Enhanced AUX Sends

Submitted by bluebell on
Forums
Qtractor

A track has as much audio channels as its destination bus. The mapping is straight forward, alsways counting from the beginning.

So if there is a track with a multi channel plugin, e.g. drumgizmo, and we use an AUX send to a 2 stereo bus then the first 2 channels are sent to the bus. To send channels 3+4 to the stereo bus we have to use a matrix mixer plugin. To distribute channel 1+2 to a stereo bus, 3+4 to another, 5+6 to another there will be a big mess with many instances of a matrix mixer plugin.

Is it possible to enhance AUX sends by making it controllable which channels in what order are sent to a bus? This would make the use of multichannel instrument plugins much easier, also sidechain handling.

Submitted by G3N-es on Mon, 23 Jun 2025 - 14:10

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Something like generating a list with the number of available channels. "Channel number" to "a numeric box with available channels, including 0, in case you want to mute that channel."
By default, it would appear associated with its channel.

Channels:
1 to Channel [ 1 <>]
2 to Channel [ 2 <>]
3 to Channel [ 3 <>]
4 to Channel [ 4 <>]

For typical sidechain use...
Channels:
1 to Channel [ 3 <>]
2 to Channel [ 4 <>]
3 to Channel [ 0 <>]
4 to Channel [ 0 <>]

We know we can achieve the same thing by adding a Carla 16 plugin in front... and adding another one in back to correct the flow... but this would simplify things enormously.

As always, I don't know the complexity of the issue... but it would certainly be very useful.

Rui will tell us.

Submitted by rncbc on Mon, 23 Jun 2025 - 14:50

Permalink

interesting thought...

an Aux Send would target multiple buses? oh no--the least what it might do is to select which channel go to which channel on the target (single) bus, on a 1:1 mapping... and nothing more than that.

I'll think about it ;)

cheers

It's only the channels that we want to assign, e.g. an AUX send that sends channel 1+2 of a standard stereo track to channels 3+4 of a 4-channel-bus. Or channel 3+4 of a 4-channel-track to channel 1+2 of a standard stereo bus.

For sending audio to multiple buses we would insert multiple AUX sends.

Submitted by rncbc on Thu, 26 Jun 2025 - 16:10

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wait a minute,

where did you get the idea that an audio aux-send may ever be set to an audio output bus with a different channel count than the current track or bus?

are you using a modified hack build or something? or is it just a thought experiment?

seeya

Submitted by rncbc on Sat, 28 Jun 2025 - 12:30

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WIP in new [xauxsend] branch...

at least you now can choose audio output buses with disparate number of channels, to start with.

a channel I/O matrix UI editor will come later, soonish ;)

cheers

Submitted by bluebell on Sat, 28 Jun 2025 - 13:23

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Thx Rui.
First tests with an audio track that is connected to a 4 channel bus show:

  • AUX send to a 6 ch bus works fine (the first 4 channels get the signal)
  • AUX send to a 2 ch bus crashes Qtractor as soon play starts and the AUX send is made active

Submitted by bluebell on Sat, 28 Jun 2025 - 16:35

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Crash ist fixed.

When sending the 4ch signal to a 6ch bus then ch 3 gets no signal. Probably due work in progress at the mixing matrix.

Submitted by rncbc on Sun, 29 Jun 2025 - 08:08

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rebased/squashed to v1.5.6.9git.e26ff4 [xauxsend]

ps. remember to just do a
git reset --hard origin/xauxsend
from time to time, to cleanup for the lost refs.

cheers

I made a 4 ch wav where the metronome sound hops from 1 to 2 to 3 to 4.

  • The output meters of the 4ch bus look ok
  • The output meters of the 6ch bus are in wrong order and ch2 gets no signal
  • The output meters of the 2ch bus start with ch2 and ch1 gets no signal
  • The waveform display in the track is wrong
File attachments
Sample session
Real waveform
Qtractor's display of the waveform

Submitted by rncbc on Sun, 29 Jun 2025 - 13:47

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this might well be another issue unrelated to this topic/branch--it probably shows on main and develop, a 4ch wav file weirdly shifting multi-channel graphical waveforms depending on zoom level...

while it sure is a good catch, it should belong to yet another new topic, perhaps.

