[LAU] inverting phase of one channel - bad idea?

[Fons Adriaensen]

On Tue, May 27, 2008 at 11:14:18AM +0200, Atte André Jensen wrote:

> A question came up on the chuck list today, regarding how to invert the 
> phase of one channel. The poster wanted to use this "trick" to widen the 
> width of the stereo image, and it sure does.

Bah, what you get is no stereo image at all, but some sort
of 'spatial soup'.
 
> However now I'm thinking if it's a good idea in the first place. Besides 
> loosing mono-compatibility, I have a gut feeling that audio treated this 
> way will become very uncomfortable or even annoying to listen to after a 
> while.

True.
 
> Does anyone have any thought about this? Should this "trick" simply be 
> avoided or are there situations where using it on some parts of a mix 
> would be ok (keeping in mind that the tracks in question will disappear 
> in mono)?

Just don't do it. 

What you can do on selected tracks is to pan a bit 'outside the 
speakers'. Normally if you pan e.g. hard right then L will be
zero, but you could make it negative. Most panners can't do this
but you get the same effect with

L' = R - a * L
R' = L - a * R

with 0 <= a <= 0.5.

Still not very good for mono compatibility, but if used with some
care, and on selected tracks, it works.

If you are listening with a normal stereo setup (angle between 
speakers = 60..90 degrees) and feel the need to this, then there
is probably something wrong with your mix, and that should be
solved first. Could be it's missing some early reflections.

If the purpose of all this is to get a wider stereo image from
e.g. speakers built into a monitor, then there are other methods,
like crosstalk cancellation. But these should be applied at the
listeners's end, not in the mix.

-- 
FA

Laboratorio di Acustica ed Elettroacustica
Parma, Italia

Lascia la spina, cogli la rosa.