106 lines
4.9 KiB
HTML
106 lines
4.9 KiB
HTML
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<p>
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Dynamic Processors—such as compressors—in general use the the original input signal for analysis and operate on
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the same signal. Side-chaining uses the signal level of <em>another input</em> to control the compression level of the
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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>) have an additional input pin to
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receive a signal from an external input. In Ardour that extra input can be connected in the plugin's <kbd class="menu">Pin
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Configuration</kbd> dialog: the signal from one track can be tapped off and used as an input to a plugin on a different
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track. This dialog is 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 creates a port for the input. This is a normal I/O
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port which can be fed by any external signal. 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 (or remove) a sidechain input port and
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provides for flexible connection of the 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 the signal: a sidechain source is
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selected, and Ardour creates a dedicated send-processor in the source processor box, the level of which can be adjusted
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either in the Pin Configuration window 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 bass drum track to trigger the compression on a bass track. The sidechain compressor
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(a-Compressor) will be placed on the bass track, and will need to receive the signal from the bass drum track as a way to
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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 Drum track has been set as the sidechain source.
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The mixer reflects this by showing an <em>SC</em>-send processor in the drum track, very similar to a
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<a href="@@aux-sends">send</a>. 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 and the resulting
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track shows the compression kicking in on each kick drum peak, hence reducing the gain. The compression is applied to the
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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 compression on the audio
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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 particularly useful when a MIDI signal
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is used to control an audio effect, like a 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
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AT1</a> 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 sidechaining 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 inputted to the plugin's MIDI IN pin through a sidechain, indicating to the plugin what note the source audio should 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 to the input of the "Corrected" track. We
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could have chosen to insert the "Vocals" track content as an audio sidechain too, totally disconnecting the input from the
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plugin, and 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 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, then compressing with this signal as a sidechain will
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result in every peak triggering the compression, be they 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 created by the high pitched
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instruments of the drum kit, and allow for a better triggering, though to avoid damaging the original drum track, a send to
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an intermediary track would be better suited to place the EQ on. This track won't be connected to the Master, as its content
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is of no musical interest except for its use as a trigger, allowing for some extreme EQ.
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</p>
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