Submitted by rncbc on Sun, 29 Jun 2025 - 15:13

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it's-alive now in v1.5.6.10git.08c819 [xauxsend]

redo/undo capability remaining to the next sprint, whatever ;)

as always with experimental stuff, please test this with disposable sessions only.
cheers

I'm off work for a couple of days and, surprise... Another powerful feature is working.

@bluebell Well, yes. You'll have to update the wiki. The same thing happened to me with the automation article :) .

I've always found the matrix UI confusing. I know it's a standard in the digital audio world (I suppose inherited from analog connection boxes), but I find a simple "a > b" assignment list like the one I mentioned, or node connections, like the Qtractor connections window, more intuitive.

But I won't complain... welcome.

However, I think it doesn't make sense that the radio button doesn't activate and deactivate when clicked.

I think that should be fixed. Currently, there are two clickable elements: the box and the radio button... and there should be just one that functions as the box.

Maybe replace the two elements with a single button that changes its icon when clicked?

Submitted by bluebell on Sun, 29 Jun 2025 - 16:20

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Works fine.

Loading an old session with AUX sends works ok with the desired default channel mapping.

When it's in the next version I have to mark How To 6 as obsolete.

Submitted by G3N-es on Wed, 2 Jul 2025 - 18:05

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Hi @bluebell
I just realized that my "How to 5" for sidechain needs to be rewritten from scratch.
I think the How tos that replace the current ones should be done when the new version is released and we've had time to thoroughly test it.

How do we avoid repeating ourselves?
I was thinking that maybe 6 (alternative methods) could be done now to explain the workflow with LSP plugins. It could be interesting.

How do you see it? Any other ideas?

Submitted by G3N-es on Wed, 2 Jul 2025 - 21:14

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This way, a history is kept. Plus, keeping them can give ideas for how to approach other workflows.

Then I'll also add explanatory notes to mine when the new one is available.

I just renamed it to [How To - 5 Sidechain Workflow with Carla Plugin] , so it doesn't conflict with your new one.

I've also removed the zip file with the example files (for various reasons) and edited the article accordingly.

One of the reasons is that Qtractor will now have a native way to implement sidechaining. So many references are no longer necessary, as there will be a simpler way to do things, and the method proposed in the article will be outdated.

Thus, the article becomes primarily a generic introduction to the sidechain technique.

Submitted by rncbc on Tue, 1 Jul 2025 - 18:46

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tomorrow, if nobody stands against it... ;)

cheers

ps. if all goes well, xauxsend branch will be squashed into a single commit and deleted afterwards.

It's exciting to see Qtractor grow.

Now, the simplest method if you need a sidechain is to create a dedicated bus for the track you want to work on and host the sidechain plugin on that bus. This also allows you to mix the effect with the original signal from the track's fader, even if the sidechain plugin doesn't have an effect mix control.

Thanks a lot!

I've created a QSS to mitigate the unchecked box issue 😏:

1. Remove the unchecked icon, so the user immediately understands that the place to interact is the box.
2. This is reinforced with a hover effect.
3. If you click on the icon, it flashes, indicating that if you click it, it will stay there.

/* AuxSendIOMatrixForm */
qtractorAuxSendIOMatrixForm QTableWidget::item:hover {
  background: palette(highlight);
}
qtractorAuxSendIOMatrixForm QRadioButton::indicator {
  width: 8px;
  height: 8px;
  margin: 0;
  padding:0;
}
qtractorAuxSendIOMatrixForm QRadioButton::indicator::unchecked {
  background: rgba(0, 0, 0, 0);
}
qtractorAuxSendIOMatrixForm QRadioButton::indicator::checked {
  background: #000000;
}
qtractorAuxSendIOMatrixForm QRadioButton::indicator::checked:pressed {
  background: rgba(0, 0, 0, 125)
}

I'm not going to dwell on this topic, but... I still think we should find a less confusing way to implement it, regardless of where you click on the box.
Click = if active, deactivate; if not, active.

File attachments
qss-matrix.gif

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