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I want to play a metronome audio tick out of the built-in headphone port, while playing an audio stream out of a USB soundcard. How can I do this?


Deeper context:

JACK is running the USB soundcard, and Pulseaudio is probably the thing that is in charge of the built-in soundcard*.

My first thought is to use both JACK and Pulseaudio in tandem, using the JACK sink for pulseaudio input. Routing the metronome to the Pulseaudio JACK source makes the JACK source appear in pavucontrol under the 'Input Devices' tab - the mixer shows it is receiving the metronome signal. But no matter what I do I can't get this to actually be output by pulseaudio at any point.

How can I send the signal from JACK source to the built-in headphone port while still using the USB soundcard?


(* Tested this by using the 'Test Sound' function in Linux Mint's Sound manager - plays a test tone happily out of the headphones, which suggests this should be possible!)


Edit: fix typo

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  • You don't seem to be running Pulseaudio at all (you can check with ps axu) I suggest to remove the pulseaudio tag.
    – dirkt
    Commented Mar 20, 2017 at 13:33
  • Good point - though originally I thought that it was a pulseaudio problem. Better to leave it in to be helpful to people in a similar situation or remove it for correctness?
    – theo-brown
    Commented Mar 25, 2017 at 23:12

1 Answer 1

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Fixed it!

Solution: using the alsa_out module.

To use them, you start JACK as normal. Then you start an instance of alsa_in or alsa_out for each additional device (and “direction”) that you want to use. alsa_out will create a set of ports representing the playback capabilities of the device, and alsa_in will represent the capture/recording capabilities

So:

  1. arecord --list-devices to find name of built-in soundcard (hw:0,0)
  2. alsa_out -d hw:0,0 to create the alsa_out ports that now appear in jack
  3. Connect up metronome to alsa_out port in JACK - now plays metronome out of headphone socket and any other audio desired out of USB soundcard!

http://www.jackaudio.org/faq/multiple_devices.html

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  • When doing step 2, it prints Capture open error: Device or resource busy for me. What is occupying it? Commented Nov 30, 2022 at 15:24

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