[PD] 6 speakers in a circle, ambi? vbap?

Nicholas Mariette nicholas.mariette at limsi.fr
Mon Oct 6 12:18:55 CEST 2008

hi Hans,

VBAP is probably better if you expect people to move around in the  
installation space and you wish to pan individual sounds in different  
First order ambisonics works fine on 6 speakers, but it would be more  
suited to immersive, enveloping ambient sounds, or a more constrained  

Horizontal VBAP will use only the nearest 2 speakers to simulate a  
sound in one direction, while ambisonics decoding will generally use  
all speakers for the same simulated sound source.  Thus VBAP sounds  
will often seem to "snap to speaker positions" when panning around the  
circle, whereas ambisonic panned sounds will not reveal the individual  
speakers as much, but the illusion will not work as well away from the  
centre of the room.

I like the description I heard recently from Bruce Wiggins on the  
difference between VBAP and ambisonics - that VBAP is exactly correct  
for panning a sound when it's in the direction of a speaker, but quite  
wrong when panning exactly in-between two speakers.  Ambisonics on the  
other hand is "equally wrong" (to a lesser degree than VBAP between  
speakers) for a sound in any direction.

In many cases, the best spatialisation solution could be a mixture of  
both VBAP (for directional sounds) and ambisonic (for spatial  
ambience) - unless the audience isn't able to get too close to the  
speakers, or you use higher order ambisonics.

The IEM ambi stuff is all in Pd extended browser... I guess you've  
seen that.
I've attached some patches that I have for encoding to quad.

Only problem is the latest 2 releases of Pd extended seem to have  
problems loading mtx_*~ object.
I got it working with Pd extended 0.39.3

Output is for 4 speakers, but it's easy enough to change the speaker  
specifications in the nmg_bf2quad~  abstraction - go into the pd calc- 
matrix subpatch, make up a new speaker spec, print the decode matrix  
and copy that back into the patch.

Hope this helps.

Nick Mariette

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On Oct 6, 2008, at 6:39 AM, Hans-Christoph Steiner wrote:

> So I am working on sound for a permanent installation involving 6
> speakers in a large circular room.  Are 6 speakers enough to do
> anything useful using ambisonics?  Or am I better off using the
> simpler vbap?
> I am just starting to understand the basics of ambisonics, thanks to
> Florian's intro.  I will be programmatically controlling the position
> of the samples, since it will be synced up with a video.  So I don't
> think I really need the GUIs like cubemixer.
> Are there any simple, working demos of the IEM ambi stuff?
> .hc
> ------------------------------------------------------------------------
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