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10.4.3. JACK Output Configuration

It is possible to configure FluidSynth to output synthesized audio either to JACK or to ALSA. The default, and recommended, method is to output synthesized audio to JACK. This allows the greatest control over audio quality, and the greatest flexibility in terms of routing and multiplexing (for definition see Section 1.4.7, “Routing and Multiplexing”), which allows you to simultaneously record the synthesized audio signal and listen to it.
If you are having problems, you may wish to confirm that Qsynth is configured correctly to use JACK.
  1. Open Qsynth's "Setup" window.
  2. Select the 'Audio' tab, and ensure that "Audio Driver" is set to "jack".
  3. You should also ensure that the other settings are correct - especially that the "sample rate" is set to the same sample rate as JACK (through QjackCtl).
  4. The default settings for most things should work. If you changed a default setting, they are these:
    • Buffer Size: 1024
    • Buffer Count: 2
    • Audio Channels: 1
    • Audio Groups: 1
    • Polyphony: 256
If you are having problems with audio cut-outs, you may wish to increase the buffer settings. The size should be increased in multiples of 1024, and the buffer count should not be increased much. The default setting or one "Audio Channel" provides stereo output, and each additional channel produces another set of stereo outputs. Increasing the "polyphony" setting will allow a higher number of simultaneous notes ("MIDI events," really), which will be useful in exteremely complex situations.