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Oscilloscope

Optical Synthesizer Optical Synthesizer

Of all my ideas this is the one I am most proud of. This is because it sounds so good and because it works in a completely different way to other sound generators. I discovered it when I was playing around with a light sensor and seeing what waveforms I could pick up by pointing it at different light sources, I was viewing the waveforms on an oscilloscope. I had the eureka moment when I pointed it at the oscilloscope screen that it was connected to, creating a feedback loop. The line on the oscilloscope would now trace the silhouette of any shape placed on it's screen. I later realised that similar setups were used in the 50s.

The sound

The sound is really special, it has an organic turbulent quality because of the feedback loop constantly trying to follow the edge of the shape on the screen, but not quite doing it perfectly. I find it only sounds really beautiful when played at full volume through a vintage Marshall stack, this is how the 2 following sounds on this page were recorded.

speakerSong1.mp3 All the synths in this song demo are the oscilloscope.

speakerSong2.mp3 The lead sound here is the oscilloscope

(Both pieces of music written by Steve Santa Cruz)



How it works

Optical Synthesizer Optical Synthesizer

The oscilloscope is an add-on to an existing synthesiser, the synthesizer merely provides a frequency to scan the oscilloscope screen. A sawtooth wave is usually best for this as it scans at a constant speed, letting the pattern on the screen become the output signal, any other non linear wave like a sine would distort the pattern on the screen and the sound would be more harsh.

It has many modes of operation. I have used it to do ring modulation, phase modulation, analog sampling, sequencing, and lots of other strange things that don't have any conventional definition.

The videos below are a few examples of it's different modes.


Basic setting, sawtooth wave to vertical, light sensor feedback to horizontal.


Same as basic setting but sawtooth is sent through envelope before it is sent to the oscilloscope screen.



Same as before but audio is from sequencer/arpeggiator.


No feedback from the light sensor, the audio signal is just scanning a line, the square grid seems to make quite vocal sounds.



The vertical input on the oscilloscope is being fed by an above audio frequency signal, the horizontal is connected to the audio synth signal.


Same as before but using my fingers



This is very complicated and interesting. 2 different audio signals are being sent to the horizontal and vertical inputs.


Me setting up so you can see what equipment I am using.