Raspberry Pi for guitar modelling, anyone?

[panhardleft]

Probably like everyone here on this forum, I've been looking into NAM lately. Not because I'm unhappy with my Helix LT, no, but somehow the quest for tone is never over. I definitely didn't want to use my PC, so I fired up my iPad again. And yes, it's great what's happened recently: TH-U remains great, but now also opensource stuff like Chowdhury DSP BYOD, with which you can also run NAM models, and then especially Tonex and Gigfast Lite. But... they all eat up resources, Tonex is totally buggy and Gigfast Lite keeps crashing as a plugin in Loopy Pro.

So I remembered that I had recently bought a Raspi (4B with 2G RAM), but I hadn't touched it yet for fear of falling into another time consuming rabbit hole of tinkering... and... of course I fell into it. First of all, I had to remember the basic Unix commands that I hadn't used in 20 years, and then I had to realize that there is a huge Unix audio community and everything is incredibly confusing and then audio under Linux: alsa, jack, pulseaudio, pipewire... A few days later I had a first overview (if that had been working time for a client, I could have bought a box full of Dimeheads). Whatever. Then I found some possibilities, tried Modep with Patchbox OS - unfortunately too resource-hungry, as is Zynthian

And then a few days ago I found Pipedal (https://rerdavies.github.io/pipedal/): A standard PI-OS installation, install Pipedal, two or three commands to get around a few bugs (that seems to be mandatory in this world) and you're done! Pipedal is a general lv2 host with a few effects and amps already built in. It already includes a version of the NAM plugin (https://github.com/mikeoliphant/neural-amp-modeler-lv2). Super stable and, what's more, high-performance. Great minimalist GUI. Pipedal installs a web server so you can control it from your mobile. You can use almost any profile (the only ones that don't work for me so far are @Slammin Mofo's high accuracy profiles).

I also found another great lv2 Nam plugin: Ratatouile: https://github.com/brummer10/Ratatouille.lv2, runs perfectly under Pipedal. With Ratatouille you can load two profiles in parallel and blend them seamlessly without increasing the processor load (you get two for the price of one). So you can go seamlessly from clean to crunch.

Yesterday I connected the Pi to the Helix and was impressed. Works perfectly. Round trip latency of 5ms - mind you, that's the full latency, measured with a loopback cable and a complex Helix preset. So Helix + Pi. My Helix can now do NAM! For 60 Euros! I'm thinking about buying a Pi 5 now, let's see how it runs

I would really like to know if others here are playing around with a PI (@Sedaxel ) and how you are using it!

 

[eggpl@nt]

I’ve been following the Pi Stomp from Tree Fall Sound. I don’t have any experience, but this concept is very much on my radar.

 

[Sedaxel]

I would really like to know if others here are playing around with a PI (@Sedaxel ) and how you are using it!

Yeah... The Pi can work perfectly.

I tried PiPedal, but ended up giving up on it because my Pi was always bouncing in CPU usage (jumps from 50% to 90% continuously without a reason).

A little later, I discovered Mike Oliphant's Stompbox, which is essentially the same as PiPedal, but I liked much more the GUI and effects. Also, Mike was of great help to getting it working, and my process helped to fix some bugs too.

I then discovered that my Pi, for whatever reason, makes those CPU jumps anyhow... It wasn't PiPedal's fault. And found out that forcing the CPU to be constant at the max frequency (instead of letting it go down and up depending on the load) solved completely the issue. Then it became stable.

Mike also added a fantastic noise gate when I told him that hi gain captures were noisy. Seriously, such a great work in no time.

As I needed to make some theatre gigs, I didn't dare to use the Pi and went with a normal rig. I still have to install the hotspot app to be able to control it out of my home WiFi... And I suspected that it would take me time (I'm not a Linux expert, every little task is a challenge for me... I'm proud of had been able to get there with all these software). But I could perfectly hook it up with my Boss ms-3 or any other midi controller.

One more reason for me to go with a Nano Cortex instead of the Pi (NAM) was that I wanted to try consistent captures (in terms of input gain), and NAM is not still on par in that regard. It's getting there, it's getting standardisation in latest updates. Let's see what I do in the future.

 

[SonVolt]

Is this just for fun I guess? Seems like a lot of time and work to get an inferior product.

 

[Sedaxel]

Is this just for fun I guess? Seems like a lot of time and work to get an inferior product.

Well... Inferior in which sense?

It's partly for fun, yeah. But I'd not say it's inferior... At least not tonewise. Plus, you got the advantage to choose your interface, and the possibility to customise everything, since it's actually a computer based rig.

It requires time to getting it up and running, and to have some IT skills, yes.

 

[SonVolt]

I just assumed it wouldn't sound as good as a professionally designed modeler from someone like Fractal for example.

 

[Sedaxel]

I just assumed it wouldn't sound as good as a professionally designed modeler from someone like Fractal for example.

It'll sound as good as any other NAM player. If that's better or worse than fractal is a subjective thing, I guess.

 

[pablo retamal]

And what is the temperature of the CPU at maximum working speed?...how do you solve latency problems without DSP...is it an advantage of ARM?... Risc?

 

[quadgear]

Yesterday I connected the Pi to the Helix and was impressed. Works perfectly. Round trip latency of 5ms - mind you, that's the full latency, measured with a loopback cable and a complex Helix preset.

Is that the round trip latency of from PiPedal audio input to PiPedal output?

