5 In each individual Track or Bus the signal flow is top to bottom. Consider
10 <img width="360px" src="/images/track_signal_routing.png" alt="track signal routing" />
11 <figcaption class=center>Typical signal routing in a channel strip.</figcaption>
15 Trim, Fader and Panner are provided by Ardour. The Processor Box can hold 3rd
16 Party Plugins or host-provided redirects (insert, aux-send, etc.).
20 An important aspect is that the signal flow is multi-channel and not fixed
21 throughout the track. For example, a Track can have a mono input, a mono to
22 stereo plugin (e.g. reverb) flowing into a surround panner with 6 outputs.
23 The design of Ardour is that width of the signal flow is defined by the
24 passage through plugins in the processor box, followed by panning. The number
25 of inputs to the panner is defined by the number outputs of the last plugin
26 in the chain. The number of panner outputs is equal to the track's outputs
27 ports, which can be added and removed dynamically. This schema is called
28 <em>Flexible I/O</em>. It is very powerful and a distinctive feature of
33 The golden rule of processor signal flow: The number of outputs of one link
34 of the process chain defines the number inputs of the next, until the panner.
38 Due to this rule there is one very common case that is hard to achieve:
39 keeping a mono track mono. With <em>Flexible I/O</em>, if a stereo plugin is
40 added on a mono track, the signal flow after that plugin becomes stereo.
46 Strict I/O enforces a simple rule: Plugins have the same number of inputs as
47 they have outputs. By induction the track will have as many output ports as
48 there are input ports.
52 Adding a Plugin will not modify the signal flow. The number of plugin outputs
53 is forced to the number of inputs present at the point of insertion. If a
54 plugin pin is missing, it is ignored. If a plugin pin is not connected, it is
55 fed with silence. Non-connected plugin outputs are ignored.
59 Strict I/O enforces the number of output ports. The number of inputs to the
60 panner (outputs of last plugin) defines the number of track outputs (after
61 panner). Required ports are automatically added, excess ports are removed.
62 The user cannot manually add or remove output ports.
66 Strict I/O is set when creating the track and can later be enabled or
67 disabled dynamically in the context menu of every mixer strip.
70 <figure class="center">
71 <img src="/images/strict_io_routing.png" alt="strict I/O routing" />
72 <figcaption class=center>Flexible vs. Strict I/O.</figcaption>
76 There are two exceptions to the above rule:
80 <li>Midi Synths. When adding a synth at a point where there is a Midi port
81 only, the synthesizer plugin will add audio output ports, which trickle down
82 the processor chain to all follow up plugins as inputs and in turn force
83 their outputs to match</li>
84 <li>Side chain inputs are not affected by Strict I/O</li>
87 <h2>Customizing the Signal Flow: The Pin Connection window</h2>
90 The signal flow though the mixer can be customized at every processor node
91 via <kbd class=menu>Pin Configuration</kbd> in the context menu of every
92 processor. User customization overrides all automatic (Flexible and Strict
93 I/O mode) inferred output port settings.
97 The Pin Connection window is made of three vertical sections:
101 <li>an I/O config column</li>
102 <li>an interactive diagram</li>
103 <li>a sidechain column</li>
107 By default, the I/O config is set to <em>Automatic</em>, i.e. the <kbd
108 class="menu">Manual Config</kbd> led light is turned off. In this mode, the
109 diagram will display the standard input/outputs for this plugin, i.e. the
110 number of ports (inputs & outputs) is equal to the number of pins on the
111 plugin, and a one-to-one connection is automatically created.
115 Adding new instances of the plugin allows to apply this plugin to more inputs
116 or outputs. E.g., a mono effect can be applied to each channel of a
117 <em>n</em>-channels track by adding as many instances of the plugins as there
118 are input channels (i.e. ports). This happens automatically when adding,
119 e.g., a mono effect to a stereo track:
123 <li>Ardour creates two instances of the plugin</li>
124 <li>the plugin gets a (2x1) label in the processor box</li>
125 <li>its two input ports are each connected to one pin of an instance</li>
126 <li>each mono output pin of the plugin is connected to one output port</li>
130 Output channels can also, in Manual Config mode, be added or removed, whether
131 they are audio or MIDI.
135 Using the Pin Connection overrides the I/O config setting (Flexible vs.
136 Strict). A processor <em>can</em>, even in Strict I/O mode, have a different
137 number of outputs than inputs. Non-customized plugins downstream will follow
138 suit depending on the selected route mode. e.g. adding an additional output
139 to a plugin on a track set to Strict I/O will trickle down the process chain
140 to the output and result in the addition of an output port. This is useful
141 for example in case of a mono to stereo reverb.
145 The window allows connection of the I/O ports to the plugin pins and other
146 I/O ports, provided they are compatible (MIDI vs. audio), just by dragging
147 & dropping the end connectors on top of one another. A dotted connector's
148 line is a "<em>thru</em>" line that directly connects an input to an output
149 without connecting to a pin on the plugin—hence without any audio
150 modification. These "thru" connections are latency compensated, with respect
151 to those being affected by the plugin, in order to avoid phasing issues.
155 An example of using "thru" connections, shown below, is separate left/right
156 channel equalization using two mono plugins on a stereo track:
159 <figure class=center>
160 <img src="/images/left_right_eq.png" alt="Separate left/right Eq">
161 <figcaption class=center>An example of using two mono plugins on a stereo track.</figcaption>
165 The only way to add inputs to a processor is via
166 <a href="/signal-routing/sidechaining/">Sidechaining</a> from another signal.
167 This is done by "tapping" the signal from another track or bus at any point.
171 Adding a sidechain signal in Ardour is as simple as enabling the <kbd
172 class="menu">Side Chain</kbd> button in the Pin Configuration window, and
173 choosing an <kbd class="menu">Audio</kbd> or <kbd class="menu">MIDI</kbd>
174 sidechain in the <kbd class="menu">Add Sidechain Input</kbd> lower right hand
175 section. A new dropdown menu appears, which displays a list of the
176 tracks/busses available to be sidechained, or, for a more complex setup (e.g.
177 sidechaining from hardware directly), the
178 <a href="/signal-routing/Patchbay/">Routing Grid</a> (also accessible with a
179 <kbd class="mouse">Right</kbd>-click on the dropdown menu).
183 The sidechain ports can then be connected, as other inputs, to a pin of the
184 plugin, or an output port as a "thru".