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Comment by DeathArrow | Hacker News Reader

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

Nah, low latency audio is absolutely possible, but not necessarily using pulse audio. Using either Jack for the low latency stuff has been the advice for years, but with the advent of pipewire you can mix and match without too much difficulty.

A quick skim didn't turn up what audio backend this project is using, but I'm using patchbox with modep on my Pi4 as a bass pedal board and it's pretty much flawless low latency. I do need to add a fan to my pi since it's mounted underneath a pedal board and doesn't get quite enough air though.

Sep 2 of the build instructions says it requires RtAudio.

RtAudio is just an API wrapper which calls JACK, Alsa, etc behind the scenes and does not add latency, just the overhead of a couple c++ method calls

what is the latency of a raspberry pi running this type of software? can't find figures anywhere

I also wonder about the latency of the behringer interface. I've had one before, the sound quality is pretty good for entry level high-fi audio, but when I've run the audio into a DAW and back out post-processing there has always been an audible delay.

Granted, this was in windows, but from what I understand there is always going to be some audible processing delay with a USB 2.0 interface.

3.9ms measured audio latency using a loopback cable.

https://rerdavies.github.io/pipedal/AudioLatency.html

Wow, what fx are you running -- and does that or could that include convoluted reverb?

(Convoluted reverb is utterly awesome but more processor intensive than almost anything else)

Edit: and sorry, to be helpful, by low latency, could you meantion how many ms that is -- because while I'm very happy for you, and really interested, 15ms is very different to say 5ms or lower

My normal chain is a noise gate, followed by a comp, a little emulated tube drive, an SVT amp model, an impulse response modeled cab simulator (of course running a 8x12 SVT cab), a plate reverb, and a limiter. I've got some crazier ones, but as a beginner bassist, that's all I really need. There are literally hundreds of effects to choose from though.

Convolution reverb is an option, but it ended up being a little more than the Pi4 could handle iirc. I didn't tinker with it much though.

Latency is under 10ms, I'd have to go back and check my settings to confirm exactly though.

Just double checked my jack settings; I'm running my interface at 48000hz with a buffer size of 128 and 2 periods for a theoretical latency of 5.33ms. I'm sure USB adds a fraction of a millisecond as well.

Thanks! Musically that's really viable and fun setup

A really helpful data point :)

You're doing great! You don't need my help, but just share my own path, because it's fun :)

Yeah, play the bass, if i start talking about computing im not helping...

Err, why am i still here?

I switched to BSD or the OSS driver and went from massive effort ~5ms to zero effort ~2ms

Then I made a two button controller and pedal->usb, and started programming an arbitrary effects controller: a looper + buttons to switch the pedal to control any fx parameter

Fun, but it didn't help me make better music :)

You'll get lower latency with 3 buffers. Try 16/3.

Possible with jackd etc

I switched to BSD and got much better latency on the same hardware

But I think that was the alsa -> BSD oss driver swap, which is possible on linux too. I had just never tried it, since I assumed linux was best

(I'm only sharing this cus i think its interesting, and may help you get good latency)

BSD has in-kernel audio mixing, IIRC.

I'm enjoying the downvotes :)

Was anything I said wrong?

Seriously, I've spent a long time fixing up low latency audio

jackd + OSS on whatever OS u like is not bad advice fyi

I honestly have no idea.

Personally I'm very happy to see that info as I do use both Linux and *BSD and wouldn't have ever tried setting up BSD for audio until now.

I've begun tinkering with GhostBSD lately just to learn more about BSD. Pleasantly surprised to find a lot of familiar linux audio tools were ported or can be easily made to work. Also happy that my ancient Presonus AudioboxUSB works fine in BSD. So much so that I get less random audio glitches than I do under windows 10.

Jack offers the low latency necessary for music production.

Pipewire is supposed to offer low latency as well - at least lower than Pulseaudio, but I don't know how much.

Pipewire runs neck-and-neck with Jack and Alsa. The benchmark pretty regularly; and the difference is +/- nothing. Pulseaudio isn't appropriate for this application.

The RTAudio tools this is based on allows different backends to be configured. I guess you could use Alsa or Jack if you want...

https://github.com/thestk/rtaudio/blob/master/install.txt

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.

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