Whether
you record live or in the studio, stereo recording can heighten
the realism of your productions because simply put, we humans
have two ears, so a stereo recording sounds more natural to us
than mono. It's therefore pretty obvious that most stereo-miking
setups grew out of attempts to approximate the positioning and
functioning of our ears and over the years there have been a number
of interesting stereo microphone configurations developed, all
aiming to give the listener a realistic representation of the
sound environment in front of them. As with everything some are
more realistic than others, though of course sometimes its actually
preferable to be less realistic and more flattering as nowhere
is the room or location more important in shaping the sound. There
are numerous forums where people will argue into oblivion about
their preferred method and how every other set up is flawed but
pragmatically which set up I favour on the day is down to the
quality of the sound source and the room. I honestly feel that
the forum experts should get out and do some more recording instead
of talking about it. To start stereo recording you will need a
pair of microphones to represent your left and right ears and
the type of mics and their relative positions have led to 5 main
stereo recording configurations, each with strengths and weaknesses.
The first and most obvious stereo recording set up is an XY configuration
where a coincident pair of cardioid microphones are positioned
so that their capsules are as close to each other as possible
without touching. The angle between the capsules (called the mutual
angle) is usually set between 90 and 135 degrees, with the greater
angles creating a wider stereo picture. Directional, cardioid
microphones are most sensitive to sound coming from directly in
front of the capsules (on axis) and are less sensitive to off-axis
sound. In other words, the microphone "hears" lots of
sound coming from the front and much less from the sides. Therefore,
sound sources positioned in the centre of the angle between the
two mics will appear in the centre of the stereo field, whereas
sources off to one side or the other will appear more on-axis
to one microphone and thus will be reproduced louder on that side.
The XY setup generally gives you a workable but narrower, more
focused stereo image than other stereo-miking techniques and there
is often a 3 dB drop in the centre of the image as the centre
sound information is hitting both mics off-axis. I have had some
pretty successful results with a crossed pair of Rode NT5s recording
small choirs and instrumental groups and you certainly can get
a convincing stereo picture but it's only when you compare it
to other techniques that you feel its perhaps a bit pinched or
restricted. On the plus side any one can now afford to buy a pair
of decent quality condenser mics and you can either use two mic
stands or fit them easily onto a stereo bar on one stand. Rode
have taken the idea to its logical conclusion and produced the
NT4 mic which has the two capsules engineered at 90 degrees and
mounted on a single mic body. It is really good value and very
popular particularly as a stereo camera mic. When you're recording
multiple instruments, you can widen the stereo spread by arranging
the players in a semicircle around the XY pair and XY pairs also
work well for close-miking solo instruments particularly the acoustic
guitar and piano.
Developments on the coincident XY theme have produced a number
of near coincident techniques where a pair of
cardioid mics are slightly spaced apart to create a wider more
engaging stereo picture and perhaps the most effective is the
ORTF configuration developed by French radio
(Office de Radiodiffusion-Télévision Française)
in which a pair of cardioid mics are angled at 110 degrees apart
with 6.69 inches between the capsules (the average distance between
your ears) in an attempt to mimic human hearing. I always prefer
the sound of ORTF over straight XY and have a stereo bar set up
with clips at the correct angles so that I can just clip in a
pair of NT5s or more recently Hebden Sound 3020s. The great advantage
for me with this system is that if you have a room that isn't
particularly nice sounding you don't want to capture a lot of
it and I am always happier to get a tight stereo picture and add
some reverb back in the studio. (That strange sound you might
hear will be the gasps of the purist nerds)
Another near coincident set up is the NOS (Nederlandse
Omroep Stichting=Holland Radio) Stereo Technique which uses
two cardioid microphones spaced 30 cm apart and angled at 90°
to create the stereo image. I have tried NOS a few times but one
of the characteristics is if used at larger distances to the sound
source it loses the low frequencies due to the nature of pressure
gradient microphones and the influence of the proximity on these
type of microphones. However close in on something like a piano
the NOS technique can sound pretty good. Try it against ORTF and
see which you prefer.
