Additive synthesis using the Web Audio and Web MIDI API. Works in Chrome and Firefox. Use a MIDI or QWERTY keyboard to play the synth.
The PADsynth technique works by running the inverse FFT on a frequency spectrum profile determined by the synthesis parameters. Frequency spread (or "bandwidth") is one of the key parameters; turning it up results in a rich chorus/ensemble sound.
The output is a time domain waveform. Every time the parameters are adjusted, the wavetable must be recalculated.
Fortunately, with a short wavetable, this happens fast enough to allow interactive performance in a web browser.
Many thanks to Paul Nasca, creator of the PADSynth algorithm.