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Author Topic: XY Greater than 90 Degrees?  (Read 2276 times)

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Offline EmRR

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Re: XY Greater than 90 Degrees?
« Reply #15 on: January 19, 2020, 12:19:17 AM »
Thank you all for very nice posts. I have been thinking a long time about xy and mid/side. When we are changing mid/side ratio in post of stereo track of mics in xy, are we changing a resulting angle and directionality of mics? Can we use for example cardiods in xy at narrow angle and then change it in post to virtual hyper cardiods at wider angle?

Another great paper to find and look through is Wes Dooley's AES paper about mid-side.  It has pages and pages of equivalent mic patterns.

Control involving both mic pattern and angle is more the territory of ambisonics, and you can get most of that with a native B format array using two figure 8's and an omni, then encode with one of the many ambisonics plugins.  You just won't get the height element of full ambisonics.   You can also create multiple virtual patterns for surround, or if you need a center mic along with a widely angled hyper pair, etc. 
« Last Edit: January 19, 2020, 12:24:58 AM by EmRR »
Mics: DPA 4060 w/MPS 6030 PSU/DAD6001/DAD4099, Neumann KM 131, KMR 81i, Oktava MK 012, Sennheiser MKH 105, MKH 20, MKH 30, MKH 40, MKH 800 TWIN, lots of other studio appropriate choices
Recorders: Zoom F8n, Sony MZ-R50, portable MOTU based multitrack DAW for client work

Offline kuba e

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Re: XY Greater than 90 Degrees?
« Reply #16 on: January 19, 2020, 01:59:48 AM »
Thanks EmRR. It is helpful document. I found it on google, here it is:
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&ved=2ahUKEwiyw7i1gY_nAhWLEVAKHfT8AigQFjAEegQICBAB&url=https%3A%2F%2Fwww.gearslutz.com%2Fboard%2Fattachments%2Fall-things-technical%2F156765d1265402712-excellent-x-y-stereo-sdc-cardioid-mic-field-use-schoeps-x-y-clone-technique.pdf&usg=AOvVaw0gH9AYQVXAHF2ZnM4y5ipu

It is difficult to imagine it. I just guess the following. We can decompose the directional pattern on an omni and a fig8. So, if we mute mid in xy track, the result are two crossed fig8. And we can decode two crossed fig8 in mid/side as one forward facing fig8 and one side facing fig8 (Fig 2a in the Wes's document). So is the final result side facing fig8? And if we mute side in xy track we get some directional pattern facing forward?

Offline DSatz

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Re: XY Greater than 90 Degrees?
« Reply #17 on: January 19, 2020, 02:27:38 AM »
I promise this will get to an interesting and useful place after a moment.

Do "kids today" know how stereo FM radio works? FM broadcasting was introduced as a mono-only medium, and then stereo was "grafted on" as a retrofit. The way this was done is very similar in principle to M/S. To simplify somewhat: At the radio station, the left and right program channels are fed into a matrix. One output of the matrix is L+R (the "sum"), while the other output is L-R (the "difference"). The "sum" signal would modulate the station's carrier frequency directly if it was a mono station--as they all were originally, and then there were several transitional years during which only some FM stations were stereo, while all others remained mono and only gradually converted.

If the station was broadcasting in stereo, the "difference" information would modulate a second, somewhat higher-frequency carrier, and the result would then become part of the signal that modulated the main carrier--all happening in real time, analog processing, so that it was really synchronized and simultaneous. Finally, a 19 kHz "stereo pilot" tone was added in at a low-ish but constant level (and possibly a secondary program channel which could be entirely unrelated if present; I'll leave that mess out, though).

A mono receiver simply demodulates the received signal, chops off everything above 15 kHz, and plays that back as mono; no problem.

A stereo receiver demodulates the signal, chops off everything above 15 kHz (which produces L+R a/k/a mono as above), but also checks for a 19 kHz stereo pilot signal. If it's present, the receiver knows to lock onto the secondary carrier (38 kHz above the baseband as I recall) and demodulate that as well, producing L-R a/k/a the difference channel. It then matrixes the two received signals together; (L+R) + (L-R) = 2L, while (L+R) - (L-R) = 2R; and voila, you have the original stereo signal back again.

