> Have any of you seen this structure and if so, how are these signal sourc=
es positioned (i.e. is 90L/R on the right or on the left when looking down =
on it)? How are they recorded (I'm assuming 4 pairs of stereo mics)? And mo=
st importantly, how are they processed, edited and embedded into the mp4 fi=
le so that they are positionally correct?
Eric,
Have you seen
<http://en.wikipedia.org/wiki/Surround_sound>
The major problem with surroound sound, unlike surround video, is that we
don't have realistic narrow angle mics. With video the various picture
frames can be placed side by side giving a continuous surround image, but
with many directional mics you would have many overlaps and side, rear, top=
and bottom lobes which would muddle the sound image.
I would suggest the cleanest rig would be four coincident cardioids at righ=
t
angles or the equivalent of one omni and two fig-8 at right angles and
matrixed later into effectively four cardioids.
Hypercardioids would give narrower angles, but they are notoriously
frequency dependant off-axis and have rear lobes which are of varying phase=
with frequency so would be difficult to matrix out.
I have had some success with using short gunmics (MKH 416) for stereo and I=
get away with the multiple lobes in practice getting reasonably clean front=
,
left and right images in stereo, and I would probably try this type of rig=
for surround sound. Gunmics have the advantage of lower top and bottom
sensitivities.
So saying, any directional stereo rig will have very audible out of phase
component which can give the effect of diffuse rear sound, especially on
headphones. With four or eight directional mics, this cross-talk would
diminish the main directional images which would be masked to a greater or=
lesser degree by the out of phase sounds.
Cinema surround sound is produced from a large number of discrete tracks
each pan-potted to the appropriate speaker channel or channels, and also to=
height speakers to give a vertical sound image effect and also "rumble" bas=
s
speakers. The equivalent for wildlife recording would be to have widely
spaced stereo pairs, possibly in different locations, mixed to give a
combined surround effect.
David Brinicombe
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