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
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Topic: Understanding LCR/LR+M Mixing (Read 23581 times)