The Reverse Oscilloscope now functions as a reverse-spectrum synthesizer. However, it currently can only create harmonic, periodic signals.
When I refer to a spectrum, I mean a graph of Fourier components of a signal. When I say a spectrogram, I'm referring to a 2D image that shows how those components vary with time.
The simplest reverse spectrum is a set of drawbars - here's the standalone version of my drawbar sim, if you're too lazy to figure out the Reverse Oscilloscope. The drawbars basically represent an upside-down Fourier spectrum with no phase data.
So, as promised, I've uploaded some of the early reverse spectrogram experiments. They come with no guarantee! Frequency is on the vertical axis, pointing up, time on the horizontal heading right. Press any key to play the sound. They probably only work in chrome.
Spectrogram iFFT - The harmonic one, i.e. only integer harmonics of the buffersize can be created. Spectrogram Render - The dumb-sum one, which has ideal behaviour but you have to wait a relatively long time for the rendering to take place. Spectrogram Vector - Pseudoadditive synthesis type stuff, rendered on each mouseclick. You can change the multiplier in the query string, for instance by appending ?0.5
I've talked some more about the problems with these and the phase issues at the end of the reverse oscilloscope project page.
There are more of these that I should post but they're even messier, and none of them are exactly what I wanted to create. Still, many interesting noises can be created.