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Gear / Technical Help => Microphones & Setup => Topic started by: Chuck on August 31, 2018, 02:33:51 PM

Title: M/S audience with SBD feed matrix
Post by: Chuck on August 31, 2018, 02:33:51 PM
I just had a crazy idea. I'm sure someone has done this...

Set-up a figure 8 and a source facing cardioid in the audience (aligned on top of each other) to capture the audience and PA mid/side. Then mix that with a soundboard feed. Of course you have to time align the AUD and SBD sources in post.

I've been recording in local venues more recently and am get bored of mixing a DIN cardioid pair in the audience with the sound board feed. I do have a an LD figure 8 mic that I've used a few times to mess around with M/S. I don't usually like the results of M/S recording unless I'm really close to the source. But, using a mid side pair in the audience to mix with the SBD feed would be cool. I could control the width of the audience/PA in post.

Another potential benefit... M/S is mono friendly and could really add controllable width to mono SBD feeds.

If anyone has done this, let me know how it sounded. This could breath new life into my stagnant way of doing SBD/AUD matrixes.
Title: Re: M/S audience with SBD feed matrix
Post by: Chuck on August 31, 2018, 02:36:43 PM
Wow, I posted too quickly...

What if I used the mono SBD feed as a replacement for the mid mic when decoding?? No need for the mid mic!


Title: Re: M/S audience with SBD feed matrix
Post by: rippleish20 on August 31, 2018, 04:18:58 PM
 The FOH for the band I record most loves M/S  and I've been playing with M/S recently (he encouraged me).  I have done both of what you described - a SBD matrix and a SBD matrix with just the side.but my problem is that, as you, say, you really need to be in the perfect position to make it worthwhile and thats hard to do. Dan Healy actually settled on using M/S audience recordings for the matrixes he did, which he called the Ultra-matrix. He apparently found it to generally be preferable over microphones on stage etc...

Quite honestly, I am moving more towards on stage microphones myself, although you can do M/S there too. There is so much talking at shows these days, I am disillusioned about recoding from the audience at most shows period (except outdoors)...
Title: Re: M/S audience with SBD feed matrix
Post by: Chuck on August 31, 2018, 04:47:43 PM
Thanks for the info rippleish20. Of course I've heard those Healy recordings. But, I didn't know the audience source was M/S. I'm going to try it out next time I get the chance.

edit to add:

My side mic will be a two diaphragm switchable pattern LD.
Title: Re: M/S audience with SBD feed matrix
Post by: chk on August 31, 2018, 05:08:53 PM
Believe Healy or the ultrasound guys ran an AKG C42 most of the time for the aud feed of ultramatrix recordings with the mid channel pattern set to omni.
Title: Re: M/S audience with SBD feed matrix
Post by: rippleish20 on August 31, 2018, 06:00:16 PM

I ran across a Healy interview at one point where he described his Ultra-matrix but I can't readily find it at the moment. He described how he tried microphones on stage but the results varied too much -  from really good to terrible sounding - so he settled on M-S using a microphone at the soundboard.


http://forums.stevehoffman.tv/threads/the-grateful-dead-live-sound-and-recording-legacy-thread.500719/page-4

Someone is this thread suggested AKGs but "were first a pair of AKG 414EB then AKG c424b or AKG c422b"
Title: Re: M/S audience with SBD feed matrix
Post by: EmRR on August 31, 2018, 06:09:00 PM
Wow, I posted too quickly...

What if I used the mono SBD feed as a replacement for the mid mic when decoding?? No need for the mid mic!

I wonder what that does sound like.  At first blush it seems a no-go for a lot of reasons, but maybe there's some effect.  Thing is it won't give any stereo impression of the audience if there's no center for the audience to encode from.  It may make more of a pseudo-stereo effect on the band and cancel a lot of the audience.  I'll have to try it.....
Title: Re: M/S audience with SBD feed matrix
Post by: Gutbucket on August 31, 2018, 06:20:18 PM
[Edited to reply the the above while I was typing the message below..  ^ Yep, sort of. The stuff picked up by the single 8 AUD portrayed in a pseudo stereo "wider and enveloping" sense rather than a discrete left/right imaging sense. It won't cancel out the audience though unless you sum the resulting stereo output to mono.]


