<<I think that the distance between the elements is the main
engineered portion, IMO. You can have your mics at any angle as long
as the distance (17cm) is achieved. You can't officially call it ORTF
that way, but still. There is quite a bit of play in that number as
your mic elements are probably 1cm or larger in width. And the speed
of sound varies depending on factors. If it sounds good it is good.>>
The various stereo techniques for the most part were the result of
taste decisions made by different broadcast organizations in order to
arrive at consistent results regarding stereo width vs mono
compatibility when a variety of engineers were involved. The fact that
they all work, all involve some degree of compromise & all provide
slightly different stereo results tells us that there is no one
perfect or most accurate technique. And they are all variations along
a spectrum of possibilities. I find it best to think of the strictly
specified techniques as starting points, to be altered as needed by
each situation.
<<I'm not so sure what's so magical about 17cm, but it seems to make a
noticeable difference IMO. >>
It's the spacing between human ears, more or less, & thus provides a
reasonable compromise between stereo width & mono compatibility.
<< Even when the mics are parallel (0 degrees). Or you could play it
safe and keep the mic elements as close as possible so you can mix to
mono while still having a wide soundscape in stereo.>>
The chief disadvantage to this approach, i.e. mics as close as
possible, is a decided lack of stereo width. One of the main
attractions to the ORTF technique is a much wider panorama while still
maintaining an acceptable degree of mono compatibility.
<<I tend to want to zoom in on sources at a distance so I rarely get
past 90 degrees myself. Not that OMNI mics are supposed to be
directional, but once you start factoring in the rigging or the
landscape there is some directionality to them.>>
Actually all omni capsules tend toward directionality at higher
frequencies, irrespective of any boundaries.
Scott Fraser
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