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Qsynth channel separation

Hi Rui,

I've managed to get qsynth to play piano and violin from two separate engines, in two separate tracks in qtractor. But when I select the piano track, it plays the violin with it and vice versa. I had a separate midi bus for each track going out of it's own audio bus (ie, midi input 'piano' audio output 'piano') to no avail.

Also, is there a way to get qjackctl looking like the attached screenshot - the version I have looks more like Carla which I find confusing . . . . I like the left/right panels and list setting . . . looks more like qtractor which is far more comprehensive to a simple man like me . . .



Image icon IMG_20230907_062941.jpg202.76 KB

Oh . . . and multi channel outs on qsynth didn't work either . . .

rncbc's picture


qtractor tracks playback simultaneously; selecting or highlighting one track doesn't affect the (simultaneous) output whatsoever; you'll need to "mute" or "solo" tracks to that effect.

qjackctl Connections are accessible through the right-click menu or you may switch off for it on Setup > Misc > Buttons > Replace Connections with Graph button.

if you have just one instrument per engine why do you need multi-channel outs ? this is only applicable when you have several instruments or presets mapped to each channel, on the same synth engine; in that case and when properly setup, there will be a pair of audio (stereo) output ports for each one of the 16 possible channels (ie. multi-channel outputs).


Wow, that was quick . . . thanks.

When I said playback was simultaneous I meant that my piano track will playback like a piano AND a violin. And my violin track will playback like a violin AND a piano.

Fantastic about the qjackctl connections button . . . thanks a million. As for multi channels, I did that in the hope of separation, I was figuring that the qsynth was sending the piano and violin through the same channel output . . . so really, I need to suss out how to achieve the same separates in qtractor that I get when using fluidsynth as a dssi plugin - which is stable and works amazingly; just crashes when I try to go beyond 16 channels . . . hence why I was looking at qsynth.....

rncbc's picture

better review your calculations though, MIDI (v1 at least) only does 16 channels per port/device; anything beyond that is pure nonsense (or just "undefined behavior" in some instances;))


So let's suppose there's a violin on channel 40 in a qsynth sound font, how would I get a track in qtractor to play it if the track properties only allows up to 16?

rncbc's picture

qsynth (or fluidsynth for that matter) only allows the mapping over 16 channels, tops; and may I ask where did that supposition come from? :)

let's be clear about this: one soundfont (sf2) may well provide hundreds of instrument presets, sure, BUT you may only have a maximum of 16 (sixteen) channels, each mapped to one, and only one of those presets; iow. one qsynth/fluidsynth engine can only render a maximum of 16 instrument/channels simultaneously, at any one given time and instance.

fwiw. and again, the MIDIv1 limit is 16 channels per device (or port); if we were already on MIDIv2 full-support (and we're not) it would possibly allow for 255 channels, but we're far from there yet, and wonder if we'll ever need it ever soon ;)


I thought that the point of multiple engines in qsynth was to augment the amount of channels . . . albeit in multiples of 16.

Just so we're not talking at cross purposes, let's suppose I have a project that requires only ONE channel - a solo violin. Would it be possible to play the violin listed as channel 40 in qsynth, or does the channel number make it off limits?

rncbc's picture


what part did you not understand of the 16 channels maximum (per device, engine or port)?

but you're right about the multiple engines as means to have multiple sets of 16 channels each; each fluidsynth engine makes up a MIDI device input port, so that each engine may only accept a maximum of 16 MIDI channels, always numbered and addressed from channel 1 through channel 16, an nothing else; no MIDI(v1) device, engine or port may ever have a channel number 40. ever.

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