Re: On 8 speakers


Subject: Re: On 8 speakers
From: KEVIN AUSTIN (KAUSTIN@vax2.concordia.ca)
Date: Tue Jan 26 1999 - 04:32:10 EST


On multi-speaker systems, Chris Rolfe continued:

>I wrote the software for the system Darren and co. are using, so maybe a
>word or two here about design philosophy wouldn't be out of place.

>The user can specify angle placement for any given input. The speaker map
>is edited separately, the idea being that you might want to pan a sound
>from 10 degrees to 190 degrees, and not be worried about speaker location.
>Speaker maps are simple graphic documents that record the current venue
>speaker locations.

Is the panning done using amplitude, reverberation, low-pass filtering
and doppler?

[snip]

>The biggest trick is to get composers to work in 8 channels. We're all so
>used to reducing to stereo that we fail to compose in space. The greatest
>mistake I see is that composers tend to reduce everything to a "flying
>object", when in fact there are very few sounds that pan successfully. 8
>discrete channels are, however, a wonderful thing to hear.

I my experience, the "flying object" 'mistake', is one of the most
difficult to work with. It would appear to stem from the view that sound
behaves in ways similar to light, and speakers are treated as if they
were lights (or light sources). A simple example.

Given four speakers and four lights in a straight line ...

             L LC RC R

If the lights are turned on in the sequence: L - RC - LC - R, the eye
will follow the movement [start] L -> R -> L -> R.

When this is done with a mono source, the effect (in semi-reverberant
conditions) is more like: L -> a bit more to the center -> louder
[perhaps] -> a bit more to the right [but unlikely].

If the objective is for the audience to hear L -> R -> L -> R, then there
will be a problem. On the other hand, the audiences' perception and the
objectives / techniques of the composer may be largely unrelated ... but
that's another area.

Another common idea would be where (simplified), there are three
loudspeakers:

                     A
  
           1 2

The mono sound starts in 'A', and the composer designs a split trajectory:
at the same time, the source from 'A' goes to 1 and to 2. The visual
analogy is that the sound 'splits' apart. With a mono sound however, this
is not the result.

This is a problem that Eric Johnstone (at McGill) and I pondered long and
hard on when he was designing a touch sensitive CRT screen for sound
projection / diffusion around 1972-3. It was one thing to draw the line:
it was something else to make it mean anything. (At the time we were
working on a proposed 8-channel idea with the speakers situated as:

            A B

                    E F

                    G H

            C D

This was a reduced (and generalized) scheme that was used in the
'Spectraphonia' presentation space in 1969 / 70 / 71, designed (if I
understand correctly), partly by Paul Pedersen. (It was a 12 channel
system, with around 40 channels of lights.) This was also the speaker
configuration prefered by MetaMusic (the sound of three hands clapping),
from 1970-75.

Here at Concordia, we look forward to being able to audition the
application of Chris' package (Tue Feb 09), and comparing it to other 4
and 8 discrete channel pieces (Fri Feb 12).

Yves Daoust is hosting a three week workshop at the Conservatoire and I
am sure that much of interest will come from this work.

Best

Kevin
kaustin@vax2.concordia.ca



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