A Mid/Side pair works fine as an AUD source mixed with the SBD.  Think of it as similar to running an X/Y supercard AUD.  It will definitely work, just as any other coincident AUD setup will.  If you prefer it or not is a different question.

Technically, you cannot substitute the SBD feed for the Mid signal in combination with an AUD positioned Side fig-8 and expect virtual X/Y-like stereo patterns from that.  The Mid and Side "sampling points" need to be fully coincident both with respect to time-of-arrival and position-in-space for that.  But we aren't taping to please theoreticians nor derive textbook virtual pickup patterns.  Yet in practice it can work fine, as long as it sounds good..  And In actuality, that is partly what you are doing by Mixing the SBD in with the AUD anyway.  Consider that by matrixing the (primarily monophonic) SBD with the AUD you are effectively modifying the Mid component of the summed Left/Right stereo output more than its Side component.  How much depends on the mix ratio of SBD to AUD.  The difference is a matter of degree, and how you think about it.

Really, Mid/Side decoding is little more than mixing, with the twist of using only one channel for Side, and inverting polarity of that to one speaker versus the other.  When mixing for 2 channel stereo, I sometimes use my single rear-facing ambience microphone as Side channel, "mixed" in via Mid/Side with my single forward facing directional center microphone.  I typically do that to help spread the auditory center a bit so that it blends more smoothly into the stereo panorama with my other Left/Right mic channels instead of seeming to stand apart as a focused center-forward point-source.  Thought of another way, it helps spread out the rear-facing microphone information out so as make the ambient contribution from it more wide and diffuse in the playback image, rather than being reproduced as a narrow monophonic central point-source of ambience competing with what the forward-facing center microphone is providing.

You can use any microphone pattern as the Side channel- an omni, a cardioid or whatever.  When approaching Mid/Side in this way, "mixing to add width, diffuseness and depth" rather than as a way of achieving clear and predictable Left/Right locational imaging, it becomes advantageous to limit as much as possible how much Mid information gets into the Side channel.   A sideways-facing figure-8 does that somewhat, yet still picks up a lot of information from the front as well to either side of the central null.  Here is one of the basic things I've come to realize- Side channel used this way, and Ambience channels in general, become far more useful when they exclude the direct sound from the stage and PA to the greatest degree possible, as long as you already have sufficient direct sound. But that's somewhat different than AUD + SBD when both are focused on picking up the band on stage to the exclusion of all else.  If the SBD is not a complete mix, you'll need the AUD to provide what isn't in the SBD.  If the SBD is a complete and good sounding (if dry) mix, all you really want from the AUD is good diffuse ambience and audience reaction.  An omni Mid worked well for ambience in Healy's Ultramix because it was placed back at the SBD, far enough from the PA that it was primarily in the diffuse field.  Mid/Side with an omni Mid decodes to sideways-facing opposing cardioids patterns, remaining omnidirectional in an overall combined sense.

There was a similar technique to Healy's from the late 80's / early 90's which I've heard about, which was used by some folks recording material for matrixed Dolby surround.  Analog matrixed Dolby surround was a 4 channel format- LRCS = Left,Center,Right,Surround.. with the surround channel being monophonic (essentially Side channel in the sense I describe using it above).  This technique for recording the S channel was to place a pair of sideways-facing coincident cardioids well back in the room, and to flip polarity of one of them before summing them and feeding that into the S input of the matrix encoder.  If you think about that, it is essentially the same as using a single sideways-facing figure-8.

All good, but..
Title: Re: M/S audience with SBD feed matrix
Post by: Gutbucket on August 31, 2018, 06:34:17 PM
I prefer going the opposite direction-

Using wider-spaced and/or more widely angled AUD mic arrangements when good SBD (or other good direct-sound content) is available, rather than more-narrowly spaced or coincident AUD mic arrangements.  That's because I'm getting more than enough well-balanced, strongly-MID-dominated direct-sound content reinforcement from the SBD, and what I want mostly from the AUD pair is more open, diffuse, decorrelated ambience to provide depth, make things sound more live, less canned, and more real.

An omni Mid in the AUD Mid/Side pair rather than a forward directional pattern helps do that.  But so does spacing the AUD mics further apart, which also randomizes the phase of the ambience more and decorellates it nicely so the ambience and audience sounds deep, diffuse and all-encompassing rather than flat and narrow.

