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Author Topic: Understanding LCR/LR+M Mixing  (Read 17893 times)

Patrick Tracy

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Re: Understanding LCR/LR+M Mixing
« Reply #10 on: January 02, 2007, 03:42:34 pm »

Jeremy Johnston wrote on Tue, 02 January 2007 09:28

As I understand it, the first true stereo systems developed used three channels; Left, Center and Right.


Two- and three-channel stereo were both proposed quite early.
Jeremy Johnston wrote on Tue, 02 January 2007 09:28


They discovered that a "sweet spot" existed between the left and right loudspeakers that created a "phantom image" so that the center loudspeaker wasn't needed and voila you have what we call "stereo" today.

I think this was more of an excuse for using the simpler two-channel method and avoiding the expense of an extra signal path. Plus, audiophiles were using one speaker cabinet and convincing then to use three seemed like too much of a challenge.

Dave Dermont

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Re: Understanding LCR/LR+M Mixing
« Reply #11 on: January 02, 2007, 07:13:41 pm »

LCR is often used in House-of-Worship systems for speech in much the same way it's used in theatre to anchor dialog.

Yes, proper system installation is very important.

You can use smaller consoles that have a 'Center' or 'Mono' bus, as long as there is a way to assign to that bus, and only that bus. Some consoles only derive the mono signal by summing L&R.

Also, different consoles built with LCR in mind handle it differently. Midas calls is "SIS" for "Spatial Image System", where the Pan goes from left, to center, to right. In this system, things panned to the center are ONLY in the center. They don't go to Left or Right. It does this when 'SIS' is engaged. When "SIS" is not engaged, it pans normally.

The Soundcraft MH works like this too, but they just call it "LCR". I guess they did not feel the need to make up a new term to confuse people.

The Allen & Heath ML series has a system they call "LCR PLUS". This system has an additional "blend" control that "pans" signals from L&R to Center. (or in A&H's case, Centre) It looks like the photo below.

index.php/fa/7188/0/

Inter-M has a console they call Kensington that uses this type of system. I was involved with Inter-M and the Kensington before they moved US operations from PA to CA. This is why I am so well schooled in LCR console offerings.
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Mats Fagerkull

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Re: Understanding LCR/LR+M Mixing
« Reply #12 on: January 02, 2007, 11:41:15 pm »

Dave Dermont wrote on Wed, 03 January 2007 01:13


Also, different consoles built with LCR in mind handle it differently. Midas calls is "SIS" for "Spatial Image System", where the Pan goes from left, to center, to right. In this system, things panned to the center are ONLY in the center. They don't go to Left or Right. It does this when 'SIS' is engaged. When "SIS" is not engaged, it pans normally.



Just a quick question, is the "SIS" acronym really a product of MIDAS origin ? I know DDA was using this and thought MIDAS (as a sibling) might have adopted it when that brand was discontinued. Am I totally wrong here or what?

/mats
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Brad Weber

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Re: Understanding LCR/LR+M Mixing
« Reply #13 on: January 03, 2007, 11:58:39 am »

It sounds a lot like how the DDA CS3 and CS8 consoles worked (the QII as well if I remeber correctly), assigning each channel and group as either L/C/R or L/R.
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Tom Young

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Re: Understanding LCR/LR+M Mixing
« Reply #14 on: January 04, 2007, 10:41:35 am »

I know we have discussed the basic requirements for LCR here on LAB befor. Try some other searches.

Jim Brown has at least one reference paper for proper LCR ldspkr system design and I think he also defines how the electrical design of the console must be, as well.

see: www.audiosystemsgroup.com

Crest consoles and now APB Dynasonics not only have LCR done correctly.... they also have several other innovative design features.  Just FYI.
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Tom Young
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Briand Parenteau

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Re: Understanding LCR/LR+M Mixing
« Reply #15 on: January 12, 2007, 10:19:06 am »

I'd like to add another variable to this discussion.  It pertains to the differentioan on what is more specifically known as a LCR Cross Matrix system.  I have added a couple of links to AES White Papers for this, so that everyone can read and understand the complexities of this design.  The reason I'd like to bring this up, is that the design is a bit different and this thread has really not addressed it.  Any installers out there may be more aware of this.  It is most often found in churches.

I have encountered a couple of these systems, they are a different animal of sorts.  I'd like to hear from people that have used these and what their respective experiences were.  Note, as written in the tech papers, that if you do not set up your bus assignments specifically as detailed, you will end up with a mess.  Lots of time smearing and phase issues.  I have a number of issues with these designs, but I'll save that for a later response.

