For ambient soundfields a mono signal can be achieved simply by using
only one channel. Then you have no worries about phase cancellation.
There are also volumes written on which stereo setups work best when
played back through headphones or speakers.
For my ambient recording I find I get the richer soundfield from a
ORTF array than a M-S arrangement. I have yet to experiment with a
spaced array, as Walt said it can be difficult to setup/transport in
the field.
--greg
--- In Walter Knapp <>
wrote:
> tatiana irvine wrote:
> > Hi Everyone,
> >
> > I just joined this list and I'm going to jump right in with a
question. I am
> > looking for advice about just how far to space omnis when
recording stereo
> > atmospheres in nature (as in 2 omnis on a stereo bar, not "binaural").
> >
> > What results has anyone out there gotten with different distances?
I spoke
> > to an engineer for National Geographic's "Radio Expeditions", and he
> > recommended 14 inches- is this an arbitrary style thing, or is it
necessary
> > to space them that far apart to get enough seperation to make up
for the
> > lack of a human head between them?
> >
> > I have only used these omnis for recording music, which is a bit of a
> > different bag due to such a strong primary sound source and
associated phase
> > concerns-
> >
> > Yes, I know....use my ears....just curious about approaches...
>
> If you wish to try omni's without a barrier, then the rules are really
> no different than in music. Except your soundstage may be hundreds of
> yards wide, the "room" acoustics is entirely unpredictable and uneven,
> and the performers do no retakes and perform from where they please,
not
> in standard arrangements.
>
> Phase concerns are the same. Pretty much you should assume your
> recording will not mix to mono well.
>
> I expect the National Geographic engineer may have been thinking about
> mic setups for a narrator or close mic of a individual calling bird.
> Sounds way too close together to get much with a couple omni's as
far as
> the overall soundfield goes. I expect the "stereo" you will get from
> that spacing will sound more mono than stereo. The National Geographic
> engineer has to constantly be aware of how his sound will mix to mono,
> so probably compromises.
>
> Most of the nature shows I've seen when they had a mic in the
picture it
> was on a fairly short boom, and was a standard zeppelin with
windjammer,
> so the mic was hidden. But, about all that fits in that for stereo
would
> be a MS setup. I expect in a lot of it what's inside is a MKH-416
> shotgun mic or the equivalent, ie mono.
>
> My guess is that if you are trying to record a soundfield, that you can
> forget the bar unless it's a long one. 2 meters or more may be where
you
> end up. And you may find that a high placement will work best, 15' or
> more up, to avoid the local ground reflections. You really will have to
> just try and listen. There are no rules that work universally. Nature
> recordists are really, for the most part, just getting into stereo,
many
> still record with single mono mics. So we don't have hard and fast
rules
> worked out like music has.
>
> One other technique to consider that I know some music pros use. Do
> Pseudo Stereo. The description of how one of those folks sets up is
> interesting. He sticks a finger in one ear and wanders around listening
> for a "sweet spot" for the other ear. He places a mic there, then
sticks
> his finger in the other ear and repeats the process. It's Pseudo Stereo
> in that you are not trying to accurately portray the soundfield, but
are
> trying for a listenable soundfield. Obviously this route could be
> extended to many more mics and then mixed to sound good. And depends
> very highly on the listening abilities of the person setting it up.
>
> My own suggestion of a good thing to do with a pair of omnis for nature
> recording is to go with a barrier and reduce the spacing to head width.
> This also improves the portability of the setup, a real
consideration in
> nature recording.
>
> The SASS enclosure, fitted with good omni's does a excellent job. It's
> part head spaced omni, and part boundary mic. It has some binaural
> characteristics, but works well with speakers too. If you have the
> omni's then the parts from crown to do it don't cost a lot. Some
> machining is required to mount the mics. Here's what a couple of them I
> made look like:
> http://frogrecordist.home.mindspring.com/docs/sass_mkh110.html
> http://frogrecordist.home.mindspring.com/docs/sass_mkh-20.html
> And here's what I've gotten in my first tries, the subjects are frogs:
> http://loscan.home.mindspring.com/B.SASS.MKH110.mp3
> http://loscan.home.mindspring.com/B.SASS.MKH20.mp3
> http://loscan.home.mindspring.com/S.SASS.MKH110.mp3
> http://loscan.home.mindspring.com/S.SASS.MKH20.mp3
> http://loscan.home.mindspring.com/SP.SASS.MKH110.mp3
> http://loscan.home.mindspring.com/SP.SASS.MKH20.mp3
>
> Another spaced system to try is the Jecklin Disk. Here the omni mics
are
> spaced head width, 165mm, with a solid disk of 280mm diameter between
> them that's covered with sound absorbing material. Anyway, that's the
> original dimensions.
>
> I've also seen some homemade versions of the Schoeps sphere. Usually
> made from a toy ball of suitable dimensions. I've not heard of any
> nature recordist trying this one. The foam block system Rich Peet has
> would be somewhat similar. When you get into this stuff the analysis of
> the soundfield pickup from the mics is complex. Usually just listen, it
> works or does not, don't get into why too much.
>
> Walt
>
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