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Author Topic: m/s --room reverberation and large choir recording questions  (Read 9422 times)

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Offline 2manyrocks

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I've never recorded in m/s and am having a bit of trouble figuring out how to ask the right questions.

Is it true that a hypercard pattern can be had from pairing a figure 8 with a card?  And it's adjustable in post recording?

Also read that one of the issues with m/s is that in recording a large choir, the center can be overdone compared to the edges of the choir?  Do you overcome this with flanking microphones? 

So m/s would be really good for a smaller ensemble, but not so much for a larger one of say 200 voices?



Offline voltronic

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Re: m/s --room reverberation and large choir recording questions
« Reply #1 on: May 09, 2015, 08:19:13 PM »
Now it's my turn to tell you to contact Boojum - he has been doing the center M/S with flanking omnis more lately from what he tells me.

I'm not sure about your hypercard comment.  What I can tell you is that with M/S recording in general, yes you can adjust the "dry/wet" balance in post.  I would recommend that you do not record through a M/S matrix and instead just keep them separate to make balancing in post easier. 

EDIT: I see you are asking about the M/S mode in the 70D.  Some pres and recorders have a M/S decoding matrix built in, for example Schoeps VMS preamps.  While this can be nice, my personal preference is to record the mid and side mics as separate mono tracks (or a hard-panned stereo track) and then decode them later in the DAW, either with a M/S plugin or just making your own matrix, where you duplicate the side (fig8) track and phase-invert the duplicate.  The center (card) is center panned, but the mid (positive phase) is panned hard left while the mid (inverted phase) is panned hard right.  See tracks 4-6 in the screenshot below.

As far as the large / small choir: I've used my colleague's Schoeps M/S setup several times to record his large (250+) and small (40-50) choirs, and I don't think it the size of the group makes a difference one way or another, at least from the relatively far back distances I record.  It's more the other problem - you can get too much hall sound, but you can easily dial that back by lowering the side tracks in your DAW.  I have a few mixes of the small choir I'm mentioning with the sides equal to the center, then dropped by 3 and then 6 dB I could post to illustrate this.
« Last Edit: May 09, 2015, 08:53:02 PM by voltronic »
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Offline voltronic

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Re: m/s --room reverberation and large choir recording questions
« Reply #2 on: May 09, 2015, 09:08:45 PM »
Here's a link to the project I'm mentioning.  I did not record this personally, so I have no idea about mic placement or distance - it was just sent to me for mixing.  The cardioid and fig8 were recorded as separate mono tracks at my request.
Schoeps MK4/MK8 > CMC5 > Zoom H6.  40-50 voice HS chamber choir in a medium-sized church.  This was for a local radio Christmas carol school choir contest, and sadly they chose a far inferior choir to this one to put on the air!
https://www.dropbox.com/sh/1qdzq25muzg20j0/AADznIP4w3VNc_JdvCzPs4RBa?dl=0
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Offline 2manyrocks

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Re: m/s --room reverberation and large choir recording questions
« Reply #3 on: May 09, 2015, 10:17:58 PM »
Nifty neato.  Seems like M/S offers the choice of cutting back on the room by cutting back on the S with a tradeoff of less fullness in the sound. 

When you record the 250 voice choir, how far back are you placing the mics?  Is m/s his choice of mic configuration?

How do you like m/s for choral recording v. what you're trying with the 4 mic array?

Offline voltronic

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Re: m/s --room reverberation and large choir recording questions
« Reply #4 on: May 09, 2015, 10:44:27 PM »
Nifty neato.  Seems like M/S offers the choice of cutting back on the room by cutting back on the S with a tradeoff of less fullness in the sound. 
Yeah, that's pretty much it.  But I think if you add omni outriggers as Boojum and others have done, you may be able to dial back the side of the M/S pair and add a different kind of hall ambiance back with with flanking omnis.

Quote
When you record the 250 voice choir, how far back are you placing the mics?  Is m/s his choice of mic configuration?
Well I only get to record that choir once a year, and the Schoeps M/S pair belongs to the choir's director.  Yes, that's his choice as they're the best mics he has.  They're placed in the only location I'm allowed by the video crew, which is halfway back in a large auditorium, fairly close to dead center.  It actually is probably the best place to record in there being that there are some groups on stage and others on the pit, so for an overall balance of the concert it works well.  Here's a sample of that big choir from last year's concert, recorded in that location with just the CM3s in NOS.  They really crank up the volume after 3:30.  The audience noise is because this is accompanying a senior slideshow.  Unfortunately I don't have a copy of the M/S recording to compare.
https://www.dropbox.com/s/mbhh379fabxh37f/Bridge%20Over%20Troubled%20Water.mp3?dl=0

