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Weird Midi controller problem


first I want to say thanks for qtractor, it seems just to be made for my workflow. I found instrument definition files for both of my keyboards and imported them successfully. The template creation is perfect for my different setups. Visiting a home recording workshop showed that everything I need is possible with qtractor, too. Today I tried to use qtractor with controller functions:

My Workstation allows me to use 8 trigger pads and i assigned them to control the transport. Every function (forward, fast forward, backward etc.) works fine, but play/pause does not.

The problem is that sometimes it works and then several times in a row, but most of the time (90%) the playhead moves a little bit and then jumps back, stopping. Holding the button plays the project as long as the pad is pressed.

- Switching to another trigger pad does not work, same problem
- Switching to a key from the keyboard works!?
- Hitting the space bar works as always

Midi sniffing shows that the trigger pad sends note on/note off as the key does, but the pad has no velocity (only 127 and 0)

As I said, every other transport function works using the trigger pads, so I am a little desperated :-) Has anyone assigned the play/pause function to a midi controller (not a key)? Can anyone confirm this behavior or is my workstation to blame?


rncbc's picture

have you check whether Transport > Continue Past End is playing you tricks?


Hi Rui,

thanks for the quick reply, I tried:
- Turning off "Continue past end"
- Deactivating a2jmidid
- Turning off "Auto backward"
The latter moved the playhead without setting it backward, which is IMHO the desired behavior.
If nobody else has this problem, I put the blame on my workstation and use the space bar to play/pause.

Could you please explain the "Latch" option when assigning midi shortcuts, I did not find it in the documentation?

Thanks for your help


rncbc's picture

Could you please explain the "Latch" option when assigning midi shortcuts, I did not find it in the documentation?

the "Latch" option is only applicable to on/off toggle subjects and relates to "latch" vs. "momentary" (opposite) modes of switches--latch=OFF is same as momentary=ON and vice versa--and applies mostly to foot-switches (or pedal controllers) mode of operation.

latch (=on) mode is the default setting for most controllers, but when you have a midi controller that operates in "momentary" mode, it usually sends an event when you press (0->1) and another one when you depress (1->0)--that's why it is said "momentary": the switch state is only signaled momentarily on while you keep the switch pressed, returning to its former state when you depress it.

setting the "Latch" option to OFF for these later cases, will simulate a toggle switch, meaning that the target subject state will only change to ON _or_ OFF when the switch is _either_ being pressed _or_ depressed, respectively.


Hi Rui,

I've added the Latch info to the wiki (just above this section), but I never use the MIDI Controller features so don't really understand them. It seems, though, that questions on controllers crop up from time to time and there are other options which aren't explained in the wiki - Logarithmic, Feedback and Invert (I'd already put "Hook" in, with info from a previous post) - so it'd probably be good to add these too. If you'd like them adding, could you give me a quick overview of their functions please? And if you could have a scan of the info that's already there to make sure it's OK, that'd be great.

There's no rush for this, of course, but if you get the chance I'll finish off this section of the wiki, putting all the options in bullet points. That should hopefully head off further questions.

rncbc's picture

hi Yuba, thanks again and always for your efforts on updating the Wiki

in summary:

  • Logarithmic - the linear scale of the MIDI controller (rotary knobs, sliders, etc.) is mapped to a logarithmic scale value on the target controlled subject, usually applicable to audio volume, dB scales or even frequency spectrum ranges;
  • Invert - the minimum-maximum range of the MIDI controller are inversely mapped to the maximum-minimum scale values on the target controlled subject (and vice-versa);
  • Feedback - makes any change on state value of the controlled subject to be sent/feed-back to the MIDI controller, to let the latter reflect and sync its state accordingly; most applicable to MIDI controllers with visual (LEDs) and/or mechanical feedback (eg. motorized faders);
  • Hook - the MIDI controller and its controlled subject state/value are always in sync (hooked to each other); otherwise a deferred sync mode is in effect, with both ends playing catch-up on each other's from either direction, until they match their states/values;
  • Latch - the opposite of momentary control (already explained in the other comment);


Thanks very much. Have added your info and the whole thing looks much better now. That was very educational :-)

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