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

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

#91

Post by razerbeans »

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/

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

#92

Post by ghostly_s »

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. ;)

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

#93

Post by renewedrebecca »

unwind wrote: post #70
WorkerBee28474 wrote: post #67

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 sing…

According to Analog's product page [1] for the ADSP-21469, it delivers 2.7 GFLOPS at 450 MHz. And Wikipedia's page of all the RPi models says that the latest (4B) manages 8 GFLOPS at around 1.8 GHz. If that means that the answer to your question is "yes" or "no" is unfortunately a lot harder to Google and/or figure out. I would assume that the SHARC-based devices run on the metal, whereas most applications for the Ra…

I'd love to see one of these Raspberry Pi guitar FX projects run on bare metal or a RTOS instead of Linux.

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

#94

Post by PaulDavisThe1st »

digitallyfree wrote: post #18

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 genera…

> I'm still patiently waiting for future digital mixing consoles to do all processing in software on inexpensive x86 or ARM processors.

Harrison Consoles have done this for more than 10 years.

I cannot confirm this in the same way, but I think it also likely that both Lawo and Studer digital consoles do this, and also possibly Allen & Heath. All 4 companies run Linux internally on their consoles.

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

#95

Post by nick__m »

ghostly_s wrote: post #92

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…

I use an ESP32-A1S board for that. I use this project https://github.com/pschatzmann/arduino-audio-tools/ and the platformIO vscode plugins.

Have a look at this example to see how easy using that library is : https://github.com/pschatzmann/arduino-audio-tools/blob/main...

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

#96

Post by PaulDavisThe1st »

londons_explore wrote: post #53
TylerE wrote: post #22

Earlier quoted context omitted.

Modern CPUs are great if your watt (and thus thermal) profile is unlimited. Not so great when they aren't.

Most processing of audio isn't CPU performance limited... For most realtime audio mixing, it doesn't matter if you use 1 watt or 10 watts for your CPU - the big speakers will easily be drawing far more, and the performers time will be costing far more than the electric bill anyway.

> Most processing of audio isn't CPU performance limited

Processing, mostly true (though there are still some reverbs that can chew an awful lot of cycles).

Synthesis, however, is a different story. That is definitely CPU performance limited once you get into substantial numbers of voices/tracks/synths.

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

#97

Post by PaulDavisThe1st »

Diapason wrote: post #82

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

This should really be at the top of the thread, since it is fundamentally a commercial version of (and which also substantively predates) the project in TFA. Note that most of the technology in a mod is FLOSS (if not all of it).

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

#98

Post by PaulDavisThe1st »

DeathArrow wrote: post #9

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

PulseAudio is an audio server aimed at desktop applications. It has nothing to do (or offer) low latency audio work, and would never be used for it. ALSA is the driver layer on Linux, and it can go as low or lower in latency terms as the audio driver layer on any other platform.

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

#99

Post by prima-facie »

unwind wrote: post #70
WorkerBee28474 wrote: post #67

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 sing…

According to Analog's product page [1] for the ADSP-21469, it delivers 2.7 GFLOPS at 450 MHz. And Wikipedia's page of all the RPi models says that the latest (4B) manages 8 GFLOPS at around 1.8 GHz. If that means that the answer to your question is "yes" or "no" is unfortunately a lot harder to Google and/or figure out. I would assume that the SHARC-based devices run on the metal, whereas most applications for the Ra…

There's also a real-time version of the Linux kernel which is meant for exactly this type of application.
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