MS stereo imaging problems with MKH30/50 combo - Sounds are swapping sides behind mic

[aracu]

Originally Posted by OzGizmo

The other sort of fig 8 mics have dual diagrams in the mic and actually have 2 positive sides (which is the standard modern configuration).
I can recall some tests a work colleague and I did many years ago on some Neumann U87, TLM170 & KM88 mics with a fig 8 option, a phase 'blip' tester was used to identify the front and back of the mics and to our surprise both sides were 'in phase'.

The fig-8 polar pattern needs to have the back out of phase with the front to cancel sound coming from the sides. In that sense it is the most
directional pattern. There may have been an error with the testing procedure.

[aracu]

Originally Posted by leddy

I would take issue with the word "usable" with any mid-side ratio that causes it to not have an equivalent pair of coincident mics.

What is usable or not cannot be entirely pre-determined by or limited to a theory. Theory is a perfect model created by thought and tradition, a good starting point.

[leddy]

Originally Posted by apple-q

+1

Almost all of the SDC 8-mics are single diaphragm mics. (I actually don't know of any "pseudo-8-mic" in the SDC-segment but maybe there are a few.)

I've got a nice pair of KM86's (back to back KM84 capsules - which leaves about an inch between the front and back).

[leddy]

Originally Posted by aracu

What is usable or not cannot be entirely pre-determined by or limited to a theory. Theory is a perfect model created by thought and tradition, a good starting point.

Are you taking issue with MS = a conventional pair of mics?

I'm pretty sure Blumlein's patent assumes equal gain between the mid and side mics. Regardless, you can't use something outside of its intended use and use that experience to diminish its value within its intended use.

I can crank up the side mic gain until it's a phasey mess. Not sure that's what Blumlein had in mind. For that matter, I can use my MKH30 as a hammer...

[Rolo 46]

Originally Posted by David Rick

John, a rear channel swap can happen even with a cardioid mid. This is clearly documented in the Hibbing paper I referenced earlier. At the time of publication, Manfred Hibbing was working for Sennheiser, so you have no excuse!

As Larry Eddy mentioned earlier, it's because every M/S pair (and relative gain setting) transforms to an equivalent pair of coincident microphones. If those equivalent mics have rear lobes, then you get a channel swap at some positions in the rear. With a hypercardiod mid mic, the channel swap happens at lower levels of side mic gain than with a cardioid mid. With an omni mid, it never happens; in that case the front and rear sound stage mappings are always identical.

David L. Rick
Seventh String Recording

David
I have Hibbings 'XY and MS stereo recording techniques'.
Published by Sennheiser 06/91
He states:

MS Cardioid.
If a cardioid M microphone is used there is no rear recording area.
All sounds from the directions outside the recording angle are recorded as ambiophonic signals
If the S level is around 0dB the recording angle changes at a rate of 10 degrees/dB.

[aracu]

With a cardioid mid, what is recorded behind the mic is more reversed than with an omni mid (no reversal), but less reversed than with a fig-8 mid
(complete reversal).

[aJustEnd]

Originally Posted by Rolo 46

David
I have Hibbings 'XY and MS stereo recording techniques'.
Published by Sennheiser 06/91
He states:

MS Cardioid.
If a cardioid M microphone is used there is no rear recording area.
All sounds from the directions outside the recording angle are recorded as ambiophonic signals
If the S level is around 0dB the recording angle changes at a rate of 10 degrees/dB.

I'm not familiar with the term ambiophonic used here. Can you translate for me, please?

"All sounds from the directions outside of the recording angle are recorded as _________"?

-Justin

[John Willett]

Originally Posted by apple-q

+1

Almost all of the SDC 8-mics are single diaphragm mics. (I actually don't know of any "pseudo-8-mic" in the SDC-segment but maybe there are a few.)
The 2-diaphragm 8-mics are usually the dual diaphragm LDC (U87 etc.)

The fig-8 in the Sennheiser MKH 418S is dual diaphragm.

Also, the MKH 80, 800 and 800 TWIN are all dual diaphragm. These have the same 16mm diameter diaphragm as the MKH 20/30/40 series and MKH 8000 series.

[aracu]

Are you sure the Senn 800 diaphragm is not larger than the 8000 series diaphragms?

[John Willett]

Originally Posted by aracu

Are you sure the Senn 800 diaphragm is not larger than the 8000 series diaphragms?

Pretty certain.

The MKH 20/30/40 series definitely had a 16mm diaphragm and I'm pretty sure the MKH 80 had as well.

The MKH 800 was an extended frequency version of the 80.

The MKH 8000 series definitely have the same 16mm diameter diaphragm as the 20/30/40 series.

The original series had a screwed capsule, which increased its diameter, the 8000 series has a glued capsule that keeps the overall diameter extremely small so it fits into the 19mm diameter housing.

So, although the 8000 series is 6mm smaller in diameter than the 20/30/40 series, the capsule diaphragm diameter is the same.

[aracu]

The capsule of the Sennheiser 800 is wider than the diameter of a 8000 series housing by about an 8th of an inch. It's possible that the diaphragm
is narrower than the capsule though.

