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i know there already is a video tutorial by libre music production, but it's for an older setup of qtractor and isn't very clear tbh

anyways, what i want to do is send all of my melodic instruments to a bus and use the calf sidechain compressor to sidechain it to a dedicated signal. what i'm having trouble with is how to route my signal to the plugin. i imagine you have to fiddle with channels and routing, but i'm new to qtractor and would like to learn it although i need help

can anyone help me? thanks!

btw i'm using ubuntu studio 20.10 with the default setup

rncbc's picture

what older setup? as far as I'm concerned all the things in the LMP video may still apply.

if what you want is only have a separate "wet" output then just create an audio output bus where you insert your compressor fx plugin; then insert an aux-send on the track (or bus) you have the source audio content and want to route also to the "wet" bus.

if what you want is to have "sidechain compression" like in the LMP video, remember that it uses the Ducka plugin which takes MIDI for the sidechain command signal and not an audio one like the Calf compressor plugin I think do.

For the latter case, well... it's complicated! :) As you might know from other threads here, is waaay too complicated to explain :)

my stance is still the same: qtractor support for side-chaining scenarios is very, very limited, if not non-existent. sorry.


hey, sorry about the bump, but i discovered you can get a sidechaining effect using a foss plugin called b.shapr; you can find it here:

just put it on a track or bus, open it, set the time setting to one beat and the mode to level, and draw a curve to duck the audio every beat

rncbc's picture

yes but that's not quite "sidechaining" if at all... eh, nevermind :)


autumncheney: thank you for suggesting BShapr (LV2). I was searching for a way to achieve side chaining in Qtractor and your suggestion was the easiest. I just tried that LV2 plugin and it seems to achieve something that sounds like sidechaining.

rncbc: thank you for Qtractor!

I ended figuring out how to use the Calf Sidechain Compressor with Qtractor, and it seems to work great.
I learned from this page:

The problem I have now is when I export the song to a .wav in Qtractor, I can't hear the drum and I can't hear the synth. I can only hear the track that has nothing to do with side chaining. I'm pretty sure it has something to do with the 'Dedicated output' for the track, 'Synth 1' and also the side chaining bus.

Any tips on what I'm doing wrong based on the attached screenshot?
Synth1 is my synth that needs to be ducked, (and it is), and Drum is the signal that causes the ducking to occur.
However, when I export to a .wav, I don't hear all the tracks.

File attachments: 
rncbc's picture


you're not doing nothing wrong: it's just that dedicated insert/send ports won't apply to audio export: only (internal) output buses, sorry. that's by design.

the solution is about "bouncing" ie. recording the desired outputs in real-time.

Hi, thanks for the info and for the bouncing suggestion.

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