Klas:
I wasn't aware that you use 4 electrets per channel in your Stereo DAT mic.
I'd have to remove the windscreen to see the mikes and I didn't dare do
that.
In any event, it is clear that my test results were real and that they are
easily explained. Given this result, I see little reason to record in
monaural except for the following reasons:
1. If one can't afford two good mikes, or if one is not willing to build or
buy a stereo parabolic setup.
2. When trying to record heard but unseen birds, a monaural parabola is
easier to focus than a stereo parabola. In field situations, one often find=
s
the exact location of an unseen bird by pointing the parabola in its genera=
l
direction and then waving it left/right or up/down as the bird sings,
listening over headphones for a sudden peak in loudness, which happens when
the bird is in good focus. I have focused on many an unseen bird using this
technique. With the stereo parabola, it is more difficult to find the bird
using this technique.
Lang
Lang, Raimund, this is why I use 4 electrets in parallell (per channel)
with the stereo Datmic. 2 mics lower the noise by 3 db, 4 mics by 6 db. As
all 4 mics are so close to oneanother, you won't get audible phase losses.
Klas.
At 23:55 2004-04-11, you wrote:
>Lang,
>
>I think that your measurement results are indeed very precise and nicely
>confirm a basic law in signal processing, that says that independent noise
>signals add geometrically (sum =3D sqrt(a*a+b*b). If the two signals have
>the same
>amplitude (e.g. 1 V), then the sum of two signals is 1.41 V (the square ro=
ot
>of 2.0 V) and not 2.0 V as one would perhaps expect. In other words, the
>resulting noise level drops by the factor 0.7 ( =3D 1.41 / 2.0), which exa=
ctly
>corresponds to -3 dB. The fact that you really got that 3dB difference is
>also a
>proof for the good acoustic isolation between the two mikes. The two mikes
>pick up noise from different sources that are not correlated to each other=
.
>
>The same principle applies to the inherent noise sources within the record=
er
>(the two preamplifiers and AD converters). Therefore, splitting a monoaura=
l
>signal to a stereo input will also decrease the self-noise level (when the
>two channels are finally mixed together). However, I guess, that this bene=
fit
>can be almost neglected because the self-noise level of a state-of-the-art
>recorder is usually small compared to that of the microphone.
>
>Raimund
>
>
> > Re: Stereo Parabola versus Monaural Parabola
> >
> > This morning I did a fairly thorough comparison of the output of my ste=
reo
> > parabolic setup and the output of my monaural parabolic setup.
> >
> > My stereo setup was my Telinga Parabola outfitted with two Senheisser M=
KH
> > 20
> > omni mikes placed to each side of a plastic barrier just like the desig=
n
> > that Klas uses in his DAT Stereo mike. I provided pics of my design som=
e
> > months back. For those new to our group, the pics may be found here:
> >
> > http://www.naturesound.com/telinga/telinga.html
> >
> > My monuaral setup was a Telinga Parabola with a Telinga Universal Mike
> > Mount
> > outfitted with a single Senheisser MKH 20 omni mike.
> >
> > My question was whether or not a stereo recording obtained from my ster=
eo
> > parabola has a signal-to-noise ratio that is comparable to that of a
> > monaural recording from my monaural parabola.
> >
> > So here's what I did:
> >
> > To produce a standard signal for my test, I chose my best recording of =
a
> > winter wren and put a single song on a CD. I used noise reduction to
> > reduce
> > the background of this recording to almost nothing. I went to a quiet
> > woodland setting near Ithaca, placed my portable CD recorder on the gro=
und
> > and fed the output to a small speaker, using the repeat function of the
> > player so that the song would play over and over again, with a pause of
> > about five seconds in between. There was a very gentle breeze, insuring
> > that
> > the ambience heard behind my test recordings would be the slight whoosh=
y
> > or
> > hissy sound of the gentle breeze, not the mike noise floor, and not the
> > ambience from the CD recording itself.