The thing to think about in balancing all this via how you setup is how much direct PA and stage sound you want in your AUD when you also have SBD available.  If the SBD sucks or is incomplete, you'll need to rely on the AUD mics to pull the direct PA and band sound and use the SBD more as salt to taste.

If the SBD is complete, you can get a better matrix by limiting how much of the stuff that is already in the SBD gets into your AUD mics.  A wide pair of omnis as AUD works great as it still gets plenty of PA and stage sound, but in a more distant sounding way.  It complements the SBD rather than competing. If the SBD has some stereo stuff, that will images across the center while the audience and ambience stays wide, diffuse and "out of the way" of the stuff of primary interest in the center.  But wider spaced cards, or even wider angled cards at your prefered standard spacing will do some of that too.  This is more of a "searching for the right balance", "middle-way" approach, rather than an all or nothing kind of thing.  Too much clearly discernible audience in that AUD pair?  Point them away from the nearby audience. 

On stage with your primary coincident or near-spaced pair at center stage?  Consider that like a SBD feed and place your on-stage AUD pair wide, maybe facing the band obliquely from the sides, maybe facing the ceiling- basically aiming to get more ambience and early reflections than audience in that pair if the audience is less than desirable or simply too loud. 

Arrange things so that both sources do what they do best without fighting each other.
Title: Re: M/S audience with SBD feed matrix
Post by: Gutbucket on August 31, 2018, 07:01:04 PM
Just a note for you guys already reading.. I did some heavy revision to the posts above, especially the second.
Title: Re: M/S audience with SBD feed matrix
Post by: DSatz on August 31, 2018, 08:09:09 PM
Chuck wrote:

> I don't usually like the results of M/S recording unless I'm really close to the source.

I'm not sure how close "really close" is for you, but in general this opinion makes a fair amount of sense to me. The idea of M/S is for the "M" microphone to pick up mainly direct sound--with some ambience, of course, but no more than would be desirable in a mono recording or broadcast. When you choose your "M" microphone and its placement, you basically have to think like an engineer from the 1950s or before.

All you young whippersnappers (get off my lawn!) who grew up in the years since stereo became ubiquitous--you have it easy. You can accept far larger amounts of reflected (room) sound relative to direct sound in your recordings than engineers could in the mono era. Stereo lets the listener's ears and brain sort things out somehow, even in some cases when there's more reflected sound than direct sound.

Put another way, in reverberant spaces, acceptable stereo recordings can be made at greater miking distances than good mono recordings can be. Your brain can't localize anything in a mono recording, so it doesn't take very much ambience to make a mono recording sound muddy; the direct/reflected sound balance is more critical. You also have to pay more attention to the character of the reverberation that you do pick up. Whatever room sound you record in mono had better complement the direct sound or else it can detract, perhaps severely so.

Again, listening for those things is part of the skill set that engineers had to have in the pre-stereo era. Stereo lets you get away with not listening as closely; there's more room for a mediocre sound balance when localization is there for the listener's brain to fall back on.

But when you record in M/S, you really have one foot in the mono era, or maybe even both feet. The "S" microphone has to be placed with the "M" microphone and pick up its own mix of direct and ambient sound. But again that mixture is critical, and it MUST include a substantial helping of direct sound--otherwise the matrixing function (M + S = L, M - S = R) can't possibly produce consistent directional cues for the direct sound. If your mikes are so far back in the room that the "S" mike is overwhelmed with reverberant sound, then the M/S technique is just churning out fake stereo from ambience information.

By the way, since all X/Y methods (including Blumlein!) are equivalent restatements of M/S and vice versa, the same criteria hold true for them.

--best regards
Title: Re: M/S audience with SBD feed matrix
Post by: kuba e on September 01, 2018, 07:16:40 AM
Thanks you all for very interesting posts.

Put another way, in reverberant spaces, acceptable stereo recordings can be made at greater miking distances than good mono recordings can be. Your brain can't localize anything in a mono recording, so it doesn't take very much ambience to make a mono recording sound muddy; the direct/reflected sound balance is more critical. You also have to pay more attention to the character of the reverberation that you do pick up. Whatever room sound you record in mono had better complement the direct sound or else it can detract, perhaps severely so.

