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XY Technique - Neumann KM184

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XY Technique - Neumann KM184

Postby gandsound » Tue Sep 10, 2019 3:23 pm

It seems like there are some misconceptions about where exactly the diaphragm is on the Neumann KM184. I’ve seen some photos with the center of the XY right at the edge of the capsules and others with the center point somewhere in the middle of the capsules. Any thoughts?
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Re: XY Technique - Neumann KM184

Postby Hugh Robjohns » Tue Sep 10, 2019 8:19 pm

It's really not going to make any significant difference to the stereo imaging whether you align the front faces or the bottom of the capsule's rear slots, but the actual diaphragm is about 5 or 6mm behind the front face.

Personally, I rarely find crossed (XY) cardioids a useful stereo array, but if I do use it I usually set it up with the capsules overlapping by about 5cm to introduce a small amount of interchannel time difference which I think improves the imaging and sense of depth.

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Re: XY Technique - Neumann KM184

Postby ConcertinaChap » Wed Sep 11, 2019 11:00 am

Hugh Robjohns wrote:but if I do use it I usually set it up with the capsules overlapping by about 5cm to introduce a small amount of interchannel time difference which I think improves the imaging and sense of depth.

I've never heard of that technique (nothing new there, then :) ). I'll give it a try sometime.

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Re: XY Technique - Neumann KM184

Postby Arpangel » Wed Sep 11, 2019 11:13 am

Hugh Robjohns wrote:It's really not going to make any significant difference to the stereo imaging whether you align the front faces or the bottom of the capsule's rear slots, but the actual diaphragm is about 5 or 6mm behind the front face.

Personally, I rarely find crossed (XY) cardioids a useful stereo array, but if I do use it I usually set it up with the capsules overlapping by about 5cm to introduce a small amount of interchannel time difference which I think improves the imaging and sense of depth.

H

Hugh, can I just chime in here and ask if the OP's question applies to an M&S pair? I always set my cardioid mic about half an inch back from the front of the figure 8, as that's how I've always seen it done, with my MKH's anyway, any comments on this?
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Re: XY Technique - Neumann KM184

Postby Hugh Robjohns » Wed Sep 11, 2019 11:16 am

It apparently comes from the practical wisdom of Tony Faulkner, and was reported upon by the late, great Michael Gerzon in Studio Sound magazine in 1986 -- which is where I learned about it and have used it ever since:

https://www.americanradiohistory.com/Ar ... 986-07.pdf

(Page 122 onwards)
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Re: XY Technique - Neumann KM184

Postby Wonks » Wed Sep 11, 2019 11:26 am

(That's page 132 of the pdf document, but printed page 122).
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Re: XY Technique - Neumann KM184

Postby Arpangel » Wed Sep 11, 2019 11:37 am

Hugh Robjohns wrote:It apparently comes from the practical wisdom of Tony Faulkner, and was reported upon by the late, great Michael Gerzon in Studio Sound magazine in 1986 -- which is where I learned about it and have used it ever since:

https://www.americanradiohistory.com/Ar ... 986-07.pdf

(Page 122 onwards)

I think this subject could be another thread, but regarding an M&S pair, moving the mid capsule back further than fig 8 could be a bit confusing, as the side mic is picking up sound mainly from room reflections and not direct, like the mid mic, so they don't rely on sounds reaching them at the same time anyway, but could it, like your XY pair, in any way alter or improve the stereo image?
Thanks for that link, extremely interesting, I have others from that site as well, a great resource.
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Re: XY Technique - Neumann KM184

Postby Hugh Robjohns » Wed Sep 11, 2019 11:42 am

Arpangel wrote:Hugh, can I just chime in here and ask if the OP's question applies to an M&S pair?

He specifically mentions XY cardioids, so I don't think so, no!

I always set my cardioid mic about half an inch back from the front of the figure 8, as that's how I've always seen it done, with my MKH's anyway, any comments on this?

Obviously, this very much depends on the specific mics you're using, and the physical locations of the diaphragms in each mic.

With the Sennheiser MKH mics, the diaphragm in the MKH30 fig-8 is in sideways-on in the middle of the grille, so to align an MKH 40 or 50 (cardioid or hypercardioid) with that, the front of the grill would indeed be about 20-30mm back from the front of the MKH30, as shown below.

Image

... But this wouldn't be the case if you were using a ribbon fig-8, or even a dual-diaphragm multipattern LDC, or example...

Mid-Side is a coincident technique, so the diaphragms of the two mics should, theoretically, be aligned vertically, one directly above the other. However, that's not always practical so if there needs to be an offset to make mounting the mics easier, the stereo imaging is more stable if the diaphragm of the Side mic is fractionally behind the diaphragm of the Mid mic. So that the Side mic captures sounds fractions of a millisecond after the Mid mic.

If the Side mic is too far forward from the Mid mic, it captures sound first and so the leading transients in the stereo image start off 'out-of-phase' which creates the impression of an unstable image.

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Re: XY Technique - Neumann KM184

Postby Hugh Robjohns » Wed Sep 11, 2019 11:42 am

Wonks wrote:(That's page 132 of the pdf document, but printed page 122).

Thanks Wonks -- I was quoting from the paper mag I was reading in my library... :lol:
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Re: XY Technique - Neumann KM184

Postby Hugh Robjohns » Wed Sep 11, 2019 11:50 am

Arpangel wrote:...regarding an M&S pair, moving the mid capsule back further than fig 8 could be a bit confusing...

Absolutely! As I was saying...

