts a ladspa plugin and shows it's amplitude and phase response.

For anyone who knows his DSP, it should be pretty obvious that measuring the impulse response is only useful for LTI filters. However, another idea emerged from this one: Showing the difference between output and input (output_spectrum - input_spectrum) could be useful for non-LTI plugins. Plotting non-linear plugins like this should give valuable information about new signal components produced by non-linearities. However, selecting the parts of the signal to be used for the analysis is not trivial and will need quite a bit of thinking and experimenting.

To say a few words about Ardour development in general: 2.6 should be released any time now and 3.0 is moving forward fast. I finished a region export dialog for 3.0 today. It offers the possibilities to export the raw region output, region output with fades or track output.