By my ears it appears that you run a partition between the two mkh-
20's, correct?
Rich
--- In Lang Elliott <>
wrote:
> Re: Stereo Parbolic recording
>
> I've been doing lots of recording using my custom stereo Telinga
MKH20
> setup. Go to the address below to listen to a recording I made
last weekend.
> It features a Rose-breasted Grosbeak plus the sounds of some other
animals,
> big critters of some sort. Maybe someone in this group can tell me
what
> creature so rudely interrupted my grosbeak recording. Be sure to
listen
> using headphones so that you can fully appreciate the marvelous
stereo
> effect:
>
> http://www.naturesound.com/mp3/rbgroby.mp3
>
> Studying the waveforms of my various stereo parabolic recordings
on the
> computer, I've discovered the following important fact. Unless the
target
> bird is exactly focused, with the bird's song being identical
amplitude in
> both channels, there is often a resultant phase difference between
channels.
> This occurs even when the target bird is "slightly" off-axis.
>
> This can cause major problems when one desires a monaural
recording and sums
> the two channels to obtain it. Phase cancellations then reduce the
amplitude
> of the target bird's song, and may also result in other anomalies.
For this
> reason, it is not a good idea to mix the two channels to monaural.
It is
> better to choose the channel where the target bird is the loudest
and use it
> as your monaural source.
>
> This negates my earlier conclusion that the stereo parabolic setup
produces
> a monaural recording superior to that of a monaural parabola. This
is true
> in theory, but only if the target bird is perfectly focused and
there is no
> phase variation between the two channels. In actuality, it turns
out that
> this is rarely the case, unless the target bird is in direct view
and
> focusing becomes foolproof. When the bird is not seen and one
focuses the
> parabola "by ear", it seems to be the norm that it will end up
slightly off
> axis, with phase differences evident.
>
> It follows that if one chooses the loudest channel in a stereo
parabolic
> recording to produce a monaural version, then this will produce a
result
> that is somewhat inferior to that produced by a monaural parabolic
setup. I
> haven't tested this in a controlled situation, but I expect that
using only
> one channel will result in a loss of signal-to-noise of 3-5 db or
so. Maybe
> one of you tech-heads can tell me what would be expected in theory.
>
> I expect that the Telinga Stereo DAT mike exhibits the same
behavior as my
> custom setup. A quick preliminary test revealed that this is
indeed the case
> (I noticed similar phase differences between channels).
>
> In spite of this potential "problem", I am totally sold on stereo
parabolic
> recording. If you listen to the mp3 I've posted, using headphones,
then
> you'll hear why. The listening experience is far more pleasurable
that one
> has with mono. Off axis sounds come from their proper directions
and the
> sense of spaciousness is superb. Listening at home becomes a real
joy, and
> monitoring while recording in the field is much more exciting.
>
> Lang
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