Please, could someone say little about the reverberation character? I wonder, I would find more about it, but unfortunately I do not know what to look for. I do not know the terminology.

Again, listening for those things is part of the skill set that engineers had to have in the pre-stereo era. Stereo lets you get away with not listening as closely; there's more room for a mediocre sound balance when localization is there for the listener's brain to fall back on.

But when you record in M/S, you really have one foot in the mono era, or maybe even both feet. The "S" microphone has to be placed with the "M" microphone and pick up its own mix of direct and ambient sound. But again that mixture is critical, and it MUST include a substantial helping of direct sound--otherwise the matrixing function (M + S = L, M - S = R) can't possibly produce consistent directional cues for the direct sound. If your mikes are so far back in the room that the "S" mike is overwhelmed with reverberant sound, then the M/S technique is just churning out fake stereo from ambience information.

By the way, since all X/Y methods (including Blumlein!) are equivalent restatements of M/S and vice versa, the same criteria hold true for them.

I often record from the back of the room either because of club policy or unwillingness to be in the big crowd. I use the Gutbucket PAS microphones configuration to increase the ratio of direct sound to ambient. I've always liked recordings with a larger microphones spacing. It's nice to see this problem from the perspective of stereo vs. mono and Mid/Side.

Title: Re: M/S audience with SBD feed matrix
Post by: kuba e on September 01, 2018, 07:50:36 AM
All you young whippersnappers (get off my lawn!) who grew up in the years since stereo became ubiquitous--you have it easy but you may not realize it. You can accept far larger amounts of reflected (room) sound relative to direct sound in your recordings than engineers could in the mono era.

In the next fifty years engineers from the 1950s will be heroes. Even they are already now. And Deadhead tapers will be masters. It's a huge jump. Hobby taper, who is recording for joy, has incredible possibilities today.
Title: Re: M/S audience with SBD feed matrix
Post by: Chuck on September 01, 2018, 09:53:32 AM
Chuck wrote:

> I don't usually like the results of M/S recording unless I'm really close to the source.

I'm not sure how close "really close" is for you, but in general this opinion makes a fair amount of sense to me.

Often in small clubs/bars the ideal spot to set-up M/S is where people are standing, dancing etc... Places it's just not practical or allowed by the venue to put up a mic stand.
Title: Re: M/S audience with SBD feed matrix
Post by: DSatz on September 03, 2018, 07:36:06 PM
> could someone say little about the reverberation character?

kuba e, even if you don't know the terminology, I think this is mostly a matter of common sense. At the most general level, reflected sound should enhance the direct sound without distracting from it. I don't think I can summarize the topic of room acoustics very neatly, but the bottom line is that the sound you pick up in close proximity to the source is mainly direct sound, but as you pull the mikes back, the proportion of reflected sound increases.

In most practical spaces, it doesn't take all that great a distance for the reverberant (reflected) sound energy to equal and then (if you continue moving farther from the source) exceed the direct sound energy. Our ears and brain decode that for us on an unconscious/habitual level, picking out the direct sound and suppressing excessive reverberation. That's what comes from millions of years of evolution in which those who could localize predators (and/or prey) the most effectively were the ones most likely to survive and reproduce.

But you can get a general idea of the actual, quantitative situation if you go into any reasonable-sized performance space with a single, omnidirectional microphone connected to a preamp or recorder, and listen through headphones (with both ears) to what that one microphone picks up at various distances from any sound source. It's a very revealing experiment, and I recommend that everyone experience this if you possibly can. You can sketch out a boundary line along which a rough equality exists between the amounts of the reflected and the direct sound. This boundary line is nearly always closer to the sound source--sometimes much closer--than most people would guess until they try the experiment.

The farther you go beyond that line, the more the sound field tends to become "diffuse" both in the arrival time and the angle of arrival for each individual sound component that comes in. If you yourself stand in a part of the space where the sound field is largely diffuse, your brain will still localize the sound sources to some extent, because ... two ears, one brain, and millions of years of evolution. And a binaural ("dummy head") recording made at that distance, heard through headphones, will carry that effect across. But a conventional stereo recording, reproduced through loudspeakers, will only preserve a few, very weak cues that the listener's brain can use. So that's too far away for anything but an "ambience"-type recording (again, unless stereo headphones are the sole means of playback--but there are limits even then).

