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Author Topic: Understanding LCR/LR+M Mixing  (Read 17892 times)

Dave Heath

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Understanding LCR/LR+M Mixing
« on: January 02, 2007, 07:49:56 am »

Hi guys,

I have a question (see notes) about "LCR" and "LR and/or M" and how they work.
As my career as a live sound engineer picks up, I have started to be allowed to play with larger desks in larger venues and increasingly they are having these 3 faders for the master out.

Now at the moment I am only working in venues that just have a Left and Right speaker setup and so the C or M fader doesn't get used, but I can only imagine that these desks have this control for a reason and that one day I might need to know about it.

So my question is, would someone please be kind enough to explain how it works and when I would use it? (with main focus on FoH, but interested in Mons too)

Many thanks for all who have managed to read this far down and even great thanks in advance to all who reply.

Dave Heath


Examples of desks I have encountered LCR or LRM (enter newbie-big-head-mode)
A&H GL2800
Soundcraft MH4
Midas Verona

Note to the nice moderators:  If this is in the wrong section, I apologies, please move this thread to where it is best. (hopefully not the basement)

Note to the search police: I did have a search here and in google, but all I can find are posts/articles saying that LCR mixing exists and is possible with this or that desk.
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Dave Heath

Mike {AB} Butler

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Re: Understanding LCR/LR+M Mixing
« Reply #1 on: January 02, 2007, 09:09:17 am »

Dave,
I love systems with LCR, as it gives me the ability to separate stuff, such as instruments from vocals. My usual Modus Operandi is to put vocals in the Center, and place instruments in L/R (subs are still always Aux-fed).
My reason for this is simple. I have actually had cases in  using only a L/R configuration where vocals were just so-so.  Moving them to a center cluster - much better in terms of overall sound quality.
People can say line array all they want.. but for me the real bee's knee's is in a LCR system..
HTH,
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Mike Butler,
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Dascott Technologies, LLC

Eric Dodson

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Re: Understanding LCR/LR+M Mixing
« Reply #2 on: January 02, 2007, 10:10:05 am »

Mike Butler is right on with this.
LCR rigs in theaters or on the road give you the ability to seperate the vocals and get more "acoustic imaging" on your stage.
What I find myself doing when I'm mixing a band on a LCR rig is not only putting vocals in the center cluster, but when someone is soloing like a guitar or keyboard part, I'll mix that in to get the same effect.
I always have a smile when I encounter a LCR rig. The proper use of one can really improve you mix to the audience.
Cheers.
Eric Dodson
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Carey Davies

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Re: Understanding LCR/LR+M Mixing
« Reply #3 on: January 02, 2007, 11:21:06 am »

Dave Heath wrote on Tue, 02 January 2007 12:49

Now at the moment I am only working in venues that just have a Left and Right speaker setup and so the C or M fader doesn't get used, but I can only imagine that these desks have this control for a reason and that one day I might need to know about it.

So my question is, would someone please be kind enough to explain how it works and when I would use it? (with main focus on FoH, but interested in Mons too)


Hi Dave, good question.

LCR rigs can give you much better coverage and intelligibility, but only if properly installed and set up. This requires three speaker setups, one either side of the stage as you would find with the typical LR system, and one in the centre, usually hung to get it out of view of the action on stage, and to ensure enough throw to the rear of the room.

The success of these systems relies on all speakers being heard equally by all listeners. The centre (C) speaker is as important as the sides and not simply a fill for the front rows as is the case in many LR equipped venues. This can present the installer with several challenges, and the venue with a meaty budget requirement. For this reason it is mostly the top end venues and large scale touring rigs that offer LCR.

Many consoles provide the capability to run different types of multi-speaker rigs including LCR, independently driven sub, or added fills. The GL2800 provides 3 master faders, L, R and M. Although you can't pan between L C and R, you could assign your prime sources such as vocals and kick to the C speakers by routing to M, and the other instruments to LR. Even if you do not have an LCR system you could use the M output to feed the subs, for example kick and bass, to clean up the mix by preventing unwanted low frequency pickup from the other mics getting to the subs. In monitor mixing, consoles like the 2800 can reconfigure the M master as the engineer's wedge speaker controller, leaving the LR masters available for side fills.

Hope that makes sense. Let us know if you weant more chat on this.
All the best,
Carey
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Scott Van Den Elzen

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Re: Understanding LCR/LR+M Mixing
« Reply #4 on: January 02, 2007, 11:28:42 am »

This topic is intriguing...  I have a relatively small rig and cover relatively small rooms.  Thus, I have never been in a situation where LCR is useful (or really possible.)  

Can you fill in some blanks for me?  Does the center cluster cover the same area as LR?  I'm assuming the center cluster has to cover the whole room if vocals will only be present in the center mix.  So, where frequency overlap occurs between vox and instruments, how is comb filtering avoided?
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Jeremy Johnston

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Re: Understanding LCR/LR+M Mixing
« Reply #5 on: January 02, 2007, 11:28:53 am »

Hi dave,

As long as each loudspeaker (array, cluster etc) can cover the entire room, then separating things across the sources will allow a cleaner mix and better "Stereo".  As I understand it, the first true stereo systems developed used three channels; Left, Center and Right.  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.  But that's only in one seating position.  If you have a properly designed LCR system to mix on you can create a stereo image for a much larger percentage of the audience.

Then there's the whole issue of speech intelligibility. I know this is mostly a music performance audio forum, but some of us mix in churches or at talking head events and the true facts are that speech intelligibility is important.  The better people can understand what's being communicated the more likely they are to respond to whatever is being said.  A single center source that simply amplifies the speech is less distracting to a listener. Multiple sources that conflict with one another cause that "whooshing, phasing" sound when you move your head or make you listen to a talker from one side of the room while seeing him (or her) on the other side of the room.

