The distance (technically, "range" - from perceiver to source- -) problem
encountered in "giant geese: (John Leonard's ambisonic recording of close-miked
geese played over a large, <30m radius rig) was the disparity in subtended
angles produced by the decorrelation across any image with non-neglible ASW
(apparent source width) in combination with a perceptiual constancy for speaker
distance in any non-anechoic performance site.
As Dave says, we had fun with several examples of 'blown up' images - a giant
toilet (with high-flush cistern), a VW (mine) that approached plausibly enough,
then as it traversed the speaker array - whose radius was significantly greater
than the mic-source distance - the VW stretched and became huge, about 15metres
long and high as a house - then it departed, plausibly enough.
My students have encountered the same when trying to reproduce a "Mousetrap"
game (a thing with rolling marbles that travel along little troughs, drop to
the next level and so on) in an auditorium - change the display radius, and the
sound of the speed of rolling and the change of angle seriously don't match.
So, one can't just treat things as 'point sources' (what is one of those,
exactly?) and movement has to take into account the display radius.
Still, a giant toilet flushing was fun to behold.
regards
ppl
Dr. Peter Lennox
Senior Fellow of the Higher Education Academy
Senior Lecturer in Perception
College of Arts
University of Derby
Tel: 01332 593155
________________________________________
From: Sursound [sursound-boun...@music.vt.edu] On Behalf Of Dave Malham
[dave.mal...@york.ac.uk]
Sent: 12 April 2015 09:12
To: Surround Sound discussion group
Subject: Re: [Sursound] Boids for Ambisonic Panning
Hi Ricky,
Boids has been around for a long time and I'm certain it's been
used quite a few times in electroacoustic compositions - in fact, I seem to
remember one of our students on the Music Technology course here at York
doing so. Trouble is, I'm darned if I can remember his or her name (which
will be no surprise to anyone who's been on that course - my apologies to
the person concerned if they are reading this :-). Your best bet would be
to look through the Proceedings of the ICMC from around '87 and maybe the
Computer Music Journal.
I'm not sure what you mean by "...difficult to scale in terms of
distance". Are you referring to the mapping of the notional distances in
the boid simulation to the things which we use perceptually to deduce the
distance of a sound source? That's opening up an interesting can of worms!
Do a search in the archives for "giant geese" to see the fun we had talking
(arguing) about it last time. A lot will depend on wether the sound sources
are "familiar" or not - we can easily tell that a thunder storm (or a jet) is
distant or nearby because we are familiar with them as "perceptual objects"
and can construe them within the acoustic space we are listening in but
with constructed sounds that we are not familiar with we are stuck with
"immediate" (and to some extent, unreliable) cues like direct to
reverberant ratios, the pattern of early reflections, HF rolloff and maybe
distortion (loud sounds have distortion which increases with distance). If
he's currently on the list, I suspect Peter Lennox will jump in here and
tell me I've got it all wrong :-).
Anyway, I'm sure much/all of this is old news for you but I had to have
something to occupy a Sunday morning whilst waiting for the croissants to
warm up ....
All the best....
Dave
On 11 April 2015 at 22:05, Ricky Graham <ri...@rickygraham.net> wrote:
> Hello,
>
> I use the boids algorithm to pan materials around a space. The Cartesian
> output number range per boid in space is difficult to scale in terms of
> distance; azimuth seems to be fairly intuitive and sounds correct to my
> ears.
>
> Do any of you have any similar experiences / advice on how best to
> approach distance when using boids?
>
> Best,
>
> Ricky
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--
As of 1st October 2012, I have retired from the University.
These are my own views and may or may not be shared by the University
Dave Malham
Honorary Fellow, Department of Music
The University of York
York YO10 5DD
UK
'Ambisonics - Component Imaging for Audio'
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