SableTones wrote:In respect of the omni tracks my Voxengo Span plug in Corellation meter shows signal predominantly around centre/zero when left right tracks panned hard left/right.
As it should. There will be almost no correlation between the signals from spaced omnis panned hard L/R, and no correlation is represented by 0 in the middle of a standard correlation meter.
when i centre both tracks....the Voxengo meter is solidly at 1.0 hard right.
Again, exactly as it should. If you centre the pans you have dual-mono, and a mono signal is inherently fully correlated, which is indicated by the 1 at the right end (or top) of the meter.
For completeness, the -1 on the meter indicates correlated but opposite polarity (ie something strongly out of phase).
(nb: i did this to compare effects of the two mic configurations)
I would expect the ORTF array to be more strongly correlated than the spaced omnis, so it would probably give a reading closer to the 1 end of the scale, the precise correlation value depending on the acoustics of the room and the size and position of the sources relative to the array.
This is basic meter interpretation 101. I've not seen the Voxengo manual, but the correlation meter has been around for many decades and is thoroughly described in countless relevant books and websites.
In brief, if the two inputs to the meter are identical -- dual mono -- they are 'fully correlated' and so the meter shows +1. If the two signals are completely different, they are 'fully decorrelated' and you get a reading of zero. In the specific case of a stereo signal, if the two channels are very different to each other, as they tend to be with widely spaced mics, you have the widest possible stereo image.
So in crude terms, a correlation meter reading of +1 means (dual) mono, and a reading of 0 means ultimate-wide stereo. So normal correlation meter readings for conventional stereo material will fluctuate between +1 and 0.
As I said earlier, though, if the two channels are identical but in opposite polarities the meter shows -1, and in fact any amount of out-of-phasiness in the stereo signals will kick the meter into its negative half between 0 and -1. Any reading in this half indicates a reduced degree of mono compatibility: something will get lost (or attenuated) when you listen in mono!
Some correlation meters are coloured green in the positive half, and red in the negative half to emphasise the compatibility risk associated with negative excursions!
Hope that helps.
H
