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A low latency guitar effects processor suitable for running on a Raspberry Pi

by Audiophilip on 3/7/23, 3:03 PM with 142 comments

• by sklarsa on 3/7/23, 3:29 PM

  > Note that since the server program exposes an HTTP server you can actually navigate to the IP address of your PI from any device connected to the same wifi and control your pedal chain from there.

  That's a killer feature for me, hiding at the end of the README. I have a Fractal Audio FM3[0] at home, and the only way I edit my patches is using their editing software over a USB connection to the device. Adding the ability to program (and even control) my patches live over any wifi-enabled device is even cooler!

  [0] - https://www.fractalaudio.com/fm3/

• by metmac on 3/7/23, 4:09 PM

  While not a guitar effects box another project that does low latency audio things with an RPI at it’s core: https://monome.org/docs/norns/

  Open source version: https://monome.org/docs/norns/shield/

• by ghostly_s on 3/7/23, 11:25 PM

  Sweet, was just looking for something like this the other day. My use-case is not for guitar, but just to offload some fx processing out of a DAW - a friend and I have gotten into jamming recently, and while you can do just about any musical production task these days with a budget laptop and enough patience, where you quickly run into limitations is running multiple realtime effects. I'm not yet serious enough about it to start spending $ on effects pedals (which typically cost hundred of $ each), or even to have a clear enough idea of what pedals I would want, but I know enough about electronics to realize most modern ones are just a glorified arduino with a a 500% markup, so a budget-friendly programmable swiss ay knife pedal would be a dream.

  For my use-case the touchscreen is entirely unnecessary (programming it via a WebUI sounds more convenient anyway if you don't need to use it sans PC), which is inflating t he BOM by about 500%, and of course RPi4 is a uniquely poor choice of target platform at this particular moment in time, so seeing if it can run on a headless Pi Zero is definitely going on my endless to-do list. ;)

• by jamesgill on 3/7/23, 5:28 PM

  As an amateur musician, three things stand out:

  1. I'd have a hard time seeing that small screen onstage, and my big foot would likely mash the wrong effects button. Others might find it easier.

  2. There are tons of good, cheap effects boxes out there, and easy to find used. I like Pi boxes, but this seems like a homebrew replication of what's on the market.

  3. All good boxes are low-latency, in my experience. It's a fundamental thing I think most players need.

• by razerbeans on 3/7/23, 11:19 PM

  As others have mentioned, I think the interesting thing here would be understanding the latency for processing the signal. Anything in the single digit milliseconds would be fantastic! I know at one point I was looking into Raspberry Pi and ended up on Pedal Pi[0], though I couldn't get the parts I needed to make it work.

  I ended up using Teensy[1] and related audio shields[2] to get things working from a sound/acceptable delay perspective. But being able to get things going on a Pi would probably make more of the advanced input controls much simpler to implement simply from a OS support perspective (like in this project with the WebUI). The UI I'm seeing in this project looks great and it would be cool to potentially see something like kits/preinstalled images roll out for this!

  [0] - https://www.electrosmash.com/pedal-pi [1] - https://www.pjrc.com/teensy/ [2] - http://blackaddr.com/products/

• by snarfy on 3/7/23, 5:22 PM

  > A Low Latency Guitar Effects Processor

  What's the latency? I can't find numbers anywhere.

• by digitallyfree on 3/7/23, 4:13 PM

  I'm still patiently waiting for future digital mixing consoles to do all processing in software on inexpensive x86 or ARM processors. Currently due to latency and reliability requirements all DSP work is done on dedicated chips or FPGA which brings up the BOM and engineering cost. They often have a small ARM/Linux module which is used for the displays and network control.

  The CPU tech is here today, and modern general purpose processors do a good job of handling low-latency audio. Someone just needs to put all that together in a unified and stable package...

• by iamsaitam on 3/8/23, 8:32 AM

  A better alternative to the Raspberry Pi which is more suited for musical applications (and currently much cheaper) is the Daisy Seed by Electro-Smith[0]. You can program it in C++ / Pure Data / Arduino and Max/MSP Gen~. The community is very helpful and there are plenty of examples to start with. They also provide a few options to get started with some knobs/buttons. I'm not affiliated with them, just admire the whole ecosystem.

  [0] - https://www.electro-smith.com/daisy/daisy

• by honkycat on 3/7/23, 6:09 PM

  I've had some amazing ( horrible ) adventures in low latency music stuff lately. It has made me think about going back to the hardware side of music production. Previously I was an ableton-only dude.

  All of the vst plugins are CPU bound and even though i have a top of the line i7 and 32 gigs of ram, my computer slows to a crawl when editing even moderate sized songs.

  Specifically, there is an nvidia bug that introduces latency to real time audio, making guitar and other live performance unplayable.

  It really sucks! At least it has finally been ack'd (Increase in DPC latency observed in Latencymon [3952556]): https://us.download.nvidia.com/Windows/531.18/531.18-win11-w...

  This has been a problem for YEARS. Hopefully they will finally fix it.

• by kbr2000 on 3/7/23, 5:55 PM

  Well done!

  For those interested: a predecessor called the "Jesusonic" was once made by Justin Frankel (of Winamp and REAPER fame): https://www.cockos.com/jsfx/ https://wiki.cockos.com/wiki/index.php/Jesusonic_Documentati...

  :)

• by woudsma on 3/7/23, 3:28 PM

  Very cool, I've ordered a Raspberry Pi touchscreen this weekend and it should arrive today. I want to make a MIDI sequencer with it, or at least play with the idea. I hope my old Raspberry Pi can work with MIDI (over USB) without too much latency..