The center system can allow excellent speech intelligibility and localization while the stereo system offers good stereo imaging for music. A properly designed LCR or LR+M system can allow both excellent music AND excellent speech in those events where you need both.

Jeremy J
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Yngve Hoeyland

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Re: Understanding LCR/LR+M Mixing
« Reply #6 on: January 02, 2007, 11:53:13 am »

This is interesting. I've done a few LCR productions but mainly in theatres where the dialogue usually goes center for intelligibility  reasons.

I'm just thinking of the practical side of things here - if say for  a music-only production you want to fly a center cluster but your front truss is fairly low so you can't really put a whole cluster there or the people on stage will be looking straight into the back of your C fill? Is it worth just putting a single box or two up there? Any experiences on this? I'm specifically thinking of smaller "semi-linearray" systems such as the JBL VRX etc. which have quite wide dispersion angles (120)?

Anyone tried this out for -1000 seaters?
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Brad Weber

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Re: Understanding LCR/LR+M Mixing
« Reply #7 on: January 02, 2007, 12:11:10 pm »

Since no one else has apparently addressed it, you noted the two variations on this.  In L/C/R there are three output buses and the signal routing to these is via panning.  As you pan a signal from left to center to right it literally pans across the three outputs.  At center the signal goes just to the center output with no left or right output, full left and only left output and between left and center splits the signal between the left and center outputs.

In L/R + Mono you still have thee output buses but whether something is L/R or mono is a result of an output bus assignment rather than a pan.  You can assign a signal to either or both outputs.  If a signal is assigned L/R and panned center, it comes equally from both left and right and not from the mono output.  A mono send is just that and pan does not affect it.

L/R + Mono is often used to have a mono center speech speaker/cluster/array and then split left and right stereo speakers/clusters/arrays.  Using a single point for the speech reinforcement can reduce the timing and localization issues that would result if the same signal is reproduced from multiple locations.  At the same time, the L/R arrangement allows for greater stereo separation for stereo playback.  Since the center speaker/cluster/array is typically used primarily for speech sources, the speaker array components used are often selected based on voice reproduction (maybe a 12" woofer and usually no sub) while the left and right speaker array components are typically selected based more on music reproduction.

L/C/R also uses three speakers/clusters/arrays and allows for greater flexibility in imaging.  However, in many system panning a single channel source across multiple speakers can result in combfiltering and other anomalies, so these systems have to be designed with this in mind.

In both approaches, for the system to work properly the left, center and right speakers/clusters/arrays must each properly cover the listener area, as others have already noted.

As far as vox and music causing combfiltering, you get summation and cancellation at different frequencies any time you mix two signals.  However, combfiltering in speaker systems is normally caused by the same signal coming from multiple sources such that those signals arrive out of phase with one another.  This issue affects the original signal component rather than how that signal combines with different signals.

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Mike {AB} Butler

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Re: Understanding LCR/LR+M Mixing
« Reply #8 on: January 02, 2007, 03:23:13 pm »

As Brad points out below, comb filtering is most common when the SAME source material appears from different speakers. Different sources from different speakers don't negate each other as badly.. hence, the intelligibiity advantage.
Regards,
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Mike Butler,
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Dascott Technologies, LLC

Mike {AB} Butler

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Re: Understanding LCR/LR+M Mixing
« Reply #9 on: January 02, 2007, 03:34:59 pm »

Carey Davies wrote on Tue, 02 January 2007 11:21



LCR rigs can give you much better coverage and intelligibility, but only if properly installed and set up. This requires three speaker setups, one either side of the stage as you would find with the typical LR system, and one in the centre, usually hung to get it out of view of the action on stage, and to ensure enough throw to the rear of the room.

The success of these systems relies on all speakers being heard equally by all listeners. The centre (C) speaker is as important as the sides and not simply a fill for the front rows as is the case in many LR equipped venues. This can present the installer with several challenges, and the venue with a meaty budget requirement. For this reason it is mostly the top end venues and large scale touring rigs that offer LCR.

Many consoles provide the capability to run different types of multi-speaker rigs including LCR, independently driven sub, or added fills. The GL2800 provides 3 master faders, L, R and M. Although you can't pan between L C and R, you could assign your prime sources such as vocals and kick to the C speakers by routing to M, and the other instruments to LR. Even if you do not have an LCR system you could use the M output to feed the subs, for example kick and bass, to clean up the mix by preventing unwanted low frequency pickup from the other mics getting to the subs. In monitor mixing, consoles like the 2800 can reconfigure the M master as the engineer's wedge speaker controller, leaving the LR masters available for side fills.


Carey,
I think you are correct this would be costly to do as a rental system. But, as an install, I have installed 3 low budget LCR (or LMR) systems - provided the Center gets used for vocals, and the lows only get reproduced through subs. Typically smaller, less expensive speakers are needed for Vox reproduction.. as long as they have the SPL to keep up.. which is NOT true of the instrumental parts, in nearly all cases. As far as the console.. any console which has a switch to disconnect a subgroup from the mains.. AND a dedicated subgroup output for it will suffice. The only drawback is now that you either have to use mute groups to mute unused vox.. or have to pull unused vox inputs down.
Anyway, I have done smaller auditoriums for this.. and you would be surprised how much better a smaller, overly live room can benefit from such an implementation.
Regards,
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Mike Butler,
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Dascott Technologies, LLC

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