[Sursound] A SDM toolbox for Matlab

[Lokki Tapio]

Dear sursounders,
Our research team has published a free toolbox to analyze, visualize, and 
reproduce spatial room impulse responses. See more:
http://www.mathworks.com/matlabcentral/fileexchange/56663-sdm-toolbox

Best,
Tapio Lokki
--
Assoc. Prof. Tapio Lokki mailto:tapio.lo...@aalto.fi>>, 
https://mediatech.aalto.fi/~ktlokki/
Aalto University School of Science, Department of Computer Science
PO Box 15500, FI-00076 Aalto, Finland, tel. +358-40-578 2486






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Re: [Sursound] Sensory evaluation of concert halls

[Lokki Tapio]

sursound-requ...@music.vt.edu kirjoitti 
21.1.2014 kello 19.00:


thanks for elaborating! very interesting method and survey!

one thing i'm asking myself: since you can only ever have one direction
per time window, does that mean that each direction estimate will
"trigger" a complete IR decay trail from the omni mic in that direction?
i.e. your directional resolution is really high, at the cost of
identical timbre of all reflections?

are there any perceptual drawbacks? i'm sure i wouldn't notice, unless
the carpet i'm standing on is knee-deep, but... :)
particularly, will the "seat dip" effect be averaged and spread into all
directions?

One time window gives one direction estimate as it is an impulse response which 
is analyzed. In ideal impulse everything (all frequencies from one direction) 
are in one sample. In practise impulses are spread in time, but the idea still 
works well. Thus, after the directional analysis all samples of one omni IR is 
distributed to reproduction loudspeakers. This results that in reproduction 
loudspeakers the convolution reverbs are quite sparse. However, after 
convolution with anechoic signal the perceived spatial sound is very natural 
without any coloration. I hope this clarifies and answer to your question.

We have not found any perceptual drawbacks. Naturally, the quality of IR is 
important, the used loudspeaker should reproduce short impulse, e.g., a dodec 
usually used in room acoustical measurements is not very good as it emits 
several impulses from all elements. And as far as I understand the "seat-dip 
effect" is correctly reproduced, but I do not have any data to prove it. At 
least it sounds the same as in-situ in real halls.

Tapio

--
Tapio Lokki mailto:tapio.lo...@aalto.fi>>, 
https://mediatech.aalto.fi/~ktlokki/
Aalto University School of Science, Department of Media Technology
PO Box 15500, FI-00076 Aalto, Finland, tel. +358-40-578 2486, fax +358-9-4702 
5014

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Re: [Sursound] Sensory evaluation of concert halls

[Lokki Tapio]

Dear surround list,
I could try to clarify a bit our recording and reproduction method, described 
in the Physics Today article:

We do recordings via impulse responses, meaning that we capture spatial impulse 
responses in the concert halls and convolve the anechoic music afterwards. This 
process is to done to get better spatial sound quality in the lab. Earlier we 
used Spatial Impulse Response Rendering (SIRR) method:
http://www.acoustics.hut.fi/research/cat/sirr/
Our current system use a method, called Spatial Decomposition Method (SDM), 
which is published in Journal of the AES:
http://www.aes.org/e-lib/browse.cfm?elib=16664, see also:
https://mediatech.aalto.fi/en/research/virtual-acoustics/research/acoustic-measurement-and-analysis/82-sdm

The SDM is a parametric method that differs significantly from spherical 
harmonics based methods. It requires at least 4 omni mics (we use 6) and the 
basic idea is as follows. An impulse response is analyzed with a short time 
window and cross-correlations between mic pairs are computed to obtain a 
time-difference-of-arrival (TDOA) in each pair. With 6 mice you get 15 TDOA 
estimates. From these time differences it can be estimated from which direction 
the sound energy is reaching the microphone array. Such analysis is done for 
every single sample (i.e. a short time window, 1ms, is shifted one sample 
forwarded after the analysis) and the final result is a normal IR + direction 
info (azi and ele) for every single sample. In the reproduction, we take an IR 
from one omni mic (to get flat frequency response) and distribute the samples 
of it to corresponding reproduction loudspeakers. In other words, we convert 
one omni IR to convolution reverbs for all reproduction loudspeakers. An
 d then we convolve the anechoic music with these loudspeaker signals 
(=convolution reverbs). In our current listening room we have 24 loudspeakers 
in a 3D setup. The accurate direction for all samples can be obtained using 
VBAP, but it attenuates high frequencies a bit. Therefore, we just associate 
every IR sample to closest reproduction loudspeaker, which might introduce a 
small error in direction, but the frequency response (and sound color) is 
untouched. With the SDM method, the most authentic reproduction (of the sound 
in the concert hall) in the lab can be obtained.

All the best,
Tapio

PS. If you want to have our JAES or JASA articles, just email be privately and 
I'll send them to you.
--
Tapio Lokki mailto:tapio.lo...@aalto.fi>>, 
https://mediatech.aalto.fi/~ktlokki/
Aalto University School of Science, Department of Media Technology
PO Box 15500, FI-00076 Aalto, Finland, tel. +358-40-578 2486, fax +358-9-4702 
5014


sursound-requ...@music.vt.edu kirjoitti 
18.1.2014 kello 19.00:

On 01/17/2014 07:29 PM, Aaron Heller wrote:
Jan 2014 Physics Today just landed on my desk and the cover article is by
Tapio Lokki on evaluation of concert halls.

"Tasting music like wine: Sensory evaluation of concert halls"

http://scitation.aip.org/content/aip/magazine/physicstoday/article/67/1/10.1063/PT.3.2242

It is labeled "free content," so should be available to anyone.


interesting. what puts me off a little is that they used an ad-hoc mic
array of six spaced omnis, without giving any details whatsoever.
how good can direction estimates be with that kind of setup? and how do
you ensure the reproduced diffuse sound field is accurate?

the actual meat is in here, it seems:
http://scitation.aip.org/content/asa/journal/jasa/133/2/10.1121/1.4770260
but sadly that one is not freely available. can't see myself paying $30
for a casual read...


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Meister f?r Veranstaltungstechnik (B?hne/Studio)
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http://stackingdwarves.net

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