Multitrack audio interface - use channels for independent programs

Hey :slight_smile:
I have a question regarding multitrack interfaces.
It’s not actually related to Ardour, but i figured, that many people here have some experience with multitrack audio on linux. I run darkice, an icecast2 broadcaster, on a raspberry pi.
I want to have 2 streams with independent sources. Darkice addresses the interfaces with plughw. I thought about getting a 4 channel interface. Would I be able to set them up, that one darkice instance gets channel 1-2 and the second gets channel 3-4? That would speed up the setup immense.
For now, I can run two Behringer UMC202HD, and it works just fine. But my actual plan is to build a DIY-Interface, that attaches to the Pi with some additional features and back-side XLR and gets the signal directly from our A&H SQ5. And since 2 I2S-sources on one PI can get problematic, I’d like to stick with only one I2S-Interface.
My main concern now is, that I don’t want to spend money on a 4 channel interface to test the setup without the slight hope, that the project will be possible at least.

Uh, you’re really doing this the hard way. Just plug the rear-panel USB connector from the AllenHeath SQ5 into the RPi and you have yourself a 32x32 channel USB CoreAudio interface.

That would be an option, but unluckily the SQ series only is able to address one USB at the time. And I’d like to have the option available to record multitrack on a USB drive.
Our current setup in our church is:

  • the SQ5, multitrack on a USB drive enabled so that we can record multitrack audio if need be. E.g. on quartett hymns or orchestra, I want to have multitrack as a backup in case the mix on the stereo recording is bad. I don’t want to have it for the regular service. I’m not used to multitrack editing yet and actually I’m not the operator. Also, the recording folders would explode, if we record the two services during a week. That’s 3-4 hours of 14 channel multitrack :slight_smile:
    We have a guy sitting at the mixing station, and he is able to get the mix perfectly fine for our live recordings for the archive and livestream.
  • the stereo recording is done via a Steinberg CI2+. This is done due to the limitations of the USB outputs. I’d love to have Wavelab hooked up directly via USB, but then the multitrack backup wouldn’t be possible. And yes I know, this is a not optimal solution.
  • the 2 streams run from 2 UMC202HD.

If I’m able to hook up a 4 or 8 channel interface to the Raspberry PI and use the channels on independent programs, than I would love to run the 2 streams from this one interface.
The planned Pi hat will get some levelmeters, status leds and hardware control buttons for the stream. If that’s done, I want to expand it with a 4, 6 or 8 channel ADC directly on the hat, so that I can run the streams and the stereo recording from this Pi, while the USB drive would remain for multitrack backup.
In that fashion we should be able to completely run the service headless. No disturbing monitors, etc.
It would basically become a fully enclosed stream- and recordingbox.

This might seem a bit overkill, but I am currently training to change my career path from a mechatronics technician to software development, and electronic devices are my hobby. That’s why I’d love to get it done. It would be a great starting point to my portfolio. It’s actually the first project from my to-do-list, that I start, and I know, that it would be a good solution for other small churches/communities like ours.
I have some other projects waiting in the pipeline, but they can wait for this one :slight_smile:

Use jack. You may need some extra plugins to make a jack interface appear as an alsa device if you don’t have pulse also running. The latest thing would be pipewire which is designed to take the place of pulseaudio, jack and provide one or more pseudo alsa devices. I do not know if pipewire will work on a pi or not (may on a pi4 which I think is 64bit).

Thanks for the hint :slight_smile:
I’ve found out about jack and pipewire a few days back. I did test a Manjaro distro on a Pi4 4GB and managed to get pipewire running. Via helvum I could route the channels from my UMC202HD independent. So, I should be able to route them to two darkice-instances (If I get darkice to run on Manjaro). That allows me to use only one 4-channel interface for two streams.
Plan for tomorrow is to get darkice up and running. Also, I want to try out asterisk with music-on-hold accessing the interface via pipewire, so that I can have a number to dial for the absolute non-technical older people. Icecast will run on the same pi. A simple website with the players will be hosted on the Pi itself. That should be enough, as our services don’t get accessed from hundreds or thousands of people. If the bandwidth at the location isn’t good enough (here in Germany, that’s absolutely possible, we pay premium prices for crappy internet :frowning: ) or the church expects too many listeners, an external Icecast- and webserver would be needed.

I also tried out pipewire with USB hooked up to our SQ5. I can see all Multitrack outputs in helvum. If the performance of a Pi3 or 4 is good enough in headless mode with a light distro, I could use it to run directly from the SQ5.
The 2 Stream-groups are taken directly to darkice, the stereo-recording can be done using that. While the stereo recording runs for the complete service nonstop, I could try to capture multitrack per button press for single hymns. If it doesn’t lead to quality issues (stuttering, losing data during start/stop of the multitrack recording), that would allow me to get rid of all interfaces and empty the desk completely :slight_smile:
No more desktop-PC for recording or streaming at all. The recorded files can be accessed via samba-share in my private network or backup every night on my OMV-server.

I will make four versions of the setup.

  1. Pi with hardware controls for
  • two streams
  • an asterisk-server
  • stereo/multitrack-recording, accessing the digital mixer or an external audio-interface via USB
  1. Pi with hardware controls for two streams, an asterisk-server, stereo-recording and a built-in 6-channel ADC for analog setups.
  2. Same as 1, but with a touch-monitor, no hardware control and a self-coded app.
  3. Same as 2, but with touch-monitor.

When I get to figure out everything (hopefully tomorrow morning), I have all puzzle pieces together to finalize the first prototype.
It will be a test-setup ready for another church with version 3. Not our church first, because our system is already running, while they don’t have a stream-setup yet. And their sys-admin doesn’t know anything about linux.
Should be done by Christmas, at least I hope so. Version 1 will be the next step for our own church. Version 2 and 4 with the built-in ADC will take the most time I guess.

That was quite a wall of text, but I hope, someone finds it interesting. I know, that this is not the best forum for this topic, but I thought, after starting the conversation here and actually getting answers, I might as well tell you about my progress :slight_smile:
Thanks for your help!

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