manual/include/io-plugins.html

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<p>
I/O plugins are a way to process audio outside the normal Ardour session or
connect to sources typically unavailable in a DAW, such as outputs of NDI
devices. Pre-plugins run before Ardour does any processing, post-plugins run
after Ardour has done all processing.
</p>
<p>
A common use case is wet recording where a number of plugins are applied
directly to the physical input. The processed signal then can be routed to any
number of tracks or busses in Ardour. This is a lot like doing some of the
processing with a chain of guitar pedals, then feeding the signal to an Aux In
port on a mixing console or an input port on a multi-effects digital
pedalboard.
</p>
<p>
The rationale for pre-processing with I/O plugins is that it's a more
lightweight way to do it as compared to busses. Much of that is because busses
have automatable parameters such as fader and panner positions, as well as
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plugins' parameters. Evaluating parameter automation (even when there's none)
adds additional load to the CPU. However I/O plugins are not automatable, so
there's no evaluation happening. As far as Ardour is concerned, they are
almost like JACK audio server clients running alongside Ardour.
</p>
<p>
Another use case would be loading an instance of the NDI Input plugin as a
pre-processing plugin to be able to capture and mix sources from NDI devices,
or loading an instance of the NDI Output plugin to send audio from Ardour over
IP to a receiver for broadcasting.
</p>
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<figure>
<img style="width:50%;" width="50%" src="/images/io-plugins-ndi-input.png" alt="NDI Input plugin loaded as a pre-processing I/O plugin">
<figcaption>NDI Input plugin loaded as a pre-processing I/O plugin</figcaption>
</figure>
<p>
It's also possible to use the post-processing section to load plugins for room
correction or signal analysis (VU meters, spectrum analyzers etc.).
</p>
<h2>Adding I/O plugins</h2>
<p>
New I/O plugins can be added in the <kbd class="title">I/O Plugins</kbd>
dialog (<kbd class="menu">Window &gt; I/O Plugins</kbd>).
</p>
<figure>
<img style="width:50%;" width="50%" src="/images/io-plugins-empty-slots.png" alt="Empty slots in the I/O Plugins dialog">
<figcaption>Empty slots in the I/O Plugins dialog</figcaption>
</figure>
<p>
Right-clicking opens the same menu for plugin selection available for mixer
channel strips:
</p>
<figure>
<img style="width:50%;" width="50%" src="/images/io-plugins-right-click-menu.png" alt="Right-click menu in the I/O Plugins dialog">
<figcaption>Right-click menu in the I/O Plugins dialog</figcaption>
</figure>
<p>
Double-clicking opens the <kbd class="title">Plugin Selector</kbd> dialog.
</p>
<p>
Once a plugin has been selected and added, it shows in either Pre- or
Post-process section depending on your choice.
</p>
<figure>
<img style="width:50%;" width="50%" src="/images/io-plugins-one-plugin-added.png" alt="ACE Compressor added to the pre- section">
<figcaption>ACE Compressor added to the Pre-process section</figcaption>
</figure>
<h2>Routing I/O plugins</h2>
<p>
I/O plugins have the same user interface for setting input and outputs that is
also available in mixer channel strips. The button above the plugin name opens
a drop-down menu for quickly choosing an input port. The button below opens
the drop-down menu for choosing the output port.
</p>
<figure>
<img style="width:50%;" width="50%" src="/images/io-plugins-choose-output.png" alt="Choosing output for an I/O plugin">
<figcaption>Choosing output for an I/O plugin</figcaption>
</figure>
<p>
Additionally, new tracks automatically connected to an I/O plugin can be
easily created in the <kbd class="title">Recorder</kbd> window by clicking the
<kbd class="key">+</kbd> button and then setting a new for that track.
</p>
<figure>
<img style="width:50%;" width="50%" src="/images/io-plugins-new-track-from-io-plugin.png" alt="New track connected to an I/O plugin">
<figcaption>New track connected to an I/O plugin</figcaption>
</figure>