188 lines
7.0 KiB
HTML
188 lines
7.0 KiB
HTML
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<h2>Overview</h2>
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<figure class="right">
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<img src="/images/track_signal_routing.png" alt="track signal routing">
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<figcaption>Typical signal routing in a channel strip.</figcaption>
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</figure>
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<p>
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In each individual Track or Bus the signal flow is top to bottom, as shown in
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the diagram on the right.
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</p>
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<p>
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Trim, Fader and Panner are provided by Ardour. The Processor Box can hold third
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party plugins or host-provided redirects (insert, aux-send, etc.).
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</p>
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<p>
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An important aspect is that the signal flow is multi-channel and not fixed
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throughout the track. For example, a track can have a mono input, a mono to
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stereo plugin (e.g. reverb) flowing into a surround panner with 6 outputs.
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</p>
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<p>
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The design of Ardour is that the width of the signal flow is defined by the
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passage through plugins in the processor box, followed by panning. The number
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of inputs to the panner is defined by the number of outputs of the last plugin
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in the chain. The number of panner outputs is equal to the track's outputs
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ports, which can be added and removed dynamically. This schema is called
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<em>Flexible I/O</em>. It is very powerful and a distinctive feature of
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Ardour.
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</p>
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<p class="note">
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The golden rule of processor signal flow: The number of outputs of one link
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of the process chain defines the number of inputs of the next, until the panner.
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</p>
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<p>
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Due to this rule there is one very common case that is hard to achieve:
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keeping a mono track mono. With <em>Flexible I/O</em>, if a stereo plugin is
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added on a mono track, the signal flow after that plugin becomes stereo.
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</p>
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<h2>Strict I/O</h2>
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<p>
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Strict I/O enforces a simple rule: plugins have the same number of inputs as
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they have outputs. By induction the track will have as many output ports as
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there are input ports.
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</p>
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<p>
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Adding a plugin will not modify the signal flow. The number of plugin outputs
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is forced to the number of inputs present at the point of insertion. If a
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plugin pin is missing, it is ignored. If a plugin pin is not connected, it is
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fed with silence. Non-connected plugin outputs are ignored.
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</p>
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<p>
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Strict I/O enforces the number of output ports. The number of inputs to the
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panner (outputs of last plugin) defines the number of track outputs (after
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panner). Required ports are automatically added, excess ports are removed.
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The user cannot manually add or remove output ports.
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</p>
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<p>
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Strict I/O is set when creating the track and can later be enabled or
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disabled dynamically in the context menu of every mixer strip.
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</p>
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<figure class="center">
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<img src="/images/strict_io_routing.png" alt="strict I/O routing" />
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<figcaption class=center>Flexible vs. Strict I/O.</figcaption>
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</figure>
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<p>
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There are two exceptions to the above rule:
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</p>
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<ul>
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<li>Midi Synths. When adding a synth at a point where there is a Midi port
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only, the synthesizer plugin will add audio output ports, which trickle down
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the processor chain to all follow up plugins as inputs and in turn force
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their outputs to match</li>
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<li>Side chain inputs are not affected by Strict I/O</li>
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</ul>
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<h2>Customizing the Signal Flow: The Pin Connection window</h2>
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<p>
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The signal flow though the mixer can be customized at every processor node
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via <kbd class=menu>Pin Configuration</kbd> in the context menu of every
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processor. User customization overrides all automatic (Flexible and Strict
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I/O mode) inferred output port settings.
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</p>
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<p>
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The Pin Connection window is made of three vertical sections:
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</p>
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<ul>
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<li>an I/O config column</li>
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<li>an interactive diagram</li>
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<li>a sidechain column</li>
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</ul>
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<p>
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By default, the I/O config is set to <em>Automatic</em>, i.e. the <kbd
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class="menu">Manual Config</kbd> LED light is turned off. In this mode, the
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diagram will display the standard input/outputs for this plugin, i.e. the
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number of ports (inputs & outputs) is equal to the number of pins on the
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plugin, and a one-to-one connection is automatically created.
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</p>
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<p>
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Adding new instances of the plugin allows to apply this plugin to more inputs
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or outputs. E.g., a mono effect can be applied to each channel of a
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<em>n</em>-channels track by adding as many instances of the plugins as there
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are input channels (i.e. ports). This happens automatically when adding,
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e.g., a mono effect to a stereo track:
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</p>
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<ul>
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<li>Ardour creates two instances of the plugin</li>
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<li>the plugin gets a (2x1) label in the processor box</li>
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<li>its two input ports are each connected to one pin of an instance</li>
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<li>each mono output pin of the plugin is connected to one output port</li>
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</ul>
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<p>
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Output channels can also, in Manual Config mode, be added or removed, whether
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they are audio or MIDI.
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</p>
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<p class="note">
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Using the Pin Connection overrides the I/O config setting (Flexible vs.
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Strict). A processor <em>can</em>, even in Strict I/O mode, have a different
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number of outputs than inputs. Non-customized plugins downstream will follow
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suit depending on the selected route mode. e.g. adding an additional output
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to a plugin on a track set to Strict I/O will trickle down the process chain
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to the output and result in the addition of an output port. This is useful
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for example in case of a mono to stereo reverb.
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</p>
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<p>
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The window allows connection of the I/O ports to the plugin pins and other
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I/O ports, provided they are compatible (MIDI vs. audio), just by dragging
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and dropping the end connectors on top of one another. A dotted connector's
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line is a "<em>thru</em>" line that directly connects an input to an output
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without connecting to a pin on the plugin—hence without any audio
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modification. These "thru" connections are latency compensated, with respect
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to those being affected by the plugin, in order to avoid phasing issues.
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</p>
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<p>
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An example of using "thru" connections, shown below, is separate left/right
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channel equalization using two mono plugins on a stereo track:
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</p>
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<figure class=center>
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<img src="/images/left_right_eq.png" alt="Separate left/right Eq">
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<figcaption class=center>An example of using two mono plugins on a stereo track.</figcaption>
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</figure>
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<p>
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The only way to add inputs to a processor is via
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<a href="@@sidechaining">Sidechaining</a> from another signal.
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This is done by "tapping" the signal from another track or bus at any point.
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</p>
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<p>
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Adding a sidechain signal in Ardour is as simple as enabling the <kbd
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class="menu">Side Chain</kbd> button in the Pin Configuration window, and
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choosing an <kbd class="menu">Audio</kbd> or <kbd class="menu">MIDI</kbd>
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sidechain in the <kbd class="menu">Add Sidechain Input</kbd> lower right hand
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section. A new drop-down menu appears, which displays a list of the
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tracks/busses available to be sidechained, or, for a more complex setup (e.g.
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sidechaining from hardware directly), the
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<a href="@@patchbay">Routing Grid</a> (also accessible with a
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<kbd class="mouse">Right</kbd>-click on the drop-down menu).
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</p>
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<p>
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The sidechain ports can then be connected, as other inputs, to a pin of the
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plugin, or an output port as a "thru".
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</p>
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