As this illustrates, ANY two-channel signal--in fact anything that you can stuff into two channels, whether it's the left and right halves of the same program, or two completely unrelated signals (!)--can be matrixed into L+R (sum) and L-R (difference), then transmitted and/or recorded, and finally dematrixed back to the original signals (e.g. L and R) again on the receiving end. So this is certainly true for X/Y microphone signals. But in principle it doesn't even need to be two coincident microphones, or even microphones that are (or were) at the same concert at the same time!

However, if you do use this trick (matrixing / dematrixing) with a coincident (X/Y) pair of microphones that are at the same concert at the same time, then the nice thing about the L+R sum is that it is (if you've set up appropriately and the acoustics gods are with you) a listenable mono signal in case there's a use for that. Conversely, back in the 1950s when recording engineers were first learning to record stereo for FM broadcast and classical record production, they were all experienced as mono engineers (since that's all there was for many years), and M/S allowed them to continue using those skills while producing mono-compatible stereo recordings. This method was used very widely in Europe, while spaced-microphone stereo became the norm in the U.S. due to the influence of Bell Labs.

Back to our world today: Any X/Y recording may be translated (matrixed) to M/S "signal format" and vice versa without limit. You can derive the sum and difference from any X/Y recording, then (if you like) process the M or S channel separately, then recombine them to L/R stereo. I typically like to boost the low frequencies in the "S" channel to improve spaciousness; it doesn't really matter whether I'm starting from an X/Y or an M/S recording, although starting from M/S saves me a processing step.

--Dr. Noah said: > Speaking of mid/side, perhaps it's greatest advantage over x/y is that the angle can be changed in post.

X/Y and M/S are equivalent in principle--just different "encodings" of the same information. There's really nothing that you can do in one that you can't do in the other.

The technique that you're referring to involves changing the overall proportion of M signal to S signal. And when you do that, you not only change the stereo image width, you also change the amount of reverberation in the stereo recording. If you increase "S" in post, it's as if you've time-traveled back and spread your original X/Y microphones farther apart--but at the same time, altered their pickup pattern toward a greater degree of reverberation and a lower proportion of direct sound. You can't have one without the other in conventional M/S <-> X/Y.

In my experience this has been a real limitation; only one narrow range of M-to-S gain ratio settings yields a plausible degree of reverberation for the image width that you get with it. So you can sometimes use this approach to improve an X/Y recording up to a point--but it won't give you independent control over these two important parameters of the recording separately from one another. If you want fully independent control over the stereo image width AND the amount of reverberance in the recording, you need at least three microphones--either "double M/S" as Schoeps calls it (a regular M/S pair plus a separate, rear-facing capsule with its own recording and processing channel) or so-called "horizontal Ambisonics". (Or real Ambisonics, of course.)

--best regards
« Last Edit: January 19, 2020, 09:27:02 AM by DSatz »
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Offline kuba e

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Re: XY Greater than 90 Degrees?
« Reply #18 on: January 19, 2020, 04:50:04 AM »
Thank you very much David. It is nice from you that you take your time to explain mid-side manipulation. It is very helpful.

I was thinking about a non-standard thing that sounds strange. I have only cardiod and omni mics. If I need to record in xy with more directional microphones, I could use cardiods. I could set narrow angle and then lower mid/side ratio. Probably not a win with cheap microphones. But maybe it would work a little bit. Maybe it would be a small help for hobby taper.
« Last Edit: January 19, 2020, 04:53:41 AM by kuba e »

Offline DSatz

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Re: XY Greater than 90 Degrees?
« Reply #19 on: January 19, 2020, 09:51:23 AM »
kuba, yes, you could record with coincident cardioids, then afterward matrix to M/S, boost S, then rematrix back to L/R stereo. This could make the recording more interesting and fun to listen to, particularly if your cardioids are single-diaphragm and (preferably) small or small-ish.

(If they're dual-diaphragm, unfortunately you won't have much low-frequency energy in the S channel. That's because the cardioid patterns of dual-diaphragm microphones "widen out" at low frequencies, particularly in microphones that use a shared-single-backplate capsule design; the result is an S channel with attenuated bass, since both microphones are picking up mostly the same stuff at the same time, and the matrix simply cancels it all out.) (Again, forgive me for being repetitious, but this is why I maintain that large-diaphragm, dual-diaphragm cardioids are a poor choice for coincident or closely-spaced setups.)