Please follow the links below to read up on LCR Cross Matrix design and mixing principles

http://www.sound-technology.com/Research2/Breshears%20multic hannel%20design%20for%20AES-98.pdf

http://www.sound-technology.com/Research2/Multichannel%20Mix ing%20AES01.pdf

B. Parenteau
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Michael 'Bink' Knowles

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Breshears LCR Cross Matrix multichannel mixing
« Reply #16 on: January 12, 2007, 11:37:44 am »

Great swerve topic! I think if I were to encounter a system like this I'd make sure to plan my miking carefully and use the L+R elements of the speaker system to best effect by doing things such as hard panning two different mics on the same source. For instance, I'd be interested in trying out a mic on guitar amp front sent to Left and another one polarity flipped on guitar amp back sent to Right. Or the same thing with top and bottom snare mics. Or Don Henley's dual tom miking system where he has a Beta98 and an MD421 on each tom. Of course piano would provide a wealth of fun tricks...

Not many desks can deal with this kind of matrixing with delay. Have you seen it accomplished with an external matrix?

-Bink
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Michael 'Bink' Knowles
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Michael 'Bink' Knowles

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Re: Breshears LCR Cross Matrix multichannel mixing
« Reply #17 on: January 12, 2007, 11:39:24 am »

BTW, Briand, this subject is totally LAB Classic.  Cool

-Bink
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Briand Parenteau

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Re: Breshears LCR Cross Matrix multichannel mixing
« Reply #18 on: January 12, 2007, 12:27:31 pm »

Thanks Bink,

This topic opens up a pretty controversial discussion in my opinion.  Maybe it's just because I have a beef with the design!  Anyway, the way that I have seen it implemented is ONLY with external matricing via multiple audio processors.  Essentially, every box needs discrete processing and amplification. The install contractor takes L/C/R busses off the desk than does all the matricing at the head end before the amps with DSP.

There are a number of complications in running this sort of rig and being able to reproduce consistent results, especially in an install when you have various sound tech's operating the desk.  A simple stereo source like a CD or VTR will not sound right unless you use a Dolby processor! FX returns will be impacted by this as well.  I have operated one of these systems and the results were less than impressive, in my experience.    I am keeping an open mind though and going back for another go at it this weekend.

I am going to paste some of my thoughts below, that I presented to an installer (in blue) who has done a lot of these systems. These thoughts were location specific, my reflections on a system that I utilized installed by his company.  He never formally responded.  Also please see the note (in red) about CD playback. This comes from the engineer who submitted the AES papers.

CD PLAYBACK-
Due to the speaker locations in many of these systems, the stereo playback of a CD through theLeft and Right speakers can cause some problems, particularly at the sides of the room.Differences in arrival times of the direct sound for percussive instruments when sourced through both speakers creates a flanging or phasing effect that can be quite annoying. Instead of just playing back a CD through the Left and Right channels, it is best to use a Dolby Pro Logic processor that will take a stereo input and create left, center and right channels. This created center channel signal provides a discrete mono source for all of the instruments andvocals that would otherwise be reproduced through the left and right channels.


I have been studying up on the LCR cross matrix theory and implementation by way of a number of AES White Papers.  Although this is a pretty cool approach and it can work, I think there are a couple of big issues with reproducing live bands in a venue where there are going to be variable changes.   As noted(see white paper excerpts)to really get the stereo imaging to work you need to double mic any source that you desire to be reproduced in the stereo field.  Also, the buss assignment is critical in order for this system to work as designed.

There has to be strict uniformity in how the band is mic'd up and bussed, in a way that does not lend itself to changes.  This is rigid and okay for an environment that has little change, but as soon as you introduce change in the form of different instrumentation, visiting bands, varying sound engineers, etc...  the design becomes extremely susceptible to failing and producing a multi-source, multi-arrival nightmare akin to what I experienced when first listening to the system.  Even at it's best the amount of audio sources (loudspeakers) that exist and their respective locations create an environment where there is a lack of uniformity in the listening area.  The shear number of sources, even with the proper DSP, are still going to lend to a generous amount of comb filtering and lobing, especially in the near field extremes prior to reaching the delay zones.  

B. Parenteau
Showmix

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Tony "T" Tissot

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Re: Understanding LCR/LR+M Mixing
« Reply #19 on: January 12, 2007, 01:16:22 pm »

No arguments with the above responses -

If I were to put this in very simple language:

- For speaking / singing parts in the theater (particularly musical theater)   makes it seem less like the speaking / singing parts are amplified. (Precedence effect - slight delay for height). As in "we all know it's amplified" - but we want to preserve the illusion that it is not amplified. Center cluster achieves this.

- A "true" C channel - The signal to the "C" has to be separately derived. I used the group matrix function to get that or group assignments. The vocal mics do not deliver any signal to the L and R channels and vice versa.

- C is a completely discrete channel with full coverage. If you have delay or balcony fills it's also fully discrete from the L and R.

- Orchestra, EFX typically just to LR.
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MNGS
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