John,
Yes, I also find it very strange that in all of my research of MS stereo mi=
c'ing techniques almost nothing is mentioned about stereo-image side swappi=
ng when using a super-cardioid mid. In fact, before trying it myself, the o=
nly thing I read about using a super-cardioid pattern for recording in MS w=
as that many people liked it for it's improved "focus" and off axis attenua=
tion (with the MKH50/30 combo being second in popularity to the MKH40/30).=
Being a recordist who does a ton of mono recordings for SFX purposes I thou=
ght I saw the purported value in this statement. But, it seems, the big mis=
take in my thinking (and I am curious about other's thinking on this topic =
as well) was that the Mid mic would continue to act like a forward facing m=
ic in a stereo MS setup, when it actually does NOT. When the Mid and Side s=
ignals are decoded into stereo the end result is IDENTICAL to an equivalent=
XY setup (shown very clearly with diagrams in this paper: http://www.ribbo=
nmics.com/pdf/technique.pdf) which means that the solo Mid super-cardioid m=
ic's off axis rejection is actually only helpful when listened to alone or =
when the MS stereo signal (decoded or not) is played back in mono.
It seems to me that in stereo recording you are basically nullifying the ad=
vantage of a super-cardioid's off axis rejection and are instead only givin=
g yourself: 1) smaller recording angles (as John stated in his example of a=
rubber band stretching), and 2) the potential for throwing rear lobe recor=
ded signals into the opposite stereo speaker during playback. Therefore, I =
really do not see any advantage of using a super-cardioid mic over a cardio=
id for coincident stereo recording.
I have been reading over the Manfred Hibbing "XY & MS Stereo Recording Tech=
niques" paper today and have been very impressed by the information it pres=
ents about these interchangeable coincident stereo setups. I have found som=
e very lucid quotes in regards to my original post:
(these are from the polar plot comparison section of the paper, looking at =
XY recording angles)
about Cardioid
"Due to the fact that cardioid microphones record sound from all directions=
in phase the audio recorded from the rear is not side inverted."
about Super-cardioid
"Supercardioid microphones invert the phase of any signal originating 120 d=
egrees or more off the microphone axis." Therefore, "At [XY recording] ang=
les below 120 degrees the signal recorded from the rear are side inverted a=
nd above 120 degrees they are not."
Very cool! So, as has already been mentioned in this thread (thank you Mich=
ael Raphael), it is the phase-inverted rear lobe of the super-cardioid micr=
ophone that is causing these stereo imaging problems. If I had a pair of MK=
H50's setup in an XY configuration and attempted an equivalent 360 degree w=
alk around test I would (it seems) experience the exact same thing.
-Justin
--- In "rock_scallop" <> w=
rote:
>
> Hi Justin,
> It is interesting, in the many times super-cardiod has been mentioned on =
this group as a possible option in an MS setup, the expected convolution of=
the stereo image has not really been explored until now.
>
> In your localization test, I heard something similar to what Jos=E9 descr=
ibed - though for the sake of interpreting the effect I will assume a theor=
etical L/R symmetry for this array configuration.
>
> The frontal stereo image becomes expanded, and the maximum perceived widt=
h occurs somewhere between 10 and 2 o'clock. At 11 to 1 o'clock the image s=
eems stretched from 60 degrees on location to around 90 degrees in playback=
. In this frontal wedge, the relative side to side localization of subjects=
might be fairly accurate. Though I think it is like stretching a rubber ba=
nd: as the width is expanded the depth becomes thinned. To the sides and =
back, including 10 and 2 o'clock and beyond the image becomes severely twis=
ted.
>
> All arrays distort the image in one way or another, so I am not discounti=
ng super-cardiod MS as useful technique for stereo nature recording - thoug=
h be extra careful with any content outside the angle of focus.
