Digital Larry
Posts: 75
Joined: Tue Jul 24, 2012 9:10 pm
Location: Silicon Valley, CA

Eliminating pops/crackles in USB audio with JACK and SooperLooper

Sun Dec 01, 2019 3:43 pm

I have a Pi 3 Model B 1.2 mounted in one of those 7" LCD touchscreen cases.

I have modified the GUI code for SooperLooper http://essej.net/sooperlooper/ to hide some of the features which I never use and make it possible to display 3 looping tracks on the LCD. This is all working quite well. I am using a Macmillen Softstep MIDI footswitch to control SooperLooper and JACK to connect everything audio/MIDI. At the moment I'm using qjackctl but I'm going to see if I can get Claudia working on the Pi because that will remake your audio connections automatically which is a huge time saver for development.

The audio interface is a Behringer UMC-404 4-channel in/out USB box. I'm only using 2 channels at the moment to put this in the stereo effects loop of my Eleven Rack guitar preamp.

Like I said, it all works great except for pops and clicks at random times in the audio.

https://wiki.linuxaudio.org/wiki/raspberrypi

I looked at some tips on optimizing audio on the Pi, and some of the things I am not going to be able to do. For example:
- I really need the GUI, even though SooperLooper can run headless, if I were going to do that I'd just buy a pedal
- I really need this to be on the LAN so I can share and transfer files over to my PC. Whether Ethernet or wireless, each is possible but I've heard bad things about Ethernet. Currently I'm using Wi Fi and either SSH or occasionally VNC to drive the Pi from another computer. As far as file sharing goes I am planning on installing Samba so I can access it from my Windows machine.

I am going to go through that Wiki link carefully, but on the off chance someone reading this has already gone down this path, it would be great to hear from you!
Pi user since 2012. Python, Pygame
Support, remot3.it, Inc.

renice123
Posts: 224
Joined: Tue Oct 15, 2019 3:56 pm

Re: Eliminating pops/crackles in USB audio with JACK and SooperLooper

Sun Dec 01, 2019 5:42 pm

My jack was noisy when I changed the processor power settings. This surprised me, because a drop in processor speed from 1400 MHz to 1200 MHz should not have such an effect. I sin that I used pulseaudio to communicate with jack. I gave up pulseaudio because I could not overcome the quiet unpleasant rustles and crackles when working together with ALSA and Jack.
I physically deleted pulseaudio and now everything is fine, but for now I have stopped experimenting with lowering the processor power.
I also “moved” the Jack & ALSA server to a separate Raspberry mini-computer, I transmit sound over the network and also works very well.
Perhaps you are using pulseaudio (this program can hide deep in the OS and run randomly)?
There is another reason why rustling and noise can occur - a bad driver for a sound card. I use a DJ sound card (with pass-through channels), and I could not start it with the proper quality on the Buster - the driver does not work well. Jessie is doing well.

sudo apt-get remove pulseaudio =)

Digital Larry
Posts: 75
Joined: Tue Jul 24, 2012 9:10 pm
Location: Silicon Valley, CA

Re: Eliminating pops/crackles in USB audio with JACK and SooperLooper

Sun Dec 01, 2019 7:12 pm

Thanks. pulseaudio wasn't installed. I did install Samba so I could easily transfer or access the recorded WAV files from my Windows machine. Seems like at least some of the crackles are in the recorded WAV files.
Pi user since 2012. Python, Pygame
Support, remot3.it, Inc.

Return to “Graphics, sound and multimedia”