What are you using for DAC and ADC (i.e., audio interface)?

 

[panhardleft]

Is that the round trip latency of from PiPedal audio input to PiPedal output?

What are you using for DAC and ADC (i.e., audio interface)?

Thats Helix in to Helix out - Helix ist the interface for the Pi. I used a normal Preset and added the Pi vi a USB

 

[panhardleft]

Is this just for fun I guess? Seems like a lot of time and work to get an inferior product.

Good point!! That's exactly where I started - falling into a rabbit hole just for fun. But then I realised that the Pi is a serious platform for audio. I actually just wanted a Nam player for my Helix - IOS options like Tonex and Gigfast just crashed. When I tried the Pi, I realized that there are really professional alternatives that run stable and are really gig-capable. However, you have to wade through a mess of different approaches
So I wanted to ask who has experience from a guitarist's perspective. I'm not a Pi/Linux specialist, but an amateur living room guitarist who still suffers from GAS.

 

[panhardleft]

And what is the temperature of the CPU at maximum working speed?...how do you solve latency problems without DSP...is it an advantage of ARM?... Risc?

Sorry that I don't have answers to this: I just used a Pi out of the box. Completely end user perspective. And I was completely surprised how good it worked!

 

[panhardleft]

Yeah... The Pi can work perfectly.

I tried PiPedal, but ended up giving up on it because my Pi was always bouncing in CPU usage (jumps from 50% to 90% continuously without a reason).

A little later, I discovered Mike Oliphant's Stompbox, which is essentially the same as PiPedal, but I liked much more the GUI and effects. Also, Mike was of great help to getting it working, and my process helped to fix some bugs too.

I then discovered that my Pi, for whatever reason, makes those CPU jumps anyhow... It wasn't PiPedal's fault. And found out that forcing the CPU to be constant at the max frequency (instead of letting it go down and up depending on the load) solved completely the issue. Then it became stable.

Mike also added a fantastic noise gate when I told him that hi gain captures were noisy. Seriously, such a great work in no time.

As I needed to make some theatre gigs, I didn't dare to use the Pi and went with a normal rig. I still have to install the hotspot app to be able to control it out of my home WiFi... And I suspected that it would take me time (I'm not a Linux expert, every little task is a challenge for me... I'm proud of had been able to get there with all these software). But I could perfectly hook it up with my Boss ms-3 or any other midi controller.

One more reason for me to go with a Nano Cortex instead of the Pi (NAM) was that I wanted to try consistent captures (in terms of input gain), and NAM is not still on par in that regard. It's getting there, it's getting standardisation in latest updates. Let's see what I do in the future.

I have to try stompbox!!

 

[Sedaxel]

And what is the temperature of the CPU at maximum working speed?...how do you solve latency problems without DSP...is it an advantage of ARM?... Risc?

I have it with an aluminium case/sink and a little fan. This way, temperature stays at 40C.

My interface is a Hifiberry. RTL is 3 - 3.5 ms (measured by me with Reaper).

With an Audient Evo4 it has around 5 ms.

Maximum working speed in my setup is 1800 (standard setting of the Pi for turbo mode on).

 

[Sedaxel]

Thats Helix in to Helix out - Helix ist the interface for the Pi. I used a normal Preset and added the Pi vi a USB

This is really surprising... I've read here and there that Helix had quite bad RTL numbers when used as audio interface! How did you measure?

By the way, I did that same setup with a Mooer GE250 (which wasn't optimal, because it works at 44.1kHz, while NAM captures were created at 48kHz, but I was just laying tests), and my RTL was also around 5ms.

 

[Sedaxel]

I have to try stompbox!!

It's impressive. Mike did such a great job. You can find his project in GitHub.

 

[panhardleft]

This is really surprising... I've read here and there that Helix had quite bad RTL numbers when used as audio interface! How did you measure?

By the way, I did that same setup with a Mooer GE250 (which wasn't optimal, because it works at 44.1kHz, while NAM captures were created at 48kHz, but I was just laying tests), and my RTL was also around 5ms.

Pipedal has a tool pipedal_latency_test. To use it, you need to connect the input of your interface to the output. It will then play test tones that are used to measure the latency. I connected the input of the Helix to the output, loaded a (relatively complex) preset, sent its output to USB, then recorded the path again with USB In and measured it - these are the results:

panhardleft@pipedal:~ $ pipedal_latency_test hw:HELIX
Device: hw:HELIX Rate: 48000

Buffers
Size 2 3 4
16 198/4.1ms 214/4.5ms 231/4.8ms
24 215/4.5ms 239/5.0ms 262/5.5ms
32 242/5.0ms 281/5.9ms 319/6.6ms
48 281/5.9ms 322/6.7ms 382/8.0ms
64 331/6.9ms 395/8.2ms 458/9.5ms
128 458/9.5ms 586/12.2ms 721/15.0ms

(sorry, this should be a table)

24 / 3 Buffers is completely usable...

 

[CorrosiveMatter]

For the money you can get a way more powerful computer now, Pi were cool back when you could buy one for $35, now they are still low performance but not as cheap. I would think you could buy mini pc's and have less limitaitons and better performance.

 

[toneseeker911]

This sounds like I need a PhD.

 

[Mike Oliphant]

This sounds like I need a PhD.

This kind of thing isn't for everyone. It is more for people who are interested in what goes on under the hood and/or want more control over their setup.