Audio Matrix – Don’t Leave Home (or Mix) Without It

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With Audio Matrices built into consoles, you don’t have to worry about leaving them on the truck or in the shop, but you may not know why you should be using them and the problems the matrix will solve or prevent. If you are not using a matrix you probably should be and we are going to look at the reasons why you should be using the matrix, even if you don’t have complicated routing needs. Even simple setups can benefit from the extra processing matrices afford in digital consoles, if not the routing flexibility. This article is going to cover the concepts and some uses for the Matrix, and further articles will cover the “how-to” setup for the specific use cases.

How does a matrix work?

A matrix is a type of bus but has certain limitations that the other buses on the mixer do not have. Understanding these differences unlocks the matrix to help solve problems and possibly free up other mixbuses, or even save time creating alternative mixes. On analog mixers, the matrix section was mostly a way to create alternate mixes for different feeds or speaker zones. Digital mixer’s matrices provide options that would not be practical in the analog world because of all of the built in processing available on the matrix.

The limitations of the matrix are that they must be fed from another bus (a Matrix can’t be directly fed from individual channels) and they may have more limited processing available.

Since that is out of the way let’s look at different reasons you would use a Matrix:

  • A crossover to feed a PA
  • Multi-zone speaker setup – delays, front fills, outfills, subs, lobby/backstage
  • Recording/Broadcast/Press Feed
  • Extra Processing for Buses (On the X32 you can gain a 2nd bus insert using the matrix)

Matrices have to be fed by buses, but that can be as simple as the Main Left/Right bus feeding one or more matrices or as complicated as many different subgroups feeding different mixes to different matrices. This is why it may take some planning or extra time to setup groups along with matrix sends, but the flexibility they can provide is worth it.

Lets take a more in depth look at theses different setups and the flexibility they afford.

Matrix as Crossover

Even the most basic PA system stands to benefit from a system processor, but anything beyond the most basic full-range system requires a system processor/crossover. The crossover splits the signal into the frequency bands of the corresponding amplifiers. The system processor can also provide limiting and delay to further tune the system. If you do not have a system processor or you don’t have access to the venue’s you may want to built your own in the mixer so you can control it as needed.

The simplest crossover setup would be the Main L/R buss feeding:

  • A stereo matrix with high-pass filter sending output to the tops of the PA
  • A mono matrix with low-pass filter sending output to a sub or subs.

In this example you would have the ability to make adjustments to the crossover frequencies from the mixer if needed during the show by adjusting the highpass and lowpass filters on their respective matrix.

Matrix for multi-zone speakers setup

Another common use for a mixer’s matrix section is feeding different speaker zones. This could include front fills, delay speakers or outfills, a lobby or backstage/greenroom feed and the matrix gives you a way to control those mixes and process them individually from the mixer itself.

The simplest multi-zone speaker setup would include a Master Left/Right buss feeding one stereo mix out to different matrix sends. This gives you control over the volume, eq, dynamics, and timing of the different zones without having to worry about additional mixes.

On a mixer with 6 matrices like the X32, you could feed your PA left and right, mono front fills, two different mono delay zones, and a matrix sub feed without needing to setup additional mixes. You can adjust the eq (or set crossover points) on the matrix itself so you can easily make adjustment to the different zones without affecting the others.

Matrix for Recording/Broadcast/Press Feed

The matrix is a great solution for sending your mix out to a recording, broadcast, or press feed. The simplest setup is to setup a matrix for you recording or broadcast feed and send your Main L/R buss to that matrix. This is better than duplicated the Main L/R output to another set of outputs because you have separate eq, dynamics, and volume faders to further adjust the mix.

The next step up from this setup is having your PA feed from the matrix as well as your recording feed. This gives you the ability to apply eq or dynamics to both the recording feed and PA feed without affecting the other. The most obvious reason for this is that adjustments you make to the PA eq should be correcting the PA system and you wouldn’t want that to affect your recording feed. If you make these adjustments on your Main L/R buss, they will also affect the recording feed.

Custom Matrix Mixes using Subgroups

To get the most from your Matrix mixes, you would use subgroups to build custom mixes. Remember that the matrix can’t be feed from individual channels, only busses. If you have the busses or subgroups available (on many digital consoles like the X32 they are interchangeable) you can further customize your matrix mixes. A simple example would be to have a stereo subgroup for your band and another stereo subgroup for your vocals. That gives you the ability to set different levels of the two groups going to the matrix as well as the ability to apply processing to the group. You could develop much more complex matrix mixes by further subdividing your mix, with a drum group, guitar group, or whatever. This can be helpful because stage volume of guitars and drums can often be so high that in smaller venues you end up with much less of the guitar and drums in the house mix than you would want if you were sending a feed to a recording device or lobby. Having the drums and guitar on a separate group would allow you to mix more of those groups into your matrix mix than your PA.

Matrix For Additional Buss Processing

On some mixers like the X32, you may only have one insert point on each channel and buss. By using the matrix, you can gain a second insert point. One example is if you want to use a buss compressor insert like the Fairchild emulation and a Pultec EQ. You could insert the Fairchild on the Main L/R buss insert and then send that buss to a stereo matrix where you have the Pultec EQ inserted. The matrix could then feed the PA system and you would be able to use both inserts on your PA mix.

A Few Things to Remember When Building More Complex Matrix Mixes

Latency: Some consoles have latency when sending to groups. If this is the case you would just want to be sure that all of your time critical inputs are sent to a group of some kind and then from that group to the Main L/R buss or matrices.

Group Sends: Subgroups can be helpful for processing groups of channels, but you don’t need to route them to the Main L/R buss. You can setup groups and use them to feed only the matrix, giving you the option of processing them differently with more compression or different eq than you would in the PA or even send channels to the matrix that are not routed to the PA at all like a talkback to make backstage announcements via a mono buss.

Setup: Even if you are not anticipating needing the matrix, having it setup to feed your PA gives you the flexibility to add other matrix sends as necessary without affecting your PA. Then you are already setup to accommodate a range of needs that may come up. Being able to easily setup a feed for a recorder or video without having to build a mix from the ground up can save you a lot of time that you may not have.

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