Added a Sidechaining doc

_manual/17_signal-routing/08_signal-flow.html

@@ -48,14 +48,69 @@ Strict I/O is set when creating the track and can later be en/disabled dynamical
 <li>Side chain inputs are not affected by strict i/o</li>
 </ul>
 
-<h2>Customizing the Signal Flow</h2>
+<h2>Customizing the Signal Flow : The Pin Connection window</h2>
+
 <p>
 The signal flow though the mixer can be customized at every processor node via "Pin Configuration" in the context menu of every processor.
-User customization override all automatic (flexible/strict i/o mode) inferred output port settings for the given processor.
-Non-customized plugins downstream will follow suit depending on the selected route mode. e.g. adding an additional output to a plugin on a track set to strict-i/o will trickle down the process chain until the output and result in the addition of an output port.  This is useful for example in case of a mono to stereo reverb.
+User customization override all automatic (flexible/strict i/o mode) inferred output port settings </p>
+<p>
+  The Pin Connection window is made of three vertical sections:
+</p>
+<ul>
+    <li>an I/O config column</li>
+    <li>an interactive diagram</li>
+    <li>a sidechain column.</li>
+</ul>
+<p>
+  By default, the I/O config is set to <em>Automatic</em>, i.e. the <kbd class="menu">Manual Config</kbd> led light is turned off.
+  In this mode, the diagram will display the standard input/outputs for this plugin, i.e. the number of ports (input/outputs) is
+	equal to the number of pins on the plugin, and a 1:1 connection is automatically created.
+</p>
+<p>
+  Adding new instances of the plugin allows to apply this plugin to more inputs or outputs. E.g., a mono effect can be applied
+  to each channel of a <em>n</em>-channels track by adding as many instances of the plugins as there are input channels (i.e. ports). This
+  happens automatically when adding e.g. a mono effect to a stereo track:
+</p>
+<ul>
+	<li>Ardour creates two instances of the plugin,</li>
+	<li>the plugin gets a (2x1) label in the processor box</li>
+	<li>its 2 input ports are each connected to 1 pin of an instance</li>
+	<li>each mono output pin of the plugin is connected to 1 output port.</li>
+</ul>
+</p>
+<p>
+  Output channels can also, in Manual Config mode, be added or removed, be them audio or MIDI.
+</p>
+
+<p class="note">
+  Notice that using the Pin Connection overrides the I/O config setting (Flexible vs Strict). A processor <em>can</em>,
+  even in Strict I/O mode, have a different number of outputs than inputs. Non-customized plugins downstream
+	will follow suit depending on the selected route mode. e.g. adding an additional output to a plugin on a
+	track set to strict-i/o will trickle down the process chain until the output and result in the addition of
+	an output port. This is useful for example in case of a mono to stereo reverb.
 </p>
 
 <p>
-One can also bypass plugin instances with a 'trhu' connection. This connection is latency compensated. One example is separate Left/Right channel Equalization using two mono plugins on a stereo track:
+  The diagram allows to plug together the I/O ports with the plugin pins and other I/O ports, provided they are compatible (MIDI vs audio), just by
+	dragging/dropping the end connectors on one another.
+  A dotted connector's line is a "<em>thru</em>" line, that is directly connecting an output to an input without connecting to a pin on
+	the plugin, hence without any audio modification. Those "thru" connections are latency compensated with regards to those being affected by the plugin,
+  in order to avoid phasing issues. One example is separate Left/Right channel Equalization using two mono plugins on a stereo track:
+</p>
+<img src="/images/left_right_eq.png" alt="Separate left/right Eq">
+
+<p>
+	The only way to add inputs to a processor is via <a href="/signal-routing/sidechaining/">Sidechaining</a> from another signal.
+	This is done by "tapping" the signal from another track/bus at any point.
+</p>
+<p>
+	Adding a sidechain signal in Ardour is as simple as enabling the <kbd class="menu">Sidechain</kbd> button,
+	and choosing an <kbd class="menu">Audio</kbd> or <kbd class="menu">MIDI</kbd> sidechain in the
+	<kbd class="menu">Add Sidechain Input</kbd> lower right hand section.
+	A new dropdown menu appears, that displays a list of the tracks/bus available to be sidechained, or
+	for a more complex setup (e.g. sidechaining from hardware directly), the <a href="/signal-routing/Patchbay/">Routing Grid</a>
+	(also accessible with a <kbd class="mouse">Right</kbd>-click on the dropdown menu).
+</p>
+<p>
+	The sidechain ports can then be connected, as other inputs, to a pin of the plugin, or an output port for a "thru".
 </p>
-<p class="center"><img src="/images/left_right_eq.png" alt="separate left/right Eq" /></p>

