CRT Audio Visualizer
A story from sounds to shapes
safety notice
cathode-ray tubes operate at dangerous high voltages and can retain charge even when unplugged. this experiment was conducted with proper precautions and should not be attempted without expertise in handling high-voltage electronics. the purpose of this article is to share an artistic and conceptual exploration, not a step-by-step guide.
when we first met, we immediately started experimenting with sound and machines together.
the particular field we were most naturally drawn to was cymatics, the technics of sound visualization.
that’s where our name comes from.
we always thought that the shape of a sound was key to better understand it.
our first cymatics experimentations were using water, sand or even a laser connected to a speaker. the waveforms were made visible due to the sound vibrations travelling through materials.
the resulting patterns were mesmerizing, always different for every sound and every material.
certain shapes kept coming back, and we found out later on that they were called Lissajous figures.
we spent hours admiring them, they influenced us deeply, and can now be found across many of our designs.
we were able to draw these figures on our first visualizers using different instruments, but we wanted to push the experiments further, to be able to control the sounds and their shapes more precisely.
in order to do that, we needed our own, custom sound generator and our own portable audio visualizer.
the sound generator we made is an early version of ALT: 6 oscillators, frequency sliders, and a filter. no quantizer, no delay, no modulation.
the perfect tool to draw beautiful shapes.
the audio visualizer is this custom CRT.
how did an intercom become an audio visualizer ?
our workshop is a place full of curiosities.
old cassette players, prototypes, homemade effect pedals, and amongst them was this CRT intercom.
CRT technology is fascinating. it’s basically a canon that shoots millions of electrons onto a panel full of phosphor, making use of human persistence of vision.
it is a fantastic and very eccentric way to display an image when you think about it.
it is fully analog of course, meaning it’s hackable. the canon has 2 directions, vertical and horizontal which is perfect for our audio generator which has 2 channels, left and right.
let’s make these electrons dance
we started by reverse engineering our intercom to identify the electron gun inputs and check the useful features we could keep.
then, how do we connect our synth to the CRT? by using a simple audio amplifier module. the right and left speaker outputs of the amplifier are wired straight to the electron gun horizontal and vertical inputs and that’s it.
the amplifier had a bluetooth receiver and a stereo jack input. we hacked it to get separate left and right inputs and a thru stereo output. we laser cut a plexiglas faceplate to make it pretty and all that made us quite happy.
this is where the magic begins
the shapes displayed on the video are some of the typical Lissajous figures we can get by detuning two VCOs. one is fully panned left, the others are fully panned right, and we can see them harmonize and create harmonious shapes when reaching certain frequencies.
the creation of these shapes happens under several conditions, including parameters such as a coefficient between the two frequencies of the oscillators but also from their phase shift.
the ratio influences the number of curves while the phase shift influences their direction and positioning.
perfect ratios and zero phase shift tend to create basic shapes like straight lines or circles, while the opposite (like a 5/6 ratio and a 3π/4 phase shift) creates more complex ones.
we are just scratching the surface here but that link between mathematics and sound is something that resonates with us very deeply.
this CRT might be another machine that asks questions and sound may very well still hold answers but we will continue.
from our first experiments of sound observation using sand and water to the creation of a CRT audio visualizer, this navigation between the invisible and the visible, between the abstract and the physical, is what led to the creation of cyma forma.
