preliminary VBAP panner docs

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 title: VBAP Panner
 ---                        
 
+<div class="well notabene">
+  Ardour's VBAP panner is currently in development, and its semantics may
+  change in the near future, possibly affecting your mixes. Please do not
+  rely on it for important production work while the dust settles.
+</div>
+<p>
+  <strong>VBAP</strong> is short for <em>Vector-base Amplitude Panning</em>, 
+  a versatile and
+  straightforward method to pan a source around on an arbitrary number
+  of speakers on a horizontal polygon or a 3D surface, even if the speaker
+  layout is highly irregular.
+</p>
+
+<h2>Basic concepts</h2>
+<p>
+  VBAP was developed by Ville Pulkki at Aalto University, Helsinki, in 2001.
+  It works by distributing the signal to the speakers nearest to the desired
+  direction with appropriate weightings, aiming to create a maximally sharp 
+  phantom source by using as few speakers as possible:
+</p>
+<ul>
+  <li>one speaker, if the desired direction coincides with a speaker
+  location,</li>
+  <li>two speakers, if the desired direction is on the line between two
+  speakers,</li>
+  <li>and three speakers in the general 3D case.</li>
+</ul>
+<p>
+  Thus, if you move the panner onto a speaker, you can be sure that only
+  this speaker will get any signal. This is handy when you need precise
+  1:1 routing.<br />
+  The drawback of VBAP is that a moving source will constantly change its 
+  apparent sharpness, as it transitions between the three states mentioned 
+  above.
+</p>
+<p>
+  A horizontal VBAP panner has one parameter, the <strong>azimuth
+  angle</strong>. A 3D panner offers an additional <strong>elevation
+  angle</strong> control.
+</p>
+<div class="well">
+  More elaborate implementations of VBAP also include a
+  <strong>spread</strong> parameter, which  will distribute the signal over a 
+  greater number of speakers in order to maintain constant (but no longer 
+  maximal) sharpness, regardless of position. Ardour's VBAP panner does not 
+  currently include this feature.
+</div>
+
+<h2>Speaker layout</h2>
+<p>
+  Each VBAP panner is specific to its <strong>speaker layout</strong>
+  &mdash; the panner has
+  to "know" about the precise location of all the speakers. A complete VBAP
+  implementation must therefore include the possibility to define this
+  layout.
+</p>
+<img src="/images/VBAP-panner-5.png" class="small right"/>
+<p>
+  Ardour currently uses a simplified approach: if a track or bus has more
+  than two output channels (which implies stereo), it assumes that you
+  have N speakers distributed in a regular N-gon. That means that for
+  irregular layouts such as 5.1 or 7.1, the direction you dial in will
+  differ a bit from the actual auditory result, but you can still achieve
+  any desired spatialisation.
+</p>
+<h3>Experimental 3D VBAP</h3>
+<img src="/images/VBAP-panner-10.png" class="small right"/>
+<p>
+  For tracks with 10 outputs, Ardour will currently assume a 3-dimensional
+  speaker layout corresponding to Auro-3D 10.1, which is a horizontal 5.1
+  system, four elevated speakers above L, R, Ls, and Rs, and an additional
+  "voice-of-god" speaker at the zenith.
+</p>
+
+<h2>N:M panning</h2>
+<img src="/images/VBAP-panner-4in5.png" class="small right"/>
+<p>
+  For tracks and busses with more than one input, Ardour will (for now) assume that
+  you wish to distribute the inputs symmetrically along the latitude around
+  the panner direction. The width parameter controls the opening angle of
+  the distribution sector.
+</p>
+
+
+
+

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