Qtractor Wiki How To - 5 Sidechain Workflow with Carla Plugin

How To - Contents

Note: This article is obsolete. Since Qtractor 1.5.7, auxiliary sends allow you to route audio signals from channels through a matrix. Therefore, external plugins are no longer necessary for this task. For example, if you want a sidechain effect in a stereo environment:

1. Create a four-channel SideChain bus that houses the sidechain processing plugin and an auxiliary send to the destination bus in the mix.
2. Send the signal to be processed to channels 1 and 2 of the SideChain bus with an auxiliary send.
3. Send the modifier signal to channels 3 and 4 of the SideChain bus with another auxiliary send.

This will allow you to mix the original signal with the processed signal in a flexible and powerful way. In any case, the article is still useful for understanding what a “sidechain” is, its practical uses, and examples of various workflows.

• Author: G3N-es.

• Difficulty level: Advanced.

• It is assumed that you already know:

  • Configure Jack.
  • Configure Qtractor (plugin paths, etc).
  • Create a project with midi and audio tracks.
  • General notions of mixing and mastering.
  • Configure midi and audio tracks.
  • Load plugins on tracks and buses.
  • Install Plugins.

• You will learn to:

  • Create advanced audio routing.
  • Take advantage of that knowledge to create sidechain flows.

0. Purpose of the tutorial

Have sufficient knowledge to be able to apply different workflows with sendings to sidechains in Qtractor. The workflows proposed here are only a partial reference of infinite possibilities. Related content: How To - 6 Alternative Sidechain Workflow with Aux Sends

Qtractor does not have pre-built workflows. In exchange, it offers you total freedom to create your own workflows.

0.1. Ingredients

• Qtractor 0.9.36 or higher
• Plugins lv2
  • GM Synth
  • Carla- lv2
  • Calf-plugins

0.2. What is a “sidechain”?

Sidechain is a signal sending technique that allows modifying or controlling an audio signal “direct A”, with another audio signal “external B”.

Types of sendings in Qtractor

• Sending to own bus by default
• Sending to track (inserts)
• Sending to auxiliary bus

Plugins with sidechain They are characterized by having more inputs than outputs: Every sidechain plugin must have extra input/s for the sidechain “external B” signal in addition to “direct A” input/s.

“Direct inputs” are the first ones that correspond in number to the outputs. The remaining ones are “entries for sidechain (or external)”. The workflow is conditioned by the demands of each specific plugin (mono, stereo, purpose of the plugin, etc.).

Two very widespread uses:

• Dynamic sound control (compressors, expanders…)
• Vocoder synthesizers.

However, there are no limits, all types of plugins can be developed with a sidechain, where an “external B” signal “automates” a certain parameter or parameters of a plugin in order to control or modify the “direct A” signal. Not all plugins support sidechains, they must have been designed and programmed expressly for this purpose.

0.3. Channel behavior in Qtractor

1. Undefined channels. A bus is not mono, stereo… A bus simply has channels. It is you who, through the interconnections, define the configuration (mono, stereo, soundround… with or without sidechain). The number of channels on a Bus can be modified at any time, although it is advisable to design the project connections and workflow in advance.

3. The buses determine the number of channels in the tracks. Sidechain plugins have extra inputs. So we need extra channels that allow the signal to be directed towards them. Qtractor buses allow you to create these new channels.

4. Although buses (and therefore tracks) with different numbers of channels can coexist, it is not recommended. If you plan to work with sidechain, buses with the same number of channels are the best option. Otherwise, “Auxiliary Sends” will not work and “Inserts” may create conflicts.

5. An audio track will attempt to inject audio to all available channels before entering the plugin chain. This allows you to combine mono and stereo audio files into a single track in an intuitive and simple way. In general it is desirable behavior. It is not in the specific case of side chains. However, it is easily solved with plugins that mute or interrupt channels.

Thanks to the “switch plugin”, we now have the 2nd channel free to be able to carry out sidechain workflows. What at first seemed like a configuration of stereo track, it turned out to be a mono + sidechain channel configuration. I want to emphasize this idea, although the tracks start from a stereo configuration for panning control, a Qtractor Bus gives you undefined channels, so that you define them. And this feature is what we are going to take advantage of to apply sidechain.

6. The “midi instruments” generate an audio signal within the plugin rack. They do not behave like an audio track. They only occupy the bus channels that correspond to their outputs. That is why with them it is not necessary to use switches. channels.

7. Standard sidechain channel configurations:

• Mono: 2 channels (the first for direct, the second sidechain).
• Stereo: 4 channels (first 2 for direct, remaining 2 for sidechain).