But there's a limit to how much you can stretch things with this technique and still have it sound natural. Try listening to that S channel signal by itself some time--it's not entirely wonderful sounding, since it contains a large helping of far-off-axis pickup, which in many cardioids can be somewhat "bright and boomy". Boosting it a few dB can be a big help; boosting it many dB, not so much. Past a certain point the stereo playback can start to sound "phasey". Injecting large amounts of the same signal into both channels in opposite polarity isn't a lot better than injecting it into both channels in like (equal) polarity; you never want that component of your signals to become obvious, let alone dominant, in the playback.

All in all it's still best if you can put optimal microphones in the optimal position(s) before pressing the "record" button.

--best regards
« Last Edit: January 19, 2020, 04:21:41 PM by DSatz »
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Offline EmRR

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Re: XY Greater than 90 Degrees?
« Reply #20 on: January 19, 2020, 12:11:47 PM »
--Dr. Noah said: > Speaking of mid/side, perhaps it's greatest advantage over x/y is that the angle can be changed in post.

X/Y and M/S are equivalent in principle--just different "encodings" of the same information. There's really nothing that you can do in one that you can't do in the other.

In theory, yes.  In practice I find a lot of cases with XY or Blumlein comparing stereo versus collapsed mono (or even a narrowed image) reveals an unhappy loss of high frequency information.  If I'm combining multiple recording passes in the studio and don't know what the client is going to want (insist?) regarding stereo spread, MS is the more reliable path to a sound I'll be happy with anywhere from mono to hard panned stereo.   Same goes for post-processing of 2 track live recordings.    That's my only caveat.  If you're not ever changing width, you don't need MS. 

Back on topic, XY at concerts where XY orientation may be pretty much a PAS situation, XY may win. 

Then as you mentioned, DMS or horizontal Ambisonics (native B format as I called it) give many more options after the fact....cue the dual output mic once more...    Again, ruler flat mics with great pattern control really help both techniques. 
Mics: DPA 4060 w/MPS 6030 PSU/DAD6001/DAD4099, Neumann KM 131, KMR 81i, Oktava MK 012, Sennheiser MKH 105, MKH 20, MKH 30, MKH 40, MKH 800 TWIN, lots of other studio appropriate choices
Recorders: Zoom F8n, Sony MZ-R50, portable MOTU based multitrack DAW for client work

Offline kuba e

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Re: XY Greater than 90 Degrees?
« Reply #21 on: January 19, 2020, 02:20:13 PM »
Yes you mean manipulating left/right components vs. manipulating mid/side components. And David means encoding left/right vs. encoding mid/side.

This is for someone who is like me. This discussion was good for me to realize that a pair of directional mics (cards, hypers, blumlein) in XY has always twin in a M/S pair (directional mic + fig8). XY pair has parameters - polar pattern and angle. M/S pair has parameters - polar pattern of mid and mid/side ratio. And there is always possibility to recalculate XY parameters to M/S parameters and replace XY pair with M/S pair and vice versa.  The relationship between XY parameters and M/S parameters is interesting. All can be derived from the fact that each directional pattern can be decomposed into omni and fig 8. So for example it si possible to show when we lower mid/sid ratio of XY pair that it is equal as another XY pair with wider angle and more directional polar pattern.  Of course all this is valid only for theoretical profiles, practice profiles differs. I hope I didn't write it confused or wrong.

Please, do you know whether there is Ambisonic plugin that is able to show how is changing XY pair when we are changing it's mid/sid ratio?

Back on topic, XY at concerts where XY orientation may be pretty much a PAS situation, XY may win. 

Please, XY may win compared to what configuration?


Offline EmRR

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Re: XY Greater than 90 Degrees?
« Reply #22 on: January 19, 2020, 02:53:52 PM »
Please, do you know whether there is Ambisonic plugin that is able to show how is changing XY pair when we are changing it's mid/sid ratio?

Ambisonics plugs show intended pattern and angle, but won't do anything with a 2 channel MS signal.  I don't know of any MS plugs that show pattern and angle, but there may be one. 

Back on topic, XY at concerts where XY orientation may be pretty much a PAS situation, XY may win. 
Please, XY may win compared to what configuration?