Quote
How do you like m/s for choral recording v. what you're trying with the 4 mic array?
It's hard to tell - the two setups sound completely different.  Since I only get my hands on that M/S rig once or twice a year it's difficult to make a direct comparison, and sometimes I don't even get to hear those files as those mics go to his recorder instead of mine.  I like that the 4-mic array allows some balancing of the sound in post like M/S does, although less drastically changing the sound.  In a very reverberant space like in the M/S samples I posted, you can sometimes make it sound anywhere from a cardboard box to an airplane hangar.
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Offline 2manyrocks

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Re: m/s --room reverberation and large choir recording questions
« Reply #5 on: May 10, 2015, 01:58:27 PM »
A competent video crew could shoot around a mic stand. 

Where is the video crew pulling their audio feed?
« Last Edit: May 10, 2015, 02:06:43 PM by 2manyrocks »

Offline voltronic

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Re: m/s --room reverberation and large choir recording questions
« Reply #6 on: May 10, 2015, 02:43:40 PM »
A competent video crew could shoot around a mic stand. 

Where is the video crew pulling their audio feed?
First, it's a school and we have a student TV studio.  They use multiple cameras but are fixed on tripods.  If my stand were down in the pit, it would be in the way of the conductor for smaller ensembles that perform there and would be right in the shot for any of their 4 cameras.

Their audio is from an AT X/Y in the middle of the large choir just in front of the conductor, and sometimes they just set up one SM58 or similar on a stand next to one of the cameras.  Their videos sound awful, and there are professionals running this.  The director likes to only deal with mono.  I have offered many times to give them a stereo feed off of my FP24 or recorder.  Sometimes I dropbox the TV people my unedited recording for them to replace their audio with, but they have used it exactly once.  I may not be a professional recording engineer, but even when I was just recording with CA-14s into my M10 my audio was light years better than theirs.  It's very frustrating.
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Offline 2manyrocks

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Re: m/s --room reverberation and large choir recording questions
« Reply #7 on: May 10, 2015, 02:57:58 PM »
How is the video ultimately used? 

I assume then you have a director primarily concerned with how his video looks? 

We have a theater director focused on appearances.  His set changes make every play run twice as long as the script. 

Offline DSatz

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Re: m/s --room reverberation and large choir recording questions
« Reply #8 on: May 11, 2015, 07:56:03 AM »
With standard (two-microphone) M/S, you can adjust the amount of reverberation in the eventual L/R stereo mix. But you can only adjust it relative to the amount of reverberation that the "M" (forward-facing) microphone is picking up--which in turn depends on its location, its pattern, and the room. If the "M" microphone is placed too far back for its pattern and the room characteristics, then even if you leave the "S" signal out of the mix completely (giving you a mono recording), you will still have too much reverberation in the recording.

M/S can't compensate for overly distant (or for that matter overly close) placement, for the choice of an overly broad (or for that matter overly narrow) pattern for the "M" microphone, or for overly reverberant (or for that matter overly dry) room acoustics. When you go back to the reason it was invented in the early 1950s, when stereo LPs and FM broadcasts were first being planned, it is basically a method for making a normal mono recording (the thing that 99% of all listeners would hear back then) that also yields a stereo version. The stereo version would offer a greater net amount of reverberation--but that would be balanced by the listener's ability to localize sound sources in the horizontal plane, such that the overall clarity of the mono and stereo recordings would be subjectively more or less equivalent if you made good miking and matrixing decisions.

Being forced to place your microphones a considerable distance from a wide stage has its good and bad sides. The good side is that the distance tends to reduce any excess emphasis or focus on the performers at the front and center of the stage, which you might have with closer miking. The bad side is the loss of immediacy and clarity, and the inclusion of room sound that may not be pleasant in character. To some extent you can compensate by using an "M" microphone with greater directivity (e.g. for Schoeps, an MK 41 instead of an MK 4); the difference between a cardioid and a supercardioid is only moderate rather than night-and-day, but it can definitely be worthwhile.
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Offline 2manyrocks

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Re: m/s --room reverberation and large choir recording questions
« Reply #9 on: May 11, 2015, 10:09:53 AM »
Thank you for your helpful explanation. 

Two general followup questions.  Do you find m/s a suitable configuration for recording large choirs when you are free to place your mic stand anywhere or do you prefer another configuration?

Are there other mic configurations that could be more suitable for recording large choirs when one is forced to place the main mic stand at a distance?  A pair of mk41 in ortf for example?