1. Send to own bus: Assemble a simple vocoder

Compatible with “Jack (genuine)” and “PipeWire”

It’s the simplest way. There is no need to create new sendings. We take advantage of the signal send from a track to its default bus.

It could be summarized as, whenever we need a sidechain, creating a specific bus for all the tracks involved.

1.1 Connection scheme

1.2 From scheme to practice

EXAMPLE SESSION

• vocoderSynt: MIDI track responsible for providing the tonality (carrier) to the vocoder.
• vocoderVocal: Audio track responsible for providing the voice formant (modulator) to the vocoder.

CONFIGURE BUSES

The first thing we will do is create an exclusive bus for the “vocoder” tracks, where we will host the “Calf Vocoder” plugin.

In the mixer:

1. Double click on the bus Master title to access the buses configuration. (2) Rename it “Vocoder”, (3) in “Channels” assign “4”, (4) uncheck the “Autoconnect” box and finally (5 ) confirm the configuration with “Update”.

Now we will need a new Master channel.

1. Rename it as Master, (2) “Mode” change it to “Output”, activate the box (3) “Autoconnect” and click on (4) “Create”.

It’s Qtractor’s own and unique 2-step (Configure > Save) way of managing “buses”. Therefore feels strange at first. However, once you see the logic, it is more productive than the traditional system (New > Configure > Save).

Adds the “Calf Vocoder” plugin to the “Vocoder” bus.

“Calf Vocoder” has a stereo sound concept, and arranges the channels as follows:

• The first two (direct signal): are for the Carrier, in charge of providing the tone.
• The remaining two (sidechain signal): are for the Modulator, responsible for providing the formant (which allows it to be perceived as a vocal timbre instrument).

Adds an “Aux Send” to the “Master” bus.

SET TRACKS

Track vocoderSynt:

1. Right click on the plugins box of the midi track “vocoderSynt”.

2. Assign as audio output bus: audio > Vocoder.

3. To set the timbre of “General Midi Synth”, go to the track properties (in the mixer, double clip over the track title). Select “General Midi Synth”. Establish a bank and program of your preference.

“General Midi Synth” can be deconfigured by playing “Piano default” instead of the program assigned by you. If this happens, reassign the bank and program. It is not very common, but it can happen.

Track VocoderVocal:

1. Double click on the title of the audio track “VocoderVocal”. Assigns the “Vocoder” audio bus as output.

2. Add the plugin “Carla-Patchbay (16chan)” connecting only channels 3 and 4 intended for the modulator. We are going to use it as a switch plugin. It may seem that using Carla for this purpose is killing mosquitoes with cannon fire, however I have not found another that does the job better.

We already have all our connections!!!

Try and experiment with different settings on the Calf Vocodorer and with different timbres on the carrier.

2. Send to track (inserts): Side compression

“PipeWire” Compatible: Tested in version 0.3.84.

“Jack (genuine)” Personally I haven’t had any problems. However, some users comment on the following incidents: * Inserts may not send audio. * Inserts may stop working when you reopen the session.

WARNING: Qtractor never had a tool for send to track. Using Inserts for this purpose is discouraged; they were not designed for this. However, at the time this tutorial was written, it was the only way to accomplish this task. Today, we have plugins that efficiently make sends to tracks. We recommend the LSP “Send” and “Return” plugins, hosted on the “Carla-Patchbay (16chan)” plugin, to reliably recreate this section of the tutorial. More information at How To - 13 Make Successful Audio Connections

2.1 Connection scheme

2.2 From scheme to practice

This time we will add the plugins from the sequencer instead of the mixer. The reason is simply educational, to see the many options that the Qtractor UI offers.

We will add a Sidechain Compressor to the track “brightness” (intended for accompaniment). The intention is to lose presence (volume) when the Vocoder (lead voice) plays. This way we will achieve a cleaner mixture.

1. We added the plugin “Calf Sidechain Compressor” in the track “brightness”.

2. We added an “Insert” audio on the midi track “vocoderSynth”.

3. We added an “Insert” audio on the midi track “brightness” before “Calf Sidechain Compressor”.

We thus have an “Insert 1” for sending and an “Insert 2” for signal reception.

IMPORTANT!!! In Qtractor, inserts with a sending function must always have a lower number than those for receiving.

4. We right click on “Insert 2” and select: Inserts > Audio > Returns.

5. We connect outputs 1 and 2 of “Insert 1”, to inputs 3 and 4 of “Insert 2”.

6. Open “Calf Sidechain Compressor” and activate the sidechain. To ensure that it is working correctly you can activate the sidechain listener, and deactivate it after approval.

We already have all our connections!!!

Try and experiment with different configurations in “Calf Sidechain Compressor”.