>
>
> John Hartog
> rockscallop.org
>
>
>
>
> --- In "freitojos" <josefreitas81@> wro=
te:
> >
> >
> > In my stereo speakers in a equilateral triangle 2mts 90=BA speakers. 1=
2 was 0=BA in front, 1 was 45=BA my right 2 35=BA right, 3 20=BA right 4 1=
0=BA right 5 10=BA left 6 was as 2 but far away 7 was 20=BA left 8 was 25=
=BA left 9 30=BA left 10 45=BA left and 11 12 0=BA in front.
> > I hope this helps,
> > Jos=E9
> >
> > --- In "ajustend" <ajustend@> wrote:
> > >
> > >
> > >
> > >
> > > Here is a link to the recording I made:
> > >
> > > http://soundcloud.com/justinmullens/ms-test-mkh30-50-handsofclock
> > >
> > > -Justin
> > >
> > > --- In "J. Mullens" <ajustend@> wro=
te:
> > > >
> > > > Hi, this is my first post to Nature Recordists.
> > > >
> > > > I have just added an MKH 30 to my collection in order to expand int=
o MS
> > > > recording and am experiencing very bad imaging (side swapping) with=
the
> > > > setup when the sound source is located in certain places behind the
> > > > microphone.
> > > >
> > > > To clarify, I am *not *trying to record a surround signal using a s=
tereo
> > > > mic setup, but I *am *interested in maintaining a correct left-righ=
t stereo
> > > > image. When I use an XY setup, or an XY mic like a BP4025, anything=
on the
> > > > left side of the mic (in front of it or behind) will playback out o=
f the
> > > > left speaker. Using the MKH30/50 combo this is not the case.
> > > >
> > > > Here is the test I conducted: Set the microphones up in the middle =
of an
> > > > open field so that I can walk in a full circle around it. I start d=
irectly
> > > > in front of the M/S setup, about 15-20 feet away, and walk in a clo=
ckwise
> > > > direction around mic calling out each position on the clock face. 1=
2 is
> > > > directly in front, 1, is to the right of that, 3 is directly to the=
right,
> > > > 6 is directly behind, 9 is directly to the left side, etc.
> > > >
> > > > Here's the problem, when I get to the 4 & 5 o'clock postions (rear =
right
> > > > side) the sound source swap sides and sounds like it is coming from=
front
> > > > left. And the exact opposite happens to the 7 & 8 o'clock positions
> > > > sounding like they are coming from the front right.
> > > >
> > > > Again, any source originating in the 180 degree arc in front of the=
setup
> > > > performs beautifully and the stereo image is perfect. It only happe=
ns to
> > > > sounds coming from behind the mics, and if a sound source is making=
a
> > > > constant tone you can actually hear it jump diagonally across from =
one side
> > > > of the stereo field to the other as it enters these rear right & le=
ft areas.
> > > >
> > > >
> > > > After asking around it has come to my attention that the closer you=
r Mid
> > > > mic is to a pressure-gradient mic (figure 8 polar pattern), the mor=
e of a
> > > > rear lobe you have, and thus the more chance you have of that rear =
lobe
> > > > picking up sound in the opposite channel. This definitely explains =
how, and
> > > > why, I could be experiencing side swapping.
> > > >
> > > > Since I've never used an MS setup with a pure cardioid mic I am won=
dering
> > > > if the same thing happens... For those using a Sennheiser 30/40 MS=
setup:
> > > > does this happen? Do you have side swapping in the 4-5 o'clock and =
7-8
> > > > o'clock positions?
> > > >
> > > > Nature recording is, for me, one of the areas where a really accura=
te
> > > > stereo image in a 360 degree circle around my recording location is
> > > > critical. I am always pointing my mics at the source I am recording=
, but
> > > > having sounds behind the mic appearing in opposite channel is just =
weird.
> > > > How do the MS recordists on this forum deal with this?
> > > >
> > > > Thanks!
> > > >
> > > > -Justin
> > > >
> > > >
> > > >
> > >
> >
>
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