[PD] HOA / spatialization approaches for a hemisphere

[jmejia at anestheticaudio.com]

Thanks Winfried - this looks exciting! Digging into this library now!

-Jesse 

On 2017-06-29 11:00, Winfried Ritsch wrote:

> Hello,
> 
> Theoretically, with Ambisonics any configuration of loudspeaker outside a 
> listening spot, with speaker in distance which Produce a kind of plane 
> wavefield  is suitable for Ambisonics.  The better the speaker sound, the 
> better the whole system, but it is robust for individual speaker differences 
> as long you calibrate it and has a way better energy distribution than vbap 
> for small speaker. Of course, if speaker missing on some side there can be no 
> sound from there, but placing virtual speaker for decoder makes smoother 
> transistions to this direction and so on, best follow the advices in 
> Ambisonics Decoder Toolbox [ADT] by Aaron J. Heller [1 [1]]  to calculate a 
> decoder.
> 
> Anyhow we are on the way for a Pd Ambisonics library for "Imperfect Ambisonics 
> Systems". Which also means in rooms with "bad acoustics" or any other odd 
> places, mixed speaker setup and so on. You are invited to join to extend this 
> simple abstraction lib.
> 
> https://git.iem.at/pd/acre-amb
> 
> By the way it supports multichannel patching with names as buses and so on, to 
> reduce Pd-cabling. (Note it is in development and should be stable end of 
> summer).
> 
> Next week we want to finalize the new Ambisonics domeplayer [2 [2]] for AAAS 
> (affordable autonomous Ambisonics system) for the workshop in September (and 
> publish it on git).
> 
> [1]  https://bitbucket.org/ambidecodertoolbox/adt.git )
> [2] https://iaem.at/kurse/projekte/aaas2/iemkit_6ch.jpg
> 
> rfc
> winfried
> 
> Am Samstag, 24. Juni 2017, 11:26:59 schrieb Pierre Guillot: Hi Jesse,
> 
> With Ambisonics, ideally your loudspeakers should discretize perfectly a
> sphere, you should have your head at the exact center of this sphere, etc.
> and perhaps if you forget that your head interferes and the loudspeakers
> don't generate plane waves you'll be able to reconstruct a coherent sound
> field... But to avoid these restrictions (because very few people have a
> full sphere of loudspeakers - or want to ask the audience to be completely
> crushed at the center of the sphere) there are several techniques :
> optimizations of the energy and/or velocity vectors, optimizations of the
> decoding, etc. The problem is that none of the solutions are completely
> generic. Your choice must be driven by your approach and your goal.The
> advantage of Ambisonics lies in its intermediary representation of the
> sound field that allows to apply transformations (rotation or whatever) and
> to decode for different loudspeakers configurations. But if you just want
> to spatialize individuals point sources, you can also use VBAP that is
> perhaps much more accessible. Nevertheless yes, you can surely find a way
> to decode the sound field for two ring of loudspeakers with Ambisonics (we
> can discuss it if you want). And one good rule is just to avoid placing
> sources where the loudspeakers are missing. I don't know if I really answer
> the question, I hope a bit :)
> 
> Cheers,
> 
> Pierre
> 
> Date: Fri, 23 Jun 2017 16:19:29 -0600
> From: jmejia at anestheticaudio.com
> To: pd-list at lists.iem.at
> Subject: [PD] HOA / spatialization approaches for a hemisphere
> Message-ID: <3149263781acf8439b762eef943d60e5 at anestheticaudio.com>
> Content-Type: text/plain; charset="utf-8"
> 
> Hi List,
> 
> I'm putting together a 32 channel HDLA and looking for spatialization
> advice. The configuration will be two rings, one higher than the other,
> and I've been thinking a bit smaller/closer to approximate a hemisphere.
> But that's flexible - they could be parallel rings if it simplifies
> things.
> 
> I have some (limited) experience using HoaLibrary + PD for 2D ambisonics
> - so my initial thought was to try the 3d externals there - however I'm
> not sure if it actually makes sense to build an abstraction setup for a
> sphere of twice as many channels while limiting access to the upper
> hemisphere only. I'm assuming there would be some problems with that
> approach.
> 
> I found a few papers on mixed-order ambisonics - by Chris Travis and
> also the AmbiX crew - but I'm not sure if there's away to implement that
> stuff with HoaLibrary. I'm also open to using different software if
> something else is recommended instead.
> 
> Thanks for any advice!
> 
> -Jesse
 

Links:
------
[1] https://bitbucket.org/ambidecodertoolbox/adt.git
[2] https://iaem.at/kurse/projekte/aaas2/iemkit_6ch.jpg
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