Rich:
I will be interested in hearing some examples from your setup.
What we might want to do is some standard test, like a person talking
directly on axis and then slowly moving 90 degrees to each side, talking all
the while and describing the location with respect to the axis. That way one
can determine the accuracy/quality of the spread of the stereo soundfield,
and one can also look at the phase changes of one channel with respect to
the other.
The Telinga barrier design does yield very nice stereo with the parabola
completely removed. Thus, the stereo soundfield is not dependent upon
reflections from the parabola.
For all parabolic mike setups (monaural or stereo), the sounds arriving
directly at the microphones will not be in phase with the same sounds
reflected off the parabola back to the microphone. For on-axis sounds, it is
assumed that on-axis reflected sound is so much louder than the direct
on-axis sound that the interaction between the two is insignificant in
practical terms.
Lang
I will try and put some examples up later today. I am packing for a
few days recording outing and trying to tie up some other ends.
I will also scope my examples to determine if they are mono
compatible. I believe mine are mono compatible but will double
check. I more often phase reverse one channel and sum to add
additional noise reduction than attempt to combine the two channels
which results in an overall drop in dish gain.
If you start your barrier at the mic diaphram and only project it
back away from the dish, then you will still have your cows in
stereo and try a 1" seperation of the diaphrams for your dish. For
mine I use 3".
You would then be using the whole dish for each microphone rather
than having reduced it to half. Also with separated mics your
targets at a distance will sound like wide separation stereo even
though they may be only 10 degrees separated. The down side is two
fold this way. One, the amplified stereo sounds will be fliped in
image from the off axis stereo sounds. Two, if you are slightly off
aim on a variable freq bird such as your grousebeak then the high
notes will be lower volume from the low notes which occationally
makes the location of the bird in image flutter from side to side.
Not better, just a different flavor.
Rich
--- In Lang Elliott <>
wrote:
> Yes. My setup is basically the same as used in the Telinga Stereo
Dat Mike.
>
> http://www.naturesound.com/telinga/telinga.html
>
> Rich, what is it you "hear". I believe that you prefer spaced
mikes with no
> barrier. Do you have any good examples for listening?
>
> Lang
>
> 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
>
>
>
> "Microphones are not ears,
> Loudspeakers are not birds,
> A listening room is not nature."
> Klas Strandberg
>
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> [Non-text portions of this message have been removed]
"Microphones are not ears,
Loudspeakers are not birds,
A listening room is not nature."
Klas Strandberg
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