> >
> > Using the two different setups (stereo parabola and monaural parabola),=
I
> > recorded the winter wren song and adjusted my recorder in both instance=
s
> > so
> > that the peak record volume was -3b.
> >
> > After making recordings using both setups, I returned to my studio and
> > inputted the test recordings into my computer.
> >
> > Using PEAK audio editing software, I first chose a song recorded with t=
he
> > stereo setup plus some of the gentle breeze ambience that accompanied i=
t.
> > I
> > then created a monaural soundfile by mixing the two tracks together. Th=
en
> > I
> > normalized this recording so that the song peaked exactly at -3db. Then=
I
> > deleted the song itself, leaving about five seconds of the gentle breez=
e
> > ambience.
> >
> > I then processed a monaural recording using exactly the same procedure.=
Be
> > aware that the monaural recording was made to two tracks using a Y-cabl=
e
> > that splits the output of the monaural Telinga into two inputs for the =
DAT
> > recorder. So first I mixed the two tracks to create a monaural track in
> > PEAK. Then I normalized to -3b. Next I removed the song itself, leaving
> > about five seconds of ambience.
> >
> > Then I made a new soundfile in PEAK, which included both examples of th=
e
> > ambience, one following the other with a fraction of a second of silenc=
e
> > in
> > between.
> >
> > Finally, I compared the loudness of these two samples of ambience with =
the
> > assumption that this would give me an accurate measure of the
> > signal-to-noise capability of the two parabola setups when they are use=
d
> > to
> > create monaural recordings ("noise" here refers to the level of the
> > ambience, not mike noise).
> >
> > The results surprised me. The ambience from the processed stereo record=
ing
> > was exactly 3 db quieter than the ambience from the monaural recording!=
! I
> > tried several examples and got exactly the same result each time.
> >
> > This is good news because it means that recording in stereo using Klas'=
s
> > design yields a two-track recording that can be used to produce a monau=
ral
> > recording that is every bit as good as what I can get using a standard
> > monaural parabolic setup. In fact, the result was 3 db better in terms =
of
> > signal-to-noise.
> >
> > I had actually expected the opposite: that recording in stereo would
> > produce
> > a nice-sounding result, but at the expense of some signal-to-noise in
> > comparison to a monaural recording (as long as both are made using the
> > same
> > parabolic reflector, the same microphone type, and Klas's stereo and
> > monaural types of design).
> >
> > What do you tech-heads think of this result? Does this make any sense?
> > Don't
> > you agree this is good news?
> >
> > One question I have is whether or not splitting the monaural parabola
> > output
> > to two channels for DAT recording is influencing the results. I know th=
at
> > this could result in a slight increase in the noise floor created by th=
e
> > mike, but it shouldn't affect the level of the ambience which accompani=
es
> > the bird song. Using my monaural setup, I typically record to two track=
s
> > because it sounds better when monitoring (my recorder only allows for
> > stereo
> > monitoring), and because it provides two tracks just in case there's a
> > glitch in one. Anyway, when the two tracks are mixed back to one track =
in
> > the studio, the results should be the same as when only one track is
> > recorded from the parabola.
> >
> > Any thoughts about my test and my conclusions?
> >
> > Lang
> >
> >
> > "Microphones are not ears,
> > Loudspeakers are not birds,
> > A listening room is not nature."
> > Klas Strandberg
> > Yahoo! Groups Links
> >
> >
> >
> >
> >
>
>--
>NEU : GMX Internet.FreeDSL
>Ab sofort DSL-Tarif ohne Grundgeb=FChr: http://www.gmx.net/info
>
>
>
>
>"Microphones are not ears,
>Loudspeakers are not birds,
>A listening room is not nature."
>Klas Strandberg
>Yahoo! Groups Links
>
>
>
>
Telinga Microphones, Botarbo,
S-748 96 Tobo, Sweden.
Phone & fax int + 295 310 01
email:
"Microphones are not ears,
Loudspeakers are not birds,
A listening room is not nature."
Klas Strandberg
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