[John Willett]

Originally Posted by aracu

The capsule of the Sennheiser 800 is wider than the diameter of a 8000 series housing by about an 8th of an inch. It's possible that the diaphragm
is narrower than the capsule though.

The MKH 8000 has a 16mm diaphragm in a 19mm housing - the capsule is glued.

The MKH 800 has a screwed diaphragm (see picture) that has screws all the way round the outside, so it's much larger in diameter than the MKH 8000 capsule, even though the active diaphragm is the same size.

I hope this explains it OK.

[Yannick]

I am always amazed how threads about MS stereo always end up with completely faulty and useless opinions intertwined with magnificent, hard to find information.

To the original poster: I would just study the MS setup a bit more, it is clear you do not fully grasp the way it works, and how important the choice of M mic is (directionality).

One could also post something among these lines: AB stereo imaging problems with two xbrand omnis - sounds are jumping from L to R mic when walking around. (with an AB array spaced 2m apart).

As such, every known stereo setup is flawed in at least one aspect. It is always good to know those limitations.

If only that Sennheiser document would come online again, I have two hard copies in my archives, no pdf I am afraid.

[Rolo 46]

Originally Posted by aJustEnd

I'm not familiar with the term ambiophonic used here. Can you translate for me, please?

"All sounds from the directions outside of the recording angle are recorded as _________"?

-Justin

Technical German can be a problem for mere Anglo Saxons
'Lost in translation' is the phrase
If only we had the use of Ms Johansson

[John Willett]

Originally Posted by Yannick

If only that Sennheiser document would come online again, I have two hard copies in my archives, no pdf I am afraid.

I don't think it was ever on-line.

I have asked my contact at Sennheiser Germany to let me have a pdf of it (I have lost my copy, unfortunately).

I anyone wants a copy send me a PM with your e-mail address and I'll send it on if and when I get it.

[John Willett]

Good News!

I have now got a PDF copy of Manfred's MS & XY paper from Manfred himself.

It was only in printed form and he scanned it for me (I actually have a copy in the original German as well as the English version).

So - if anyone wants a copy please send me a PM and make sure you include an e-mail address for me to send it to.

And if you want a copy of the new "MKH Story", I have that on PDF as well.

[aJustEnd]

John, thank you for posting this paper, and David thank you again for recommending it. What a great read!

As I have been reading over the Manfred Hibbing "XY & MS Stereo Recording Techniques" paper today it has really helped solidify many of the reply's to my original question. The visuals of the polar patterns as they are used to compare the interchangeable coincident stereo XY & MS techniques has been very enlightening. It has allowed me to more fully understand and internalize the capabilities of MS recording. In that regard, I wanted to write back to follow up on my discoveries as my journey into MS recording continues.

I have found some very nice quotes from the Hibbing paper 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 degrees or more off the microphone axis." Therefore, "At [XY recording] angles below 120 degrees the signal recorded from the rear are side inverted and above 120 degrees they are not."

Very cool! The paper does an amazing job of illustrating exactly how and why this occurs. So, it seems, if I had a pair of MKH50's setup in an XY configuration and attempted an equivalent 360 degree walk around test I would experience the exact same thing.

I do find it a bit strange that in all of my research of MS stereo mic'ing techniques almost nothing is mentioned about stereo-image side swapping when using a super-cardioid mid (maybe it's because most people are using the more popular cardioid pattern). In fact, before trying it myself, the only thing I read about using a super-cardioid pattern for recording in MS was that many people liked it for it's improved "focus" and off axis attenuation (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 thought I saw the purported value in this statement. But, it seems, the big mistake 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 mic in a stereo MS setup, when it actually does NOT. When the Mid and Side signals are decoded into stereo the end result is IDENTICAL to an equivalent XY setup (shown very clearly with diagrams in this paper: http://www.ribbonmics.com/pdf/technique.pdf) which means that the solo Mid super-cardioid mic'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 advantage of a super-cardioid's off axis rejection and are instead only giving yourself: 1) smaller recording angles, and 2) the potential for throwing rear lobe recorded signals into the opposite stereo speaker during playback. Therefore, I really do not see any advantage of using a super-cardioid mic over a cardioid for coincident stereo recording.

-Justin

[Yannick]

In the last paragraph there is a contradiction:

you are not giving up the advantage of a supercardioid mid mic, exactly because the recording angle is much smaller, so you need less side signal for the same stereo spread as with a omni mid.

Also, an MKH80/800 or 800 twin will sound very different when changing from omni to fig8 : the sound gets leaner, and you get less ambient info.

So, basically you change the recording angle without changing the side level, you are changing ambient pickup and you are changing the bass response of the array.

I recently did a solo piano recording in a big hall, with a MKH800 twin plus MKH30 MS setup, augmented by a MKH80 AB ambient pickup.
With the M=omni, the piano gets a bit loud/fat sometimes, with the M=supercardioid, the sound gets more focused and the bass actually sounds more natural, less exaggerated.

[aracu]

"Due to the fact that cardioid microphones record sound from all directions in phase the audio recorded from the rear is not side inverted."

This is misleading information, although it is true that in cardioid MS the audio recorded from the rear is not 100% inverted, but is approximately 50% inverted.

