FilterOrgan is a VST/AU effect plugin which adds bandpass filters to your audio track real-time, based on the MIDI notes it receives. The filters' frequency is tuned to the received MIDI notes' frequency so you can play chords and melodies with the filters.
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CamTheremin is a freeware program simulating the instrument "theremin" with a webcamera: Touch the sensor lines (drawn into your webcam's picture) to control pitch and volume of the generated sound.
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