_manual/17_signal-routing/09_sidechaining.html

@@ -0,0 +1,115 @@
+---
+layout: default
+title: Sidechaining
+---
+<p>
+  Dynamic Processors &ndash; such as compressors &ndash; in general use the the original
+  input signal for analysis and operate on the same signal.
+  Side-chaining uses the signal level of <em>another input</em> to control
+  the compression level of the original signal.
+</p>
+<p>
+  Effect Processors which have a side-chain input (sometimes also called <em>key input</em>)
+  have an additional input pin to receive a signal from an external input.
+  In Ardour that extra input can be connected in the plugin's <kbd class="menu">Pin Configuration</kbd>
+  dialog: the signal from one track can be tapped off and used as an input to a
+  plugin on a different track. This dialog is
+  accessed via the plugin's context-menu &gt; <kbd class="menu">Pin Connections&hellip;</kbd>.
+</p>
+<p>
+  In case a plugin has a dedicated sidechain input, Ardour automatically
+  creates a port for the input. This is a normal I/O port which can be fed by any
+  external signal.
+  The <kbd class="menu">Pin Configuration</kbd> dialog is not limited to
+  processors with a dedicated sidechain input, it also allows to manually create
+  (or remove) a sidechain input port and provides for flexible connection of the
+  signal to plugin pins.
+</p>
+<p>
+  The operational flow in the Ardour GUI starts at the processor which is to receive
+  the signal: a sidechain source is selected, and Ardour creates a dedicated send-processor in the
+  source processor box, the level of which can be adjusted either in the Pin Configuration window
+  or directly on the source's send.
+</p>
+
+<h2>A simple example: Sidechain compression</h2>
+
+<p>
+  One example is the use of a bassdrum track to trigger
+  the compression on a bass track. The sidechain compressor (a-Compressor) will be placed on
+  the bass track, and will need to receive the signal from the bassdrum track as
+  a way to trigger the compression.
+</p>
+
+<figure>
+  <img src="/images/sc-comp-pin.png" alt="Sidechain compression: Pin configuration">
+  <img src="/images/sc-comp-mixer.png" alt="Sidechain compression: Mixer view">
+  <img src="/images/sc-comp-editor.png" alt="Sidechain compression: Editor view">
+  <figcaption>
+    A sidechain compression: Pin configuration, mixer view and editor view.
+  </figcaption>
+</figure>
+
+<p>
+  Here, on the bass track, an <em>a-Compressor</em> has been added, and the
+  Drum track has been set as the sidechain source. The mixer reflects this
+  by showing an <em>SC</em>-send processor in the drum track, very similar to a <a href="/signal-routing/aux-sends/">send</a>
+  The bass track also shows an arrow as one of the a-compressor input.
+</p>
+<p>
+  As a result, in the editor, each peak in the kick drum track triggers the compression on the bass track
+  and the resulting track shows the compression kicking in on each kick drum peak, hence
+  reducing the gain. The compression is applied to the bass, but only based on the level of the drum track.
+</p>
+<p>
+  This is commonly used for <em>ducking</em> effect, when e.g. a radio speaker's voice triggers the
+  compression on the audio playing.
+</p>
+
+<h2>MIDI Sidechaining</h2>
+
+<p>
+  Ardour allows the sidechain sources to be either audio or MIDI tracks/busses. This is
+  particularly useful when a MIDI signal 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>,
+  the LV2 port of Fons Adriaensen's <a href="http://kokkinizita.linuxaudio.org/linuxaudio/zita-at1-doc/quickguide.html">Zita AT1</a>
+  by Robin Gareus:
+</p>
+
+<figure>
+  <img src="/images/pin-connection-autotune.png" alt="MIDI Sidechain">
+  <figcaption>
+    MIDI sidechainig example: fat1.lv2.
+  </figcaption>
+</figure>
+
+<p>
+  Here, the MIDI track is inputed to the plugin's MIDI IN pin through a sidechain,
+  indicating to the plugin what note should the source audio be corrected to.
+</p>
+
+<p class="note">
+  Notice that in the example above, the output of the "Vocals" track is connected
+  to the input of the "Corrected" track. We could have chosen to insert the "Vocals" track
+  content as an audio sidechain too, totally disconnecting the input from the plugin, and
+  connecting the plugin's input pin to the audio sidechain port.
+</p>
+
+<h2>Pre-processing the sidechained signal</h2>
+
+<p>
+  Sometimes, the effects of a sidechain signal on a plugin can be enhanced by
+  pre-processing the signal.
+</p>
+<p>
+  In the first example above, if the entire drum part is on one track,
+  then compressing with this signal as a sidechain will result in every peak triggering the compression,
+  be them bass drum kicks or snare, cymbals, etc.
+</p>
+<p>
+  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 instruments of the drum kit, and allow for a better triggering, though to
+  avoid damaging the original drum track, a send to an intermediary track would be better suited
+  to place the EQ on. This track won't be connected to the Master, as its content is of no musical
+  interest except for it's use as a trigger, allowing for some extreme EQ.
+</p>