Dear member of the list,

I wanted to ask for some opinions\advice about multichannel reverb.

Some background first:
I'm emailing on behalf of Earfilms <http://www.earfilms.com/>: We are
currently in the process of producing our first show for a 19 speaker
sound-system (arranged on a dome + 4 subs on the floor). We have a custom
spatialisation system utilising 3rd order ambisonics, ambipanning and vbap.
We would like to incorporate a 'proper' multichannel reverb, which would
take into consideration the position of the sound source within the virtual
space and render the result into 19 discrete channels. We are looking
either to buy\use ready made software or to develop our own. We use MaxMSP
for spatialisation but we could easily incorporate anything available in
Csound, Supercolider or other such software as long as it can be controlled
via OSC.

The options we are aware of are the following:

   1. using algorithmic reverb like the one in IRCAM''s SPAT (max msp
   version since the plugin is limited to 8 channel output)
   2. using a custom made convolution reverb: 1st order ambisonics IR (4
   channels) convolved with 1st order components of panned sound sources
      - The simple case: one 4channel 1st-order IR
      - more complex: multiple 1st-order IR's recorded with the source of
      the impulse placed in different positions within the space

First, I would like to ask for opinions about the quality of the SPAT
reverb (max msp version). Does it sond convincing? How much better is it
then just using a stereo reverb somehow distributed between all available
speakers? We'd be happy to pay for IRCAM forum subscription if we knew what
we are paying for. Unfortunately we haven't been able to put our hands on a
copy of the externals so we can try it out ourselves.

Secondly, if we go the second route, we are aware we'd have to get the IR's
from somwhere. Are there any free\comercial 1st order IR's out there? We
will not be able to record our own, so we were looking into synthesising
some using ray-tracing software. I found this commercial one:
http://www.quikquak.com/Prod_RaySpace.html and a matlab code in the
following paper:
http://home.tiscali.nl/ehabets/rir_generator/rir_generator.pdf. Does any
one know any alternatives?

Another issue when implementing a reverb with the multiple IR's (multi
source), has it been established in any way what is the best practice when
crossfading between the IR's when the source moves? Should the closest 2
IR's be used and just crossfaded based on distance?

Any further though about the subject, as well as links to
literature\research would be highly appreciated.

Thanks you for your time!

-- 
Adrian Gierakowski
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