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    # Frequently Asked Questions
    
    <!-- TOC -->
    
    - [Frequently Asked Questions](#frequently-asked-questions)
    
        - [Which Audio Interface / Soundcard is compatible with Aura?](#which-audio-interface--soundcard-is-compatible-with-aura)
        - [ALSA Settings](#alsa-settings)
            - [In the Liquidsoap Logs I get 'Error when starting output output_lineout_0: Failure("Error while setting open_pcm: Device or resource busy")!'. What does it mean?](#in-the-liquidsoap-logs-i-get-error-when-starting-output-output_lineout_0-failureerror-while-setting-open_pcm-device-or-resource-busy-what-does-it-mean)
            - [How can I find the audio device IDs, required for settings in engine.ini?](#how-can-i-find-the-audio-device-ids-required-for-settings-in-engineini)
    
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        - [I have issues with starting the Engine](#i-have-issues-with-starting-the-engine)
    
        - [I have issues during some Engine play-out](#i-have-issues-during-some-engine-play-out)
    
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        - [Read More](#read-more)
    
    <!-- /TOC -->
    
    
    ## Which Audio Interface / Soundcard is compatible with Aura?
    
    Basically any audio device which is supported by Linux Debian/Ubuntu and has ALSA drivers.
    Engine has been tested with following audio interfaces:
    
    - ASUS Xonar DGX,
    - Roland Duo-Capture Ex
    - Onboard Soundcard (HDA Intel ALC262)
    - Native Instruments Komplete Audio 6
    
    ## ALSA Settings
    
    ### In the Liquidsoap Logs I get 'Error when starting output output_lineout_0: Failure("Error while setting open_pcm: Device or resource busy")!'. What does it mean?
    
    You probably have set a wrong or occupied device ID.
    
    
    ### How can I find the audio device IDs, required for settings in engine.ini?
    
    * **ALSA**: You can get the device numbers or IDs by executing:
    
        cat /proc/asound/cards
    
    * **Pulse Audio**: You might not need this for Pulse Audio, but still, to see all available devices use:
    
        pactl list
    
    **If you cannot find correct ALSA settings**  
    Well, this is - at least for me - a hard one. I could not manage to find correct ALSA settings for the above mentioned soundcards. The best experience i had with the ASUS Xonar DGX, but still very problematic (especially the first couple of minutes after starting liquidsoap). Since i enabled JACK support i only use that. It is also a bit of trial and error, but works pretty much out of the box.
    
    **If you experience 'hangs' or other artefacts on the output signal**
    
     * Reduce the quality (especially, when hangs are on the stream) or
     * Check the logs (especially the Liquidsoap logs) for any configuration issues
     * Check ther performance of your computer or audio hardware
     * Install the realtime kernel with
    
       ```bash
       apt install linux-image-rt-amd64
       reboot
       ```
    
    
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    ## I have issues with starting the Engine
    
    
    **Cannot connect to socketpath /opt/aura/engine/src/liquidsoap/engine.sock. Reason: [Errno 111] Connection refused**
    
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    - This indicates some issue with the proper startup of Liquidsoap or any related audio device. Check the Liquidsoap logs for details.
    
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    **[clock.wallclock_alsa:2] Error when starting output lineout: Failure("Error while setting open_pcm: No such file or directory")!**
    
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    - This might indicate some issue with your ALSA device. Check if `aplay -l` and `aplay -L` returns some valid device(s). You can also try `alsamixer`.
    - It might be also helpful to set your default audio device in `/etc/asound.conf`.
    - Also check if your user (è.g. `engineuser`) belongs to the group `audio`.
    - Check the audio interface configuration section in `engine.ini`. Verify if the default settings `input_device_0="hw:0"` and `output_device_0="hw:0"` are valid device IDs.
    
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    ## I have issues during some Engine play-out
    
    **Some stuttering sound is hearable. The logs say "strange error flushing buffer ..."**
    
    - Check your Icecast connection. Is it up and running?
    - Maybe there is some authentication issue or an Icecast limitation of max clients. See https://github.com/savonet/liquidsoap/issues/524.
    
    
    
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    ## Read More
    
    - [Overview](/README.md)
    - [Installation for Development](installation-development.md)
    - [Installation for Production](installation-production.md)
    - [Running with Docker](running-docker.md)
    - [Setup the Audio Store](docs/setup-audio-store.md)
    - [Developer Guide](developer-guide.md)
    - [Engine Features](engine-features.md)
    
    - [Frequently Asked Questions (FAQ)](docs/frequently-asked-questions.md)