So that's the quantitative "big picture." Qualitatively--when sound bounces off of a room surface (or an object or a living being in the room), the amount of energy that is absorbed (turned into a tiny amount of heat) will vary by frequency. It's a wavelength thing; high-frequency absorption is pretty much a function of surface texture, whereas low-frequency absorption is more a function of rigidity vs. flexibility of the room surface as a whole. Anyway, reflected sound (in most spaces) will have relatively less high-frequency content than the direct sound that produced it, and that's a good thing; reflected sound with prominent content at upper midrange and high frequencies only contributes to harshness, and confuses the stereo image. (That's one reason most engineers who work with omnidirectional microphones favor an off-axis response that rolls off toward the higher frequencies; those microphones work better in more different kinds of recording environments than the generally smaller, "flat all around" types.)

There is also a very important time dimension to reverberance. This is sometimes called "decay time"--the average time it takes for sound to die out in the room after the source stops making sound. Naturally that varies greatly with the sound frequency and the position in the room where you're listening or recording. An auditorium that is designed for maximum speech intelligibility will have a much shorter decay time than a concert hall built for orchestral classical music. The auditorium would also be designed to have much greater absorption at high frequencies--the materials covering the major room surfaces would tend to be textured and soft. (There is no area of overlap between those two sets of requirements, incidentally; any so-called "all-purpose" space can only work equally badly as both an auditorium and a concert hall.)

I dunno; does that get you started, I hope?

The only other thing that I maybe wish I had included would be, how this all interacts with microphone characteristics.

--best regards
Title: Re: M/S audience with SBD feed matrix
Post by: kuba e on September 04, 2018, 06:40:18 AM
DSatz, thank you a lot for nice explanation and for your time to write it. It is useful for me and probably for others tapers like me. I see that acoustic knowledge is very important for recording. This is the inspiration to read more about it in the books.

The only other thing that I maybe wish I had included would be, how this all interacts with microphone characteristics.

I guess roughly what kind of connection it has with microphone characteristics. Please, correct me if I wrote something wrong or inaccurately. The directional pattern influences ratio of direct and indirect sound that is recorded. Omni pattern has the sensitivity approximately the same for all angles and directional patterns have lower sensitivity for off-axis directions. And if we record in mono with one microphone and we would like to have a certain ratio of direct and indirect sound, omni must be placed closer to the source compared with directional patterns. I suppose it's more complicated in stereo recording, because the directional microphones does not point straight to the source, but the principle is the same.

The second characteristic that occurred to me is high frequency responses. If we record back in the room where the reflected sound prevails, it is better to use mics with good high frequency characteristics or to eq recording for heights in post. If I understand it correctly  - On the spot during a concert, our brain favors direct sound at the expense of the reflected. But when we listen to stereo microphone recording in our stereo, this benefit is partly lost and we perceive more reflected sound where high frequencies are missing. So when we record from the back of the room, we should be more observant whether there is need to emphasize the heights.
Title: Re: M/S audience with SBD feed matrix
Post by: Gutbucket on September 04, 2018, 11:32:18 AM
All you young whippersnappers (get off my lawn!) who grew up in the years since stereo became ubiquitous--you have it easy but you may not realize it. You can accept far larger amounts of reflected (room) sound relative to direct sound in your recordings than engineers could in the mono era. Stereo lets the listener's ears and brain sort things out somehow, even in some cases when there's more reflected sound than direct sound.

Put another way, in reverberant spaces, acceptable stereo recordings can be made at greater miking distances than good mono recordings can be. Your brain can't localize anything in a mono recording, so it doesn't take very much ambience to make a mono recording sound muddy; the direct/reflected sound balance is more critical. You also have to pay more attention to the character of the reverberation that you do pick up. Whatever room sound you record in mono had better complement the direct sound or else it can detract, perhaps severely so.

Again, listening for those things is part of the skill set that engineers had to have in the pre-stereo era. Stereo lets you get away with not listening as closely; there's more room for a mediocre sound balance when localization is there for the listener's brain to fall back on.

