Ohsillyscope waveform display

By David Crookes. Posted

Watch the official video for the Arctic Monkeys’ Grammy-nominated single, Do I Wanna Know?, from 2013 and you’ll see sound-waves vibrating in synchronisation with the percussion, lead guitar, and singer Alex Turner before turning into an animation.

It’s a simple yet compelling effect and it certainly struck a chord with music fans, surpassing more than a billion views on YouTube in 2020. “My favourite part of going to concerts is always going to be the visuals and the music video definitely inspired me,” says Thomas McDonald. It’s led to the creation of an open-source version of an oscilloscope which displays live audio as a waveform. Thomas calls it the “Ohsillyscope”.

The project allows Thomas to play musical instruments and see the tunes visualised as waves on a 64×64 LED matrix display. “After getting the LED matrix and playing around with it, I figured there would have to be a way that I could use it with my guitar and other musical instruments,” he explains. “It’s always really fun watching the live signal from synthesiser software, but I imagined I could make something more physical with the matrix.”

Live jives

The idea, he explains, boiled down to registering a live audio signal with a Raspberry Pi computer. “Down the line, I want to make some more complicated visuals that are reactive to the audio signal coming in,” he says.

It has involved connecting the matrix panel to an Adafruit RGB Matrix HAT add-on. “I have Raspberry Pi recognise the audio interface it’s hooked up to, and I’ve used Linux’s Advanced Linux Sound Architecture (ALSA) library to read the signal from the interface and place it into the C code running the LED matrix’s library,” Thomas says. “It’s sampling at the refresh rate of the screen, which makes a really cool visual.” Learn more at alsa-project.org.

The result is a project that can be taken on the road as a visual accompaniment to musical performances. “At first, I was thinking that I could have it work through MIDI [a protocol which lets musical instruments, computers, and other hardware communicate with each other], but the idea of needing to be hooked up to the software Ableton Live killed the motivation to write an entire library to do so. I wanted something that didn’t require being by a computer to represent music.”

Looking good

Thomas loves using his creation. “It’s small and portable – something you just plug in knowing that everything is set up,” he says. “The LED matrix HAT was made for Raspberry Pi, so it was a no‑brainer. It also helped that I had a couple of Raspberry Pi Zero computers laying around begging to be used.”

Currently, he’s hooked the Ohsillyscope to the PA system in his band practice room. “It picks up the bass, guitars and drums, making an interactive show for anyone watching,” he says. “The people we’ve shown the Ohsillyscope to so far seem to love it and once we start gigging more, it’s sure to get the band more attention.” We’re definitely sure that it’s going to look good on the dance floor.

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