Mid Side, which, depending on the mic, may not have optimal response at the angles of the PA compared to the mics.
Mics: DPA 4060 w/MPS 6030 PSU/DAD6001/DAD4099, Neumann KM 131, KMR 81i, Oktava MK 012, Sennheiser MKH 105, MKH 20, MKH 30, MKH 40, MKH 800 TWIN, lots of other studio appropriate choices
Recorders: Zoom F8n, Sony MZ-R50, portable MOTU based multitrack DAW for client work

Offline kuba e

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Re: XY Greater than 90 Degrees?
« Reply #23 on: January 19, 2020, 03:34:23 PM »
I think it is equal. If we choose right mid/side ratio of M/S pair we get optimal response at the angles of the PA. We can also control the response outside this two angles. This can be controlled by choosing the right mid/side ratio together with the right polar pattern for mid microphone. It is the same as choosing the right angle and the right polar pattern for a XY pair. It is just entered in a different encoding.

Offline EmRR

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Re: XY Greater than 90 Degrees?
« Reply #24 on: January 19, 2020, 06:36:10 PM »
I think it is equal.

Not if the treble pattern of the mic is very beamy in nature, it isn't.  You won't get equal results from LDC's. 

'Perfect' mics, yeah, it's equal or close to it. 
Mics: DPA 4060 w/MPS 6030 PSU/DAD6001/DAD4099, Neumann KM 131, KMR 81i, Oktava MK 012, Sennheiser MKH 105, MKH 20, MKH 30, MKH 40, MKH 800 TWIN, lots of other studio appropriate choices
Recorders: Zoom F8n, Sony MZ-R50, portable MOTU based multitrack DAW for client work

Offline DSatz

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Re: XY Greater than 90 Degrees?
« Reply #25 on: January 19, 2020, 08:16:05 PM »
EmRR, thank you and yes: One can always translate between X/Y and M/S signals in either direction--but each particular, actual X/Y or M/S setup still has its own particular characteristics. It is a little like the famous line at the start of Tolstoy's Anna Karenina: "Happy families are all alike; each unhappy family is unhappy in its own way."

As an example to clarify this, think of an M/S pair with a shotgun microphone as its M microphone. Shotguns, as we know (or should know) have directional patterns that become increasingly irregular at upper-mid and high frequencies; taken on a broad average, they get narrower than the low- and low-mid-frequency pickup pattern--but at any one frequency above that, they have "lobes" at various odd angles--a rather wild pattern which is ultimately the reason why professionals avoid using them indoors whenever possible. If you make an M/S recording like that and matrix it to X/Y, the equivalent "microphones" of your virtual X/Y pair will have directional characteristics unlike those of any real-world microphone, and of course quite different depending on which frequency above the midrange you consider.

(I am assuming, perhaps incorrectly, that people here are conscious of the ways in which the directional patterns of most microphones vary across the frequency range--with large and/or dual-diaphragm and/or interference-based microphones being the worst offenders, and cardioid being the midpoint on the spectrum that often shares the defects of both extremes rather than escaping them. "He who stands in the middle of the road gets hit by trucks going both ways.")

So I'm not saying that for each X/Y or M/S pair that we could set up with microphones that you or I happen to own, there's an exactly equivalent setup of the other kind that we could also make with microphones that we happen to own (or which even exist at all). There are still reasons to choose particular microphones and particular setups in particular situations!

But matrixing can give you the sum and difference of any two inputs--and if those inputs are a symmetrically arranged coincident pair (X/Y), the outputs will be functionally a mid-side pair of signals (M/S) and vice versa, and you can flip back and forth between the two realms and perform the kinds of processing that belong to each realm.

--best regards
« Last Edit: January 20, 2020, 01:02:38 PM by DSatz »
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Offline kuba e

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Re: XY Greater than 90 Degrees?
« Reply #26 on: January 20, 2020, 08:11:01 AM »
Thank you all, it is starting to be more clear for me. EmRR, I read the documents you recommended. There is one example of advantage/disadvantage of XY/MS - XY with large angle. The disadvantage of XY with large angle is "the microphones are then mostly addressed from the side which causes the directional properties to be very frequency dependent." And second addition "The directional characteristics of the S microphone are almost ideal since its figure-of-eight polar pattern is almost frequency independent. For that reason the S microphone can record objectively even from the side". I understand this.

