SPATIALIZATION (MULTI SPEAKER)
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SPATIALIZATION (MULTI SPEAKER)
2. Standard, official 5.1 setup
3. 'Octophonie'
4. GRM-like setups
5. Motus-like setups
6. Ircam Spat-like setups
7. More...
1. DEFINITION
There is a fundamental difference between stereo and multi-speaker spatialization.
In stereo spatialization, the image, called "virtual image", is behind the speakers :
The speakers form a window through which we look at the virtual image.
In multi-speaker spatialization, the issue is totally different ; for example here is a possible setup :
The notion of virtual image is, mostly, abandoned, and replaced by other elements of vocabulary.
One exception : the official 5.1 or 7.1 multi speaker setups, which are often used as an extension of the standard stereo setup, still use the virtual image notion and techniques.
2. STANDARD, OFFICAL 5.1 SETUP
The official 5.1 specifications :
5.1 is based on stereo
Using L&R speakers only, one has a classic stereo setup.
Virtual image techniques can be used between the L & R speakers, and, to a lesser extent, between the R & Rs, L & Ls speakers.Academically, Ls and Rs are mostly used for ambiences, out of phase informations. Two reasons for that :
- in the field, too many rear effects are considered vulgar !
- Dolby Surround filiation : in the dolby surround setup (5 speakers decoded from stereo), out of phase and only out of phase informations were decoded to the rear speakersUses : cinema, domestic.
In theaters, it works usually very well. In private homes... well, very few people go to all the trouble to have a "specification compliant" surround setup !
3. 'OCTOPHONIE'
In the field of contemporary music, this is a largely used setup :
From an abstract & intellectual point of view, this setup is very satisfying - in fact it strongly recalls of the visu-audition phenomenon.
This setup is mainly used in live situations.
Important drawbacks though :
1. doesn't adapt to the room acoustics
2. people far from the center lose a lot of spatialization informationFurthermore, it's a one dimensional setup : the only spatialization parameter that can be used is "from where the sound comes out" !
And no notion of distance can be included in the "where".
4. GRM-LIKE SETUPS
Largely used for the GRM concerts.
A stage, an audience, and speakers on stage that replace musicians.
Note that the audience is separated from the speakers : it's a fully frontal setup.
Speakers are meant to be of various sorts.Pros :
- adapts to the room acoustics
- multi dimensional: timbre (various speakers), position in space (L/R), distance
Cons :
- Fully frontal
- Usual stage/audience issues : people on the side, too close, too far.... have not as good an experience as people in the middleNote that the virtual space we had in stereo can be recreated with the use of different speakers.
5. MOTUS-LIKE SETUPS
A very good use of this kind of setups is used by the Motus group in France & Japan.
The audience and the speakers are meddled. Speakers are meant to be of various kinds.
The setup is, from the start, asymetrical.
Each person in the audience will hear something different, and the performer will make it so that each person will hear something interesting.
Thus, each performance can be a different experience : just move to the other side of the room, and it doens't sound the same.Pros :
- the only setup to take full account of the room acoustics and thus adapt to any situation
- each person in the audience gets a fully interesting result
- highly multi dimensional : timbre, position, distance, even audience
"Cons" :
- not rooted in any tradition !
- doesn't look serious !
6. IRCAM SPAT-LIKE SETUPS
This is a bit different.
The Spat software suite processes the sound to be spatialized, and, supposedly, everything is made possible : any trajectory, any distance from the listener....
Also, the software suite is supposed to adapt itself to any speaker setup, in any room - in practice, I don't know...
Pros :
- scientific approach
- theoretically, endless possibility
Cons :
- scientific approach
- heavy, difficult to handle for a non trained musician
- forget about pristine signal path....
More : group diffentiation and space differentiation in sound projection