Offline Gutbucket

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Re: m/s --room reverberation and large choir recording questions
« Reply #10 on: May 11, 2015, 10:45:44 AM »
Is it true that a hypercard pattern can be had from pairing a figure 8 with a card?  And it's adjustable in post recording?

Yes.  But it will only produce a crossed hypercardioid pattern at one point along the mix ratio continuum, resulting in one particular virtual microphone angle.  Both the virtual microphone patterns and angle between them change together as you vary the M/S mix ratio. With a mix ratio of 100% Mid, 0% Side, the virtual microphone output is two forward facing cardioids with no angle between them.  With a mix ratio of 0% Mid, 100% Side, the virtual mic output is two sideways pointing figure-8s.   So if your mix ratio is mostly Mid, you get a virtual microphone pattern closer to cardioid shaped without much angle between them.  If mostly side, the virtual mic patterns are closer to 8-shaped, with a large angle between them.  At mix ratios somewhere between those, you get virtual crossed hypercardioids at one particular angle and crossed supercardioids at a narrower angle.

Quote
Also read that one of the issues with m/s is that in recording a large choir, the center can be overdone compared to the edges of the choir?  Do you overcome this with flanking microphones? 

So m/s would be really good for a smaller ensemble, but not so much for a larger one of say 200 voices?

The first question is easier to answer since it's simply a technical one.  This part is more one of personal preference.  Here's my feelings on it, but they are only my own preference- 

When I listen to a large choir, the auditory impression I get is of a large, massed, big, spacious and enveloping sound, many voices blending together.  I usually want the recording to convey a similar auditory impression, so I'm likely to use a microphone technique which is good at conveying those aspects, and I'm likely use spaced mic techniques.

I don't care much for the monophonic reverberation component of most coincident techniques, which just doesn't sound very natural or good to me in a subjective sense, so I consider M/S as more of a useful modification of other techniques rather than a primary stereo configuration.  With a few exceptions, I'm less a fan of coincident techniques used on their own than spaced techniques used on their own.  So I start from spaced techniques and use coincident ones to improve on that when appropriate, and I may end up with a M/S pair in the center between a spaced pair.  Conceptually I'm starting with a wide spaced pair as the staring point, often adding a center microphone to solidify the center and provide presence rather than conceptually starting from a center coincident pair and adding flanking microphones.  Then rather than just the single center mic, I might also add a coincident sideways facing figure-8 to form a M/S pair as a way to adjust with the breadth of that center presence contribution.  That way, when listening back, I can adjust both the balance between the spaced mic pair and the center mic, and also the width and imaging of the center for best effect and a seamless blend across the playback stage.

So when I use M/S, it's usually to have the option of adding some width to a mono channel later.  I might want to add a bit of width to a mono spot mic, or to the center microphone contribution of a 3-mic stereo array.  But that's just what works for me.
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Offline Gutbucket

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Re: m/s --room reverberation and large choir recording questions
« Reply #11 on: May 11, 2015, 06:08:40 PM »
I'd like expand a bit more on what I posted above, to address a basic issue of the 'adjustable' aspect of the M/S stereo microphone technique, which I find is not generally well understood.

One of the frequently cited advantages of M/S is that the pickup pattern and angle between the virtual microphone pair are adjustable after the recording has been made.  That's true, but as explained above the relationship between pickup-pattern and angle is always locked, and you cannot change one of those things without also changing the other at the same time.  The real problem with that is not so much that the relationship is locked, even though it would be nice to be able to adjust angle and pattern separately.  The bigger problem is that the locked relationship between the two is the inverse of what we'd really like it to be.   At least if stereo is the primary intention of the recording rather than mono.

[self quote from my previous post above]
With a mix ratio of 100% Mid, 0% Side, the virtual microphone output is two forward facing cardioids with no angle between them.  With a mix ratio of 0% Mid, 100% Side, the virtual mic output is two sideways pointing figure-8s.   So if your mix ratio is mostly Mid, you get a virtual microphone pattern closer to cardioid shaped without much angle between them.  If mostly side, the virtual mic patterns are closer to 8-shaped, with a large angle between them.  At mix ratios somewhere between those, you get virtual crossed hypercardioids at one particular angle and crossed supercardioids at a narrower angle.

In terms of stereo, it would be much better if it worked the opposite way, so that the pickup patterns became more figure-8 like as the angle between virtual microphones became smaller, and more cardioid-like as the angle between microphones became greater.   That's the basic relationship between angle and pattern which we play off of each other in selecting appropriate stereo pair configurations, ignoring the additional aspect of spacing between the microphones of course since M/S is always coincident.

