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All channels on DAC 8x ending up on first minijack

LOVE Synthesizers

November 20, 2024 17:31

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Hi

My DAC 8x is detected just fine and I've tried using it both when removing the suggested lines from /boot/config.txt and setting noaudio on the vc4-kms and also leaving those in.  neither has an effect, but I actually would like the HDMI to still be accessible for what I'm doing, as I wish to switch between different devices.

I am then using SDL2, SDL_Audio API in C++ to send sample data to the DAC, and again this works fine (apart from the problem I will describe shortly) and I can switch between HDMI and the DAC 8x and everything.

The problem is that when I define an AudioSpec with 8 channels, I get back that it is fine to use 8 channels and through my callback function I fill 8 channels and they sound excellent, only all the sound gets mixed together and sent through the first audio mini-jack port and nothing ever comes out of the other three.  So rather than 8 different channels I get 4 sounds mixed into each of the two first L/R channels.

Is there a setting I can use to make sure the 8 channels will actually be routed to the 4 different L/R channels of the DAC 8x?

I have made ~/.asoundrc and /etc/asound.conf files and defined both simple and more complex versions of pcm.!default, etc.

I'm not sure exactly how pulseaudio is coming between my program and ALSA and whether the ALSA configuration changes that I make are actually ever happening or overwritten by other configurations from ALSA or PulseAudio, etc.

This post seemed promising: https://support.hifiberry.com/hc/en-us/community/posts/18621370377501-DAC-8X-4x-stereo-ALSA-config
But it didn't work yet.  Also whenever I put something in ~/.asoundrc that file simply disappears on reboot, but putting it in /etc/asound.conf also didn't work, whether or not I disables the HDMI source and the original driver.

All the best,
Kári Halldórsson
LOVE Synthesizers

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3 comments

• 0
  
  HiFiBerry team November 21, 2024 06:43

  This has nothing to do with the ALSA configuration. There is no automatic downmix in ALSA from 8 to 2 channels - except you did some crazy channel maps by youself. 
  
  Try removing/stopping PulseAudio and similar audio middleware and have you program directly access the hardware device. This helps to figure out if this is causing the problem or the audio library.
  
  BTW: The topic you have linked is about duplicating the first 2 channels to the other 6. That's probably not what you want to do.

• 0
  
  LOVE Synthesizers November 21, 2024 13:00

  Thank you, that's interesting.  No I have done no mappings and in fact everything was detected automatically from the start.

  The card registers and in "Device Profiles" I can choose "snd_rpi_hifiberry_dac8x" and select between "Stereo Output" and "Pro Audio" but until now this selection has not made a difference.
  I still wonder where these names and profiles are defined and if I could read and/or change those definitions.

   

  BTW: The topic you have linked is about duplicating the first 2 channels to the other 6. That's probably not what you want to do.

  Correct, but it might still have given me any sound at all from the other three jack outputs, which hasn't yet happened.

   

  Try removing/stopping PulseAudio and similar audio middleware and have you program directly access the hardware device. This helps to figure out if this is causing the problem or the audio library.

  Can you tell me how that would be done, and how/where I would then define Device Profiles that would be detectable?  When I run pipewire or pipewire-pulse I always get "Resource temporarily unavailable" or "Address already in use".

   

  I am going to try a couple more things and see if I can use aplay or pipewire or something similar to send audio to all the outputs.  Are there any examples available for the DAC 8x?  Something like "Download this file and then run exactly this command with these parameters and you should hear sound from the outputs".

  I am willing to start over with a clean Raspberry Pi OS install for Raspberry Pi 5 and just do exactly the changes needed, but that's probably not necessary.  I just need to hear something from all the outputs so I know if it's maybe SDL_Audio that doesn't properly handle 8 real channels and just interprets the samples as L/R/L/R/L/R/L/R and adds them all to the first 2 channels.  I stress that it is still clearly interleaving the 8 distinct sample streams as it does not sound like the samples are being mixed up, but I distincly hear all 4 sounds playing correctly together from one minijack audio output.

  Thank you again for the answer.  I will update in the next couple of days with either clearer explanations of what I've tried or a solution if I find one.  Any suggestions or just test examples to check if I get sound from all outputs would be helpful :)

  Edited by LOVE Synthesizers November 21, 2024 13:02
• 0
  
  HiFiBerry team November 21, 2024 13:12

  to get a 8-channel output, a simple tool is SoX
  
  play -n synth sine 100 sine 200 sine 300 sine 400 sine 500 sine 600 sine 700 sine 800
  
  will output 8 different sine waves on 8 channels.
  
  I don't know what "Device profile" you're refering to. On the lowest level (ALSA), there are no device profiles. It's simple a card with 8 channels.
  
  Audio middlewire like Pipewire, Pulseaudio, Jack and similar tools all do some kind of processing. While these are necessary to allow multiple programs, sometimes even multiple users to access the same sound card, they complicate things. 
  Try to configure your application to directly connect to the hardware device "hw:0,0". If it can't connect something else (e.g. an audio middleware) is already using the sound interface.