Just because of my curiosity - when we reduce the microphone types only to good quality small diaphragm and target only to stereo playback - are there more general practical rules when to choose XY or MS or is there only little difference (except the first case)? In general, in the terms of bass response, is there any advantage / disadvantage?
« Last Edit: January 20, 2020, 08:39:38 AM by kuba e »

Offline EmRR

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Re: XY Greater than 90 Degrees?
« Reply #27 on: January 20, 2020, 12:21:04 PM »
Generally speaking with SDC's and distance, the closer to omni you are the more bass you have, with less as you pass from cardioid through hypercardioid on to figure 8.    Mics like the MKH30 are the rare 8's with reasonably flat bass, but in comparison to other MKH series mics they are still the thinnest sounding.....until you get up close (within a meter or so) and then they have the greatest proximity effect, and can give more bass than an omni.   So as always, there are interconnected variables. 
Mics: DPA 4060 w/MPS 6030 PSU/DAD6001/DAD4099, Neumann KM 131, KMR 81i, Oktava MK 012, Sennheiser MKH 105, MKH 20, MKH 30, MKH 40, MKH 800 TWIN, lots of other studio appropriate choices
Recorders: Zoom F8n, Sony MZ-R50, portable MOTU based multitrack DAW for client work

Online Gutbucket

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Re: XY Greater than 90 Degrees?
« Reply #28 on: January 20, 2020, 12:49:14 PM »
Bringing it on home in the taper world-

Go full on Russian literature and leverage family unhappinesses to personal advantage.. the lovely princess Stereophonie working her influence and charms to singular effect. 

Consider this approach:
Given a relatively distant recording location (aka typical "taper" in a bar positions), start with P.A.S. - that is to say, angle the microphones so that they are pointed directly at the PA stacks, placing those primary sound sources directly on-axis, which also serves to keep on-stage sound sources relatively close to on-axis as well in the shared overlap region.  Then adjust the other variables around that practicality-driven starting-point.   What other variables?  Choice of pickup pattern, choice of spacing between microphones (including no spacing at all for coincident X/Y), and choice of mid/side ratio re-adjustment.  These variables all interact with one another. One is forced to decide on the first two prior to making a recording, but the last needn't be decided upon until after the recording has been made.

Once back at the bat cave, convert Left/Right X/Y to Mid/Side and adjust the Mid/Side ratio while listening to dial in the desirable stereo width.  That Mid/Side representation is converted back to Left/Right prior to listening.  In pointing directly at the PA speakers, the physical microphones have been aimed with the real-world behavior of imperfect polar patterns, taper recording locations in real-world rooms.  One then effectively (re)points virtual microphone patterns to achieve the prefered stereo spread.  This is the pursuit of a best of both worlds approach.

^Taking it a step further, one can EQ Side differently than Mid , affecting stereo width by frequency range, such as boosting low frequency Side content to increase low frequency spaciousness without mid and high frequency content being portrayed as overly wide.

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Online Gutbucket

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Re: XY Greater than 90 Degrees?
« Reply #29 on: January 20, 2020, 12:59:25 PM »
As mentioned by others above, when choosing an appropriate mid/side ratio for a straight stereo pair, the range in which an optimal adjustment can be found is relatively small, and when such a mid/side ratio-readjustment is performed on stereo material recorded using non-coincident spaced microphone techniques, the range is typically smaller yet.

Regardless of the nature of the stereo signal, this poses no problem for properly received and decoded stereo FM radio because the encoding and decoding ratio is identical on both ends of the transmission.  There is is no change of overall Mid/Side ratio when the transmission is received correctly.  However, if there is a problem with FM transmission such that the stereo sideband carrier cannot be properly received and only the primary mono band is heard (the monophonic sum of Left and Right, equivalent to a change of Mid/Side ratio to 100:0), there might be issues with comb-filtering in the mono sum of content recorded using non-coincident microphone techniques.

It's not so much Mid/Side verses X/Y (both representing coincident configurations) but coincidence versus non-coincidence of a microphone pair which is a more important differentiator considering how much of a mid/side ratio readjustment one might be able to make without introducing unwanted problems.
« Last Edit: January 20, 2020, 03:33:03 PM by Gutbucket »
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