• by silveira on 3/7/23, 3:14 PM

  Any samples or videos of this working? I would like to have a feeling of the latency and how the effects sound.

• by rtatay on 3/7/23, 3:14 PM

  This is really cool. I may have missed it (am on my phone and just skimmed the readme) but what effects are available and can you build your own?

• by pengaru on 3/7/23, 10:12 PM

  I've found the RPi4B to be somewhat awful for low-latency audio usage.

  My particular use case is simply playing MP3s read from mmc through an MBox1 on USB.

  No matter how much irqbalance, isolcpus, taskset magic, it never gets absolutely perfect. It gets better, but there's always spurious delays exhibited as occasional pops and clicks in the audio output.

  I'm hopeful that [0] will improve the situation, but haven't had time to really dig into it let alone build a custom bleeding-edge mainline kernel - which I'm not even sure supports all the Pi4B hardware.

  It's asinine that an otherwise idle 4Cx1.8Ghz machine can't even play MP3s on a USB MBox1 flawlessly with zero special effort...

  [0] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin...

• by ushakov on 3/7/23, 5:42 PM

  Reminds me of NeuralPi, which uses ML models to emulate real AMPs

  https://github.com/GuitarML/NeuralPi

• by Diapason on 3/7/23, 10:14 PM

  https://mod.audio/ (I'm not affiliated - just a long time follower)

• by dontbesquare on 3/7/23, 3:15 PM

  This looks very promising. I'm interested in how to make effects and learn more about it. What a cool project!

• by WorkerBee28474 on 3/7/23, 8:21 PM

  From my understanding the Line 6 Helix uses two 450MHz SHARC processors, ADSP-21469. Other effect/amp modelers use more or newer of the same family[0].

  Can anyone comment about the relative processing power of a RPi vs the market solutions? Is the RPi theoretically good enough that a pedalboard could be completely modelled?

  [0] Interestingly, it sounds like SHARC chips were designed to be low cost processors for single use applications in guided artillery shells.

• by tastysandwich on 3/7/23, 11:16 PM

  > The root of it is the Transform function which takes an input signal, performs any kind of transformation, and returns an output. All input and output values should remain in the range [-1, 1] otherwise you'll produce some really gnarly popping and cracking.

  So you have to make all your own effects in code? It would be cool if it connected to something like Guitarix (open source) so you could use existing guitar effects. (Disclaimer: I've never used Guitarix, so it might sound shit)

  Btw, for anyone who doesn't play guitar, but is interested... Gone are the days of those huge pedal boards and having to buy 30 different pedals. Emulation is getting really really good. You can either buy a multi-effects pedal and use that onstage. Or if you're in the studio, NeuralDSP is software which can emulate basically any sound you're after. It's expensive though, but it sounds better than free alternatives like Amplitube.

• by ciroduran on 3/13/23, 12:05 AM

  Nice, I just installed this on a Raspberry Pi 3 with a touch screen I had around. Save for an issue when installing rtaudio (requires libasound2-dev in Debian), it went almost flawlessly. I'm guessing the RPi 3 can't handle realtime audio and graphics, as popping was frequent (although not annoying for the purposes of experimenting). The buttons did nothing, I'm afraid, but the web interface is ace!

  I'd love to write about this soon. Kudos to the coder

• by DeathArrow on 3/7/23, 3:51 PM

  I thought is hard to have low latency audio in Linux with stuff like PulseAudio.

• by ElijahLynn on 3/7/23, 7:46 PM

  There is also Pisound for low-latency guitar effect processor which is a hat for the Raspberry Pi. https://blokas.io/pisound/

  The UI, MODEP, is based on the Mod Devices work on their open source pedal (Originally Mod Duo) > https://mod.audio/.

• by Min0taur on 3/7/23, 5:54 PM

  This is a wonderful project, thank you for sharing your process! I'm excited to try making a cute/custom FX brain with this.

• by qqqwwweeerrr on 3/7/23, 5:14 PM

  This is awesome. I'd be really interested to find out if a Raspberry Pi can run an open source amp modeler like NAM (https://github.com/sdatkinson/neural-amp-modeler).

• by m12k on 3/7/23, 4:44 PM

  Very nice! A screenshot or two of the web UI would be a good addition to the readme

• by rerdavies on 3/7/23, 8:27 PM

  Also see: https://rerdavies.github.io/pipedal/

  which solves the problem with using a bar's Wi-Fi by using Wi-Fi Direct.

• by jojobas on 3/7/23, 10:47 PM

  What is he using for actual audio interface? RPi has something awful onboard and none of the pictures show anything external. USB would add 0.25ms latency just for being USB, best case.

• by worik on 3/7/23, 6:34 PM

  If you are interested in this see https://blokas.io/modep/

  Hosting plug-ins is a very powerful way to go.

• by 20after4 on 3/8/23, 3:59 AM

  Looks a lot like https://mod.audio/dwarf/ which I own and love.

• by atoav on 3/7/23, 8:48 PM

  Nice project, but nonway on earth I am taking anything with a breadboard and jumperwires onto stage — except maybe if I plan to make it part of the performance

• by 1024core on 3/7/23, 7:29 PM

  I'm guessing the harder part would be actually finding a Pi for this?

• by chaosprint on 3/7/23, 7:09 PM

  have to compare with Bela when it comes to latency

• by hendry on 3/7/23, 10:55 PM

  Surprised that a (local) Web call can be considered low latency. Isn’t this why people use grpc etc?