how to bypass audio processing in fedora 27?

asked 2018-02-14 04:16:48 -0600

billwilliams gravatar image

updated 2018-02-14 04:17:20 -0600

Hi,

There are discussion on various forums about how to get Linux apps to pass through PCM to the USB output without any secondary processing by alsa, pulseaudio, etc. I cannot understand how to do this with Fedora 27.

If I go to the gnome options and select sound, I can see a choice of audio devices. The device I want is in the list and it has both analog and digital (iec958) options. If I select either of these two options for the device, I can get music to play on external devices (two different USB DACs). But it seems to me there are a few problems here.

  1. I cannot understand how analog audio is sent over USB. Does this make any sense?
  2. It seems that alsa or pulse or some other piece of software are involved and possibly changing the sampling rate of the PCM decoded by the music player (aplay, vlc, mplayer etc.) and the DAC does not indicate that I am getting the full sampling rate of the file as indicated by the file command and the music player output.
  3. I have a small number of DSD files and it appears they are decoded to PCM rather than being output correctly as DSD.

Can anybody please explain the best way to send music over USB to a USB DAC without any additional processing?

Thanks!

Bill

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Comments

I just finished building deadbeef from source. This outta be in somebody's repo! Works quite beautifully and enabled me to turn off whoever (the music player itself, or alsa, I don't know) is doing the resampling.

So now Linux and deadbeef and one of my USB DACs are getting along well. The other DAC still doesn't show any signs of what signal it's getting.

billwilliams gravatar imagebillwilliams ( 2018-02-14 12:08:36 -0600 )edit

@billwilliams Not sure it has to be Fedora27 in your case but you could take a look at Volumio OS, which of course could run in a VM oon your Fedora.

btw, dnf copr search deadbeef returns a couple of results - though haven't look at what they actually are.

florian gravatar imageflorian ( 2018-02-14 12:28:56 -0600 )edit

Hi Florian. I saw copr but I am new to Fedora so I don't know which repos are trustworthy. And it looked like he didn't have an update since F25. Since it wasn't something I heard of before I just built it from source. It should be in rpmfusion. It's really a good app.

Yes I realize it's not fedora specific but that's what I run so I figured to mention it along with the problem description.

What is copr and is it approved by the fedora project? Thanks for all your help :) Bill

billwilliams gravatar imagebillwilliams ( 2018-02-14 13:23:05 -0600 )edit

COPR is just a build system for personal repositories/packages that can be used for anyone for anything. So, trustworthiness is not clear. Packages are not reviewed by Fedora, though you can always browse and review the sources yourself (often not an option).

florian gravatar imageflorian ( 2018-02-15 09:49:53 -0600 )edit
1

I guess it might be OK to convert your first comment to an answer. :) Update: However, it seems that deadbeef is also using Alsa/PulseAudio. So, what makes it special compared to other players?!

hedayat gravatar imagehedayat ( 2018-02-26 12:32:36 -0600 )edit