I've written about this at TS in the past, upon realization that the listening advantages and shift in recording approach of moving from mono to 2-channel stereo is further extended by the shift from two-channel to multichannel surround recording and reproduction, and how its value is more strongly apparent for ambient perspective live music recording than for other types of recording.  Done correctly, surround playback provides sufficient additional cues which allow our specially evolved hearing to more easily separate foreground from background, allowing the ability to "hear around" and "mentally separate and ignore" reverberance and audience chatter from targets of interest which then become more clear and distinct in the "mind's ear" of the listener, making it considerably easier to steer one's attention between particular aspects of interest in the recording. I find that for live-music taping where tapers don't have very much control over recording position placement and program balance, that becomes especially valuable.

With respect to audience-perspective live music recording, that "freedom of listening" naturalness represents the greatest value of surround recording and playback for me.  I feel it actually makes creating acceptable audience perspective recording in a highly ambient situation easier, in the same sense that DSatz describes making a decent 2-channel stereo recording is easier than making a good mono recording.   It takes more gear to do, yet the translation by the listener becomes easier.  If that makes sense, it probably represents the best argument I can make to other tapers for why I pursue surround recording, even though it's not likely to make my posting about it at TS seem any less obtuse or ridiculous to the majority of you folks!  Deep thanks to fellow TS members for your tolerance of all my postings over the years on this kind of arcane stuff few are likely to care about!

Long live stereo.
Title: Re: M/S audience with SBD feed matrix
Post by: Gutbucket on September 04, 2018, 11:32:36 AM
Quote
But when you record in M/S, you really have one foot in the mono era, or maybe even both feet. The "S" microphone has to be placed with the "M" microphone and pick up its own mix of direct and ambient sound. But again that mixture is critical, and it MUST include a substantial helping of direct sound--otherwise the matrixing function (M + S = L, M - S = R) can't possibly produce consistent directional cues for the direct sound. If your mikes are so far back in the room that the "S" mike is overwhelmed with reverberant sound, then the M/S technique is just churning out fake stereo from ambience information.

By the way, since all X/Y methods (including Blumlein!) are equivalent restatements of M/S and vice versa, the same criteria hold true for them.

--best regards

Mono implies a depth dimension via how dry or reverberant a particular sound is with respect to others within the recording.  That depth dimension becomes more clearly discernible in 2-channel stereo, along with the obvious left/right directional differentiation ability which 2-channel stereo provides. The diffuse/pin-point differentiation aspect of 2-channel stereo is just as real and useful as the more obvious left/right differentiation aspects.  I consider it a more basic and more important aspect than left-rightness. 

Likewise, 2-channel stereo is able to imply an immersive environment beyond the left/right playback stage window between the two speakers, which similarly becomes more clearly discernible and mentally-separable in surround.  We can and do work that to our advantage when recording in stereo, and it is arguably more important to do so than for surround (where it becomes easier) just like getting clarity and depth perception correct in a mono recording without everything getting muddied together is more difficult and more perceptually important for good listening results, than it is with stereo.

Even if not ever recording in surround, one can consider these concepts and and apply the ideas in order to make better 2-channel stereo.  How can we make it easier for our highly-evolved ear-brains to parse the direct sound elements from the reverberance and audience reaction elements?  Record in such a way that the reverberance and audience reaction components of the recording are picked up so as to have greater decorrelation between channels, while the primary musical elements from the PA and stage sources are picked up with stronger correlation between channels.  The primary musical elements can then be reproduced with clear left/right imaging stereo cues, while the ambient reverberance and audience are reproduced with more diffuse and cloud-like stereophonic qualities.  In that way those different elements sort of remain out of each other's way so as to allow us an increased ability to focus on each part distinctly.

Well decorrelated ambience and audience is not left/right pin-point type of stereo, yet is certainly "real" in a natural hearing sense and not "pseudo stereo".  It is a different type of stereo, and the two work together to paint a more convincing picture.  Recording in ways such that much of the ambient reverberence and audience reaction is sufficiently decorrelated between channels makes it easier to differentiate sounds arriving from the band in front, reproduced so as to appear within the imaginary window framing the performance within the space between the speakers, from the sounds arriving from all other directions.  It's not doing so by actively reproducing the sound outside that stereo window in a discrete way like multichannel surround playback does, yet still conveys it in a way that allows our hearing mechanism to differentiate it more clearly.