A dipole configuration is also possible with matched omni's. Although the
diameter of the diaphragm will affect the point (phase) at which you can no
longer use the intensity difference for directionality. Basically the smaller
the better , but it could work with the MKH-8020's. Ive tested this with the
NT45-O capsules and had very limited success compared to 10mm omni electrets,
the NT4's fixed mic angles didnt help matters there. check the link later in
this message..
Basic configuration:
Set both mics facing forwards and right next to each other, rubber band both if
possible but keep the band away from the front. Record your environment, or a
test room / location. -It will sound very mono due to the coincident mics.
In the DAW:
MS matrix, LR -> MS
In-between these add EQ to boost the left channel (side's) low frequency
response, depends on the mic but at least 10-20dB is needed to around 800hz. -
try to match it with the right if possible and tweak for width.
Another MS matrix MS -> LR
This is intensity shuffling, the chain of EQ may also need some pre-EQ for each
mic if they are not exactly matched, or due to recorder amplifiers being a few
tenths of a dB offset.
This will realize a figure 8 from the (L Omni - R Omni) and a omni from the sum
of both. You can then mix various amounts of the side to set the width of the
recording similar to an MS mic, yet your starting with a very quiet pair of
excellent omni's. -The only downside is that the coverage pattern will be
focused towards the front and perhaps the side coverage will not be as good as
a dedicated figure 8 due to the on axis vs off axis response difference of the
omni's.
My experiment using the NT4 and NT45-O capsules can be found here:-
http://www.urlme.net/blog/?p=1429
And also related using small electrets - this page also shows the EQ needed.
http://www.urlme.net/blog/?p=1277
BR
Mike.
--- In "Avocet" <> wrote:
>
> > The rig will mainly be used for recording urban and interior
> > soundscapes.
>
> Matthias,
>
> I'm researching various stereo techniques and putting together a guide
> to stereo field recording and am amazed by the variety of techniques
> used. Your starting point is a pair of excellent omni mics and the
> first thing to consider is how to make them directional. One rig is
> effectively a dummy head in many disguises which uses phase and time
> differences to get directional information, and the wide range of
> these devices rather demonstrates that the ideal format has not yet
> been achieved. I'm also generalising when I say that binaural
> recording like this is best listened to on headphones as you don't get
> a consistent phase relatioship from loudspeakers indoors. I'm quoting
> the BBC on this and they have transmitted several dramas and
> documentaries on dummy head binaural stereo.
>
> My advise would be to experiment and hopefully come up with new
> techniques. One thing I will predict is that any rig based on omnis
> will finish up with a 360 degree sound object source and give a 180
> degree sound image. However with binaural it is sometimes possible to
> distinguish between front and back so that may be a challenge to take
> up.
>
> The immediate way to make an omni mic directional is to use a baffle,
> and the low frequency directional response will be dependant on the
> size of the baffle compared with the wavelength. Roughly a 440 Hz
> frequency (concert pitch "A") has a 770 mm (30 inch) wavelength so
> that's a starting point. It should still work down to 400 mm or so.
> Forget parabolas - they are too directional for stereo imaging.
>
> There is some variation on defining the barrier effect, but I used
> this professionally for many years. Sound "sticks" to a surface and a
> mic, any mic, gets more directional along the surface when the mic is
> laid hard against it. You don't need any foam "mice". I would suggest
> trying taping the mics either side of a large piece of plywood or
> rigid plastic sheet and seeing what that sounds like. Outdoors you'll
> need some open cell foam to act as a windgag, but one great advantage
> of omnis is that they are much less sensitive to wind and handling
> noise.
>
> I've done a little experimenting with two boards at right angles with
> a central partition forming a pair of right angled horns. Omni mics
> are mounted at the throat of each horn. I got a surprisingly good
> stereo separation at mid to high frequencies and produces a good
> separation between front and back.
>
> You could also go back to Blumlein's original omni pair and experiment
> with the spacing. He never used the so called "blumlein pair" of
> fig-8's as he didn't have any. :-) However, his spaced pair principle
> produced the first ever stereo and is still used as part of a surround
> sound orchestral mix. Have fun. :-)
>
> David
>
> David Brinicombe
> North Devon, UK
> Cogito cogito ergo cogito sum - Ambrose Bierce
>
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