...the side mic is picking up sound mainly from room reflections and not direct...

Not True! Any sound source which is anywhere off the centre-line will be picked up directly by both mics. This is an essential requirement to create the stereo imaging! The Side mic picks up a lot of room reflections as well, of course, but it's there primarily to capture direct sound from anything that's not directly front and centre!

...they don't rely on sounds reaching them at the same time anyway

Sorry... that's completely wrong. The stereo imaging results from the mathematical addition of the outputs from both mics, both of which capture the direct sound at exactly the same time, the amplitude (and polarity) of their contributions being entirely dependent on the angle of sound incidence and the polar patterns of the two mics.

Thanks for that link, extremely interesting, I have others from that site as well, a great resource.

There are so many fantastically interesting articles throughout the 1970s and early 1980s, especially from Gerzon about stereo, binaural, and ambisonics... Really well-written technical articles. It was a very fertile time in the audio/music production industry, and the education level was still relatively high... :shock:

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Re: XY Technique - Neumann KM184

Postby Arpangel » Wed Sep 11, 2019 12:17 pm

That's how I always set-up my M&S pair, with the mid mic about 20mm back. I do it because that's how I remember Mike Skeet doing it, but as you can see, there are huge gaps in my knowledge!
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Re: XY Technique - Neumann KM184

Postby Tomás Mulcahy » Wed Sep 11, 2019 6:44 pm

Hugh Robjohns wrote:https://www.americanradiohistory.com/Archive-Studio-Sound/80s/Studio-Sound-1986-07.pdf
Oh wow. What a resource. Thanks!

Great explanation of stereo shuffling. I finally get it. I'm off now to mangle everything in a DAW :D
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Re: XY Technique - Neumann KM184

Postby The Elf » Wed Sep 11, 2019 9:38 pm

And I'll be reading that interview with Peter Gabriel! ;)
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Re: XY Technique - Neumann KM184

Postby Mike Stranks » Thu Sep 12, 2019 9:50 am

... and a quick :clap: and :thumbup: to Mr Faulkner and all his works...

... second only to the esteemed Dr Robjohns in my estimation of people who know good stuff about how to record on location... :)
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Re: XY Technique - Neumann KM184

Postby Aural Reject » Thu Sep 12, 2019 9:52 am

I'll be digesting some of the serious stuff later....but the adverts.... :D :beamup:
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Re: XY Technique - Neumann KM184

Postby CS70 » Thu Sep 12, 2019 10:03 am

Hugh Robjohns wrote:It apparently comes from the practical wisdom of Tony Faulkner, and was reported upon by the late, great Michael Gerzon in Studio Sound magazine in 1986 -- which is where I learned about it and have used it ever since:

https://www.americanradiohistory.com/Ar ... 986-07.pdf

(Page 122 onwards)

Cool stuff. I'd never heard the word "shuffling" but when experimenting with stereo guitar recordings I've actively used Fabfilter Q in MS mode to shape the result - it does take L/R, converts to MS internally, allows you to EQ the two differently and then reconstructs the normal stereo signal.

Is it the same thing?

I vaguely remember useful results in reducing some string zings on the S channel without damaging the timbre. Didn't think at all manipulating the S would actually affect the stereo width :D
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Re: XY Technique - Neumann KM184

Postby Hugh Robjohns » Thu Sep 12, 2019 10:36 am

Tomás Mulcahy wrote:Great explanation of stereo shuffling. I finally get it.

You need to be a bit careful about 'shuffling' because the same word has several different and incompatible meanings and applications. All apply to stereo signal processing, but in very different applications. For example, EMI used the term in the 1950s and 60s in a completely different way and application to Blumlein in the 1930s!

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Re: XY Technique - Neumann KM184

Postby Hugh Robjohns » Thu Sep 12, 2019 10:40 am

CS70 wrote:I've actively used Fabfilter Q in MS mode to shape the result - it does take L/R, converts to MS internally, allows you to EQ the two differently and then reconstructs the normal stereo signal.

Is it the same thing?

Kind of, yes. Same basic technique, anyway. Shuffling in that context is about correcting anomalies in stereo mic arrays to improve imaging accuracy and so the filter parameter (amplitude and phase) are critical.

In your application you were just using a filter in the Side path to adjust the stereo width in a frequency-conscious way.

Didn't think at all manipulating the S would actually affect the stereo width :D

Of course it does -- that's the whole point! Reduce the Side signal to zero and you have mono. Make the Side signal as loud as the Mid signal and you have maximum stereo width. Go beyond that and you have outside-the-speaker spaciousness and mono-compatibility issues! :-D
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Re: XY Technique - Neumann KM184

Postby cyrano.mac » Sat Sep 14, 2019 10:10 am

This was known to me in the form of "stereo base control". I think I first saw it on a David Hafler designed Hifi preamp. It's never been really adopted in the home Hifi market.

I find it very useful on location, if I put up some small monitors. I can't always put these where I want, so if they're too close together, I'll widen the stereo image, if needed. If they're too far apart, I'll reduce it. Simple.

I hadn't heard about this variation on M/S though. Interesting. Thanks for the link, Hugh!

It is a bit counter intuitive. If I read that article right (I should reread it), they only correct below 600 Hz, roughly. I've always been told there's no directionality in very low frequencies. Like the signal from a subwoofer. Say, below 100 Hz. So how much directionality is there between 100 and 600 Hz.

TBH, I've never experimented with EQ combined with stereo base control, so I'm not positive either way.
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