116 lines
5.0 KiB
HTML
116 lines
5.0 KiB
HTML
---
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layout: default
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title: Sidechaining
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---
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<p>
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Dynamic Processors – such as compressors – in general use the the original
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input signal for analysis and operate on the same signal.
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Side-chaining uses the signal level of <em>another input</em> to control
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the compression level of the original signal.
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</p>
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<p>
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Effect Processors which have a side-chain input (sometimes also called <em>key input</em>)
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have an additional input pin to receive a signal from an external input.
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In Ardour that extra input can be connected in the plugin's <kbd class="menu">Pin Configuration</kbd>
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dialog: the signal from one track can be tapped off and used as an input to a
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plugin on a different track. This dialog is
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accessed via the plugin's context-menu > <kbd class="menu">Pin Connections…</kbd>.
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</p>
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<p>
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In case a plugin has a dedicated sidechain input, Ardour automatically
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creates a port for the input. This is a normal I/O port which can be fed by any
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external signal.
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The <kbd class="menu">Pin Configuration</kbd> dialog is not limited to
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processors with a dedicated sidechain input, it also allows to manually create
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(or remove) a sidechain input port and provides for flexible connection of the
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signal to plugin pins.
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</p>
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<p>
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The operational flow in the Ardour GUI starts at the processor which is to receive
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the signal: a sidechain source is selected, and Ardour creates a dedicated send-processor in the
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source processor box, the level of which can be adjusted either in the Pin Configuration window
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or directly on the source's send.
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</p>
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<h2>A simple example: Sidechain compression</h2>
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<p>
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One example is the use of a bassdrum track to trigger
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the compression on a bass track. The sidechain compressor (a-Compressor) will be placed on
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the bass track, and will need to receive the signal from the bassdrum track as
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a way to trigger the compression.
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</p>
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<figure>
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<img src="/images/sc-comp-pin.png" alt="Sidechain compression: Pin configuration">
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<img src="/images/sc-comp-mixer.png" alt="Sidechain compression: Mixer view">
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<img src="/images/sc-comp-editor.png" alt="Sidechain compression: Editor view">
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<figcaption>
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A sidechain compression: Pin configuration, mixer view and editor view.
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</figcaption>
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</figure>
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<p>
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Here, on the bass track, an <em>a-Compressor</em> has been added, and the
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Drum track has been set as the sidechain source. The mixer reflects this
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by showing an <em>SC</em>-send processor in the drum track, very similar to a <a href="/signal-routing/aux-sends/">send</a>
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The bass track also shows an arrow as one of the a-compressor input.
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</p>
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<p>
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As a result, in the editor, each peak in the kick drum track triggers the compression on the bass track
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and the resulting track shows the compression kicking in on each kick drum peak, hence
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reducing the gain. The compression is applied to the bass, but only based on the level of the drum track.
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</p>
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<p>
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This is commonly used for <em>ducking</em> effect, when e.g. a radio speaker's voice triggers the
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compression on the audio playing.
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</p>
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<h2>MIDI Sidechaining</h2>
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<p>
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Ardour allows the sidechain sources to be either audio or MIDI tracks/busses. This is
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particularly useful when a MIDI signal is used to control an audio effect, like a
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vocoder or an auto-tuner, like <a href="https://github.com/x42/fat1.lv2">fat1</a>,
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the LV2 port of Fons Adriaensen's <a href="http://kokkinizita.linuxaudio.org/linuxaudio/zita-at1-doc/quickguide.html">Zita AT1</a>
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by Robin Gareus:
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</p>
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<figure>
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<img src="/images/pin-connection-autotune.png" alt="MIDI Sidechain">
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<figcaption>
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MIDI sidechainig example: fat1.lv2.
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</figcaption>
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</figure>
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<p>
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Here, the MIDI track is inputed to the plugin's MIDI IN pin through a sidechain,
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indicating to the plugin what note should the source audio be corrected to.
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</p>
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<p class="note">
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Notice that in the example above, the output of the "Vocals" track is connected
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to the input of the "Corrected" track. We could have chosen to insert the "Vocals" track
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content as an audio sidechain too, totally disconnecting the input from the plugin, and
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connecting the plugin's input pin to the audio sidechain port.
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</p>
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<h2>Pre-processing the sidechained signal</h2>
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<p>
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Sometimes, the effects of a sidechain signal on a plugin can be enhanced by
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pre-processing the signal.
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</p>
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<p>
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In the first example above, if the entire drum part is on one track,
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then compressing with this signal as a sidechain will result in every peak triggering the compression,
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be them bass drum kicks or snare, cymbals, etc.
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</p>
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<p>
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In this case, adding an EQ to the drum track with a low pass filter would filter out the peaks
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created by the high pitched instruments of the drum kit, and allow for a better triggering, though to
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avoid damaging the original drum track, a send to an intermediary track would be better suited
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to place the EQ on. This track won't be connected to the Master, as its content is of no musical
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interest except for it's use as a trigger, allowing for some extreme EQ.
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</p>
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