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