Because that relationship is locked in the inverse of what we'd like, M/S usually only really works well at one setting within in a rather narrow range of it's mix-ratio 'range of adjustment' for a stereo output.  The often touted advantage of being able to flexibility adjust angle and pattern after the recording has been made isn't really as great as we'd like it to be when the application is a main stereo pair.  If it works well near that one optimum mix-ratio great, but it's not because of any 'M/S adjustablility', it's because that one specific angle/pattern combination is appropriate for the recording situation.

That's not a problem when using M/S as a way of adding a bit of optional stereo width to a mono channel, where the goal isn't achieving a great stereo image on it's own, but rather smoothly and predictably adding stereo width and dimension to a mono channel without corrupting the mono channel or introducing phase complications.
« Last Edit: May 11, 2015, 06:15:04 PM by Gutbucket »
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Offline hi and lo

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Re: m/s --room reverberation and large choir recording questions
« Reply #12 on: May 11, 2015, 06:58:32 PM »
Thank you for your helpful explanation. 

Two general followup questions.  Do you find m/s a suitable configuration for recording large choirs when you are free to place your mic stand anywhere or do you prefer another configuration?

Are there other mic configurations that could be more suitable for recording large choirs when one is forced to place the main mic stand at a distance?  A pair of mk41 in ortf for example?

I can only speak from my limited experience seeing others experiment and listening to the results, but in my opinion M/S is junk for what we do and I would never bother with this silly configuration. It's a compromise in every sense of the word.

M/S was developed, in-part, for mono-capability and I challenge anyone to convince me why this would ever benefit the average concert recordist. I never listen to my recordings via mono playback and can't think of a reason why I ever would.

Moreover, I'm not a fan of coincident recording in general, i.e. X-Y. Maybe it's just me, but the timing delays of near-coincident techniques are very important to my ears and when those are gone, the recording suffers dramatically.

Offline voltronic

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Re: m/s --room reverberation and large choir recording questions
« Reply #13 on: May 11, 2015, 07:11:53 PM »
Discussions like this are why I come here. :)  I enjoy listening to the recordings of my friend's MK4/MK8 setup, but I think DSatz and Gutbucket may have explained why I've felt that, especially at a significant distance, I am preferring the sound of spaced omnis or near-spaced directional mics.  I hadn't considered that M/S was developed as a "mono with benefits" technique.  In a nice acoustic like the sample I posted, I think the M/S setup sounds good but it's more difficult to get a "realistic" sound, at least for me.  Next Thursday I will record that large choir again, and I hope to have the feed from the M/S to compare to my omni / card tracks.

DSatz: Totally on the opposite end of your suggestion of using an MK 41 in place of an MK 4, do you have experience with using an MK 2H in that application?  I have heard of using omnis as the mid mic in certain situations (which makes some things you've spoken of worse but others better), and the 2H seems like it could be a good compromise for more distant placement.
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Offline voltronic

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Re: m/s --room reverberation and large choir recording questions
« Reply #14 on: May 11, 2015, 07:26:38 PM »
Thank you for your helpful explanation. 

Two general followup questions.  Do you find m/s a suitable configuration for recording large choirs when you are free to place your mic stand anywhere or do you prefer another configuration?

Are there other mic configurations that could be more suitable for recording large choirs when one is forced to place the main mic stand at a distance?  A pair of mk41 in ortf for example?

I can only speak from my limited experience seeing others experiment and listening to the results, but in my opinion M/S is junk for what we do and I would never bother with this silly configuration. It's a compromise in every sense of the word.

M/S was developed, in-part, for mono-capability and I challenge anyone to convince me why this would ever benefit the average concert recordist. I never listen to my recordings via mono playback and can't think of a reason why I ever would.

Moreover, I'm not a fan of coincident recording in general, i.e. X-Y. Maybe it's just me, but the timing delays of near-coincident techniques are very important to my ears and when those are gone, the recording suffers dramatically.
When you say "what we do", remember that some of us here are Team Classical and in that context have enjoyed the benefits of M/S.  For amplified music, especially with crowd noise, M/S is probably very counterproductive.  I agree with your first sentence, except I would replace "M/S" with "X/Y".  I think M/S has the potential to sound good in far more situations than X/Y, which in my experience rarely sounds good even with good acoustics, quiet hall, etc.  I think manufacturers are to blame for promoting X/Y to the point where so many people think that's just "what you do" to record in stereo.  I'm not talking about cheap built-in mics, but more things like the Rode NT4.  I wish they had emulated the Schoeps 64G instead - the cost wouldn't have been that different.  While ORTF is not the right choice all the time either, I think percentage wise you're going to succeed more often than fail with it versus X/Y.
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