Try a 5 minute test with a 4 piece ensemble using a multipattern stereo mic (used a mid-side array), two players behind and two players in front of the mic. Shift through the polar patterns, starting with omni and ending with fig-8. With each change of polar pattern, the back two players become closer together then switch places to become completely inverted.

[Rolo 46]

Rear lobes can be jolly useful
But you have to be aware of the pitfalls implied
Most hyper cards are pretty ragged in their side and aren't first choice out of the Peli
An overview of stereo recording technique reveals flaws in all arrays,knowledge of these flaws is what makes a recordist experienced.

[apple-q]

Originally Posted by aracu

"
This is misleading information, although it is true that in cardioid MS the audio recorded from the rear is not 100% inverted, but is approximately 50% inverted.

What does 50% inverted mean? A door can't be open and closed at the same time.

[aracu]

Originally Posted by apple-q

What does 50% inverted mean? A door can't be open and closed at the same time.

I am trying to find words to describe listening to the stero playback of two musicians placed symetrically in back of a multipattern stereo mic set up as an ms array, and what happens while the mid mic, starting on omni setting, is switched progressively to wide cardioid (musicians sound closer together), then to cardioid (musicians sound like they are coming from approximately the same point), then to supercardioid (musicians sound like have moved apart, with musician which started out on the right now on the left, and musician which started out on the left now on the right), to fig-8 (musicians sound like they have moved further apart, musician which started out on the right now on the left, and musician which started out on the left now on the right).

[David Spearritt]

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."

As MS with a cardioid mid resolves to two coincident supercardioids the above statement is incorrect.

[Yannick]

Originally Posted by David Spearritt

As MS with a cardioid mid resolves to two coincident supercardioids the above statement is incorrect.

Lasttime I checked, with equal levels everything outside of the 104 (or was it 108) degree recording angle is ambiophonic, so is uncorrelated.
So it would seem the statement is correct after all. It depends on the superness of those supercardioids and the angle between them.
Eg. Consider two supercardioids at 180 degrees.

[Friscotch]

Originally Posted by aJustEnd

Is this an inherent problem with the MS recording technique, or could there be a problem with my figure 8 microphone?

-Justin

I once tested stereo coherence with Schoeps microphones in m/s configuration and here's what I noticed:
MK4 + MK8: front OK - rear OK
MK41 + MK8: front OK - rear reversed
CMIT + MK8: front OK - rear even more reversed than MK41

The hyper and super cardioid microphone in m/s configuration reversed the rear stereo signal. Not a big problem if one intends to use the sound in front of the mid mic, but definitely a problem if there is sound activity behind the mid mic.

In my tests, cardioid was the most suited mid microphone for a reliable stereo image in m/s recording.

Hope this helps...

[Rolo 46]

All MS is reliable
You just need to know your arrays and use them pragmatically.
A good rear is a useful resource (More Ms Johansson references,I apologise....)
Roger

[panatrope]

In all these discussions it is helpful to go back to basics.

Just remember that a cardioid is a combination of an omni and a fig 8 in equal proportions (equal parts pressure and pressure difference). Sounds from the front have the same polarity and add. At the side the fig -8 component has no influence so pressure only.

From the rear quadrants, the pressure diff component of the cardioid is the opposite polarity to pressure component (because the pressure difference - or 'velocity' - is in the opposite direction, cancelling the pressure component of the opposite polarity, and producing a null at the rear. However, because the pressure difference component is at all angles less than the pressure only, the resultant phase will be that of the omni component.

As the pattern is moved through hypercardioid to fig 8 (by changing the ratio of pressure to pressure difference in the pattern), part of the rear pattern will have the fig-8 component greater than the omni resulting in a discrete rear lobe, and sound picked up within the angle of this rear lobe will be of opposite phase to the omni, and the position reversal will become more obvious. It is most obvious in M-S Blumlein.

<And whom, may I ask, is this Ms Johansson? What am I missing ... >

[Yannick]

Originally Posted by Rolo 46

All MS is reliable
You just need to know your arrays and use them pragmatically.

+1
You could as well go around dissing AB omni setups because they do not image well on the sides, or the rear surround collapses in the front for musicians sitting closely behind the array...

A lot of MS dissing comes from the fact that it is a commonly misunderstood technique.
With the correct MS setups you can have good imaging 360 degrees around the mic, or very good surround imaging using a double MS (we can make it a contest: which mid pattern is best used for this?), up to completely reversing the rear image, which in some cases is exactly what you want.

On the other hand I never heard this comment about a Blumlein array.

And then you have to consider the vertical elevation angle as well... I almost never record at 1m height in a perfectly horizontal plane.

[Bibster]

Originally Posted by panatrope

<And whom, may I ask, is this Ms Johansson? What am I missing ... >

I'd love to show you some pictures, but the last bloke who did that got 10 years in jail for that, so...

[aracu]

Originally Posted by Rolo 46

All MS is reliable
You just need to know your arrays and use them pragmatically.

I agree with Rolo, the MS pattern is determined by the actual recording
situation and what best solves it's problems, which varies from one
recording to another.