[PD] HOA / spatialization approaches for a hemisphere

[Winfried Ritsch]

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]  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] 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

-- 
---
Ritsch, Winfried, Ao.Univ.Prof. Dipl.-Ing.
   Institut 17 Elektronische Musik und Akustik
   8010 Graz, Inffeldgasse 10/III
E-Mail 	ritsch at iem.at
Homepage 	http://iem.at/~ritsch
Mobil 	++436642439369
---