Music hacks: guitar effects, and an electronic tuner

Regular readers will know that I’m a particular sucker for musical hackery involving a Raspberry Pi. I’ve got two really terrific examples to share today.

First up, here’s a guitar effects box from Pierre Massat. He emails to say:

I write a blog about how to make guitar effects with computers running Pure Data in real-time. When I first heard about the Raspberry Pi I thought it would be great if I could use it for the same purpose. It would only be much cheaper, and much smaller than my current laptop, and could fit in my hand-made stompbox.


Recent improvements in Raspbian have finally made this possible, and this makes me very happy! The Raspberry Pi is now actually capable of running rather demanding Pure Data patches in (quasi-) real-time (at least with a latency that’s low enough to play live with it).


I quickly assembled a small patch to test it and make a video to demonstrate that it actually works very well.

It is obviously not the use the RPi was originally intended for, but to me (and I’m sure to other musicians as well), this sounds like a revolution.


There’s no trick, the Pi really IS doing all the DSP work. A reader posted a comment to ask where the computer was :)


Pierre has blogged about the hardware setup, and has made some video of the box in action. The really sucky thing about my job is that I get to see all of this incredibly cool stuff, and don’t have any free time to emulate it myself. This is a project I have earmarked for trying out when I retire.

Great socks, by the way, Pierre.


Meanwhile, Blacktonedev on YouTube has been using his Raspberry Pi, a 7-segment display, a handful of resistors and a collection of leds to make an electronic tuner. The only documentation available is what he’s left on YouTube, but it’s pretty exhaustive, and I’ve copied and pasted it here for you under the video, We were really impressed by this project; if you’re reading this, Blacktonedev, please get in touch so I can credit you properly!

Hardware & equipment
Tuner is using 15 LEDs (7 red (lower half) + 7 red (upper half) + 1 green (center)) for displaying frequency and 7-segment display for displaying the matched note (dot in the bottom-right corner signifies a sharp note e.g. A#, G#, D# etc.). MCP23017 16-bit I2C IO Expander is used for controlling frequency LEDs, 7-segment display is controlled via GPIO pins on Raspberry Pi. Everything connected with resistors, jumper-wires and 840-contact BreadBoard (using Starter Kit-B for Raspberry Pi from A web-cam (Microsoft LifeCam) connected to Raspberry Pi is used for recording & analyzing audio.

Software & theory
Java is used for controlling everything. Pitch detection is done by Autocorrelation method inspired by John Montgomery’s great 5K tuner.

Photo of the tuner…

Dedicated to the whole Raspberry Pi community.

Raspberry Pi:
Theory (pitch detection + autocolleration):… +…
5K tuner by John Montgomery:…
GPIO equipment (skpang):…



Daryl Stark avatar

Nice! Would be cool if it was possible to create a loopstation using the RPI. A normal loopstation isn’t cheap and a RPI would be much more adjustable.

GuitarExtended avatar

I don’t see why it shouldn’t be feasible. Loopers aren’t very demanding compared to other DSP stuff. I guess the RAM would be the only real limit if you want many layers playing at the same time.

Rob V avatar

pi people, you are going to have to fix your format. When you quote someone it makes a very this column of text 20 characters wide that scrolls down a long way. its quite hard to read. Have you seen it on an external computer?

XTL avatar

blockquote {
padding: 0 0 0 1.5em;
margin: 1.5em 15em 1.5em 3em;
border-left: 5px solid #eeeeee;

Matbe that 15em margin among 1.5em ones is a typo. Leaving a massive blank squishes the text down.

Colin Cameron avatar

Indeed – on an iPhone the quotes are one word per line!

Jancis avatar

that .. guy .. plays … just magnificent!
loved sound of it.

Robert avatar

That looks pretty sweet!

RPMayhem avatar

Looks like I need to buy myself another Pi and get to work building a stomp box. :)

Adam Temple avatar

Nice! I am following these guys’ lead and created a full Raspberry Pi effects unit (vst/ladasp plugins). I am pretty far on the software/configuration side, and now I am starting to work directly on the raspberry pi for test. See progress at AmpBrownie.

mike avatar

hi i would like to order all the necessary items to make this pi guitar tuner except the raspberry pi itself. how many pins is the 7 segmnet here?thanks

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