How To Draw Mushrooms On An Oscilloscope With Sound

August 14, 2017 | 09:00
How To Draw Mushrooms On An Oscilloscope With Sound
Images and sound by Jerobeam Fenderson
Here’s a classy amusement for summer. Especially if, like me, you thought that an old cathode-ray tube oscilloscope, being analog, is not made for “looking at music” (sic). Here a great old oscilloscope draws elegant animated geometric images on its screen, synchronized with music specially created for this. Even if it’s raised here to the realms of art, with a neat soundtrack, the principle is the well known one of Lissajous figures. Our more grey-haired readers may perhaps remember an Elektor project called “Spiroscope” published in the ‘70s (see attachment below).

Music on an oscilloscope in X-Y mode

Here the oscilloscope is a Tektronix D11 5103, known for its size and its brightness, but it works like any scope with an X-Y mode. Even digital and virtual scopes, at the price of a degradation of the graphics by artifacts of digitization and filtering.
The musical signals – or sound effects if you will (listening on headphones is recommended – for the neighbors and for your own understanding) are generated by an X-Y synthesis process which the author,  Jerobeam Fenderson, explains well on his YouTube channel.

One of the merits of these brilliant demonstrations is to remind us of the extent to which hearing is such a refined sense. The underlying capability of our brain to process an audio signal is vast. Usually the relationship between a complex audio signal and its representation on an oscilloscope is not that obvious. With the ear, it’s easy enough to distinguish between elementary waveforms (sine, triangle, square, sawtooth…) but when it comes to music or a voice, even the most faithful graphic representation of the electric signal tells us very little about what is happening at the audio level.
Fascinating geometrical patterns on an oscilloscope screen
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