[PD] HOA / spatialization approaches for a hemisphere

[jmejia at anestheticaudio.com]

Thanks Pierre - these abstractions seem great! I was able to easily
adapt it to work with my setup. 

I've been looking over Ville Pulki's paper but am a bit lost as to how
to implement a spread function in your abstractions. Can you point me in
the right direction? 

Thanks! 

-Jesse

On 2017-06-27 01:18, Pierre Guillot wrote:

> My VBAP repository is for "personal" use, I'm not sure that I will ever publish an "official" release but everything should work ! I did this because there were bugs in the "official" implementation when using a very large number of loudspeakers and I couldn't solve the problem from the original code (I couldn't find the problem in fact...). If you want to be sure to have something durable I suggest you to use the abstraction p.vbap but the compiled externals are much more efficient. One last thing: there is no "spread" factor (MDBAP)  but you can do it manually in Pd. The principles are explained in the paper Uniform Spreading Of Amplitude Panned Virtual Sources (https://aaltodoc.aalto.fi/bitstream/handle/123456789/2345/article4.pdf) and the implementation is explained in Generic panning tools for MAX/MSP (http://cnmat.org/ICMC2000/pdf/VBAP.pdf).  
> Cheers 
> 
> 2017-06-25 0:09 GMT+02:00 <jmejia at anestheticaudio.com>:
> 
> Thanks Pierre! That's all great advice. I'm gonna dig into VBAP - it's been awhile since I've messed with that. Maybe that will work better. 
> 
> I'll give your building repo a shot https://github.com/pierreguillot/vbap [1] 
> 
> (unless you have OSX binaries?)  
> 
> but I also wonder about all these others: 
> 
> https://puredata.info/downloads/vbap/releases [2] 
> 
> vbap-v0 on dekken 
> 
> https://sourceforge.net/projects/pure-data/files/libraries/vbap/ [3] 
> 
> Thanks! 
> 
> -Jesse
> 
> On 2017-06-24 03:26, Pierre Guillot wrote: 
> 
> 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://github.com/pierreguillot/vbap
[2] https://puredata.info/downloads/vbap/releases
[3] https://sourceforge.net/projects/pure-data/files/libraries/vbap/
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