Have you ever wondered what the “MATRIX” on a mixing console is used for? In this session of “How to Mix Live Music”, we are going to find out! And we’ll talk about using the MONO or SUB buses too. On the TF mixer, if you look at the OUTPUT fader layer, you will see the SUB bus as well as the Stereo Master. You can guess that this is designed to be used with subwoofer speakers! You may just have one subwoofer, or you may have one positioned on each side of the stage. Anyway the send is usually mono, because low frequencies spread widely and It's more difficult to sense the direction of their source. So panning SUB frequencies is futile. By selecting the SUB, and looking at its SEND FROM window, you can see each channel has an independent level and ON switch for the SUB send. It’s only worth sending channels with low frequency content, such as kick drum, bass guitar and keyboards. But it's nice to set a balance between the channels. Then the SUB bus has its own EQ and Low Pass Filter. This would normally be set somewhere between 80 Hz and 125 Hz, depending on the specification of the subwoofer units. Finally, the SUB fader level is usually linked to the Stereo master. But if you want to change the offset, hold SEL while moving the SUB fader. Then you can boost or reduce the SUB, while keeping the link. The MGP32X has a MONO bus which can also be used to send audio to subwoofers, but in this case it is less flexible, though easier to setup. The same channels that send to the STEREO master are also going to the MONO bus, at the same fader level. So it is extra important to use a Low Pass filter with any subwoofer. Good job the MGP includes one, controlled from the LCD screen. Press SETUP once or a few times until the LPF (MONO) window appears. Then switch on the LPF and set the frequency. Use the MONO fader carefully, to avoid the low frequencies from resonating around the room too much, and overpowering the mid-range frequencies that make vocals easier to listen to. Next let’s consider the MATRIX. The MGP keeps it simple with 2 outputs and only level adjustment, while the TF provides versatility for the more advanced users, with 4 outputs all featuring EQ and delay. So what can the MATRIX be used for? Most commonly, it is used to feed sound to additional speakers in a PA system. For example, the stage might be very wide, and the main speakers far apart. So the audience members sitting in the center of the front won’t hear so clearly. So you can provide them with “front-fill” speakers, and use the MATRIX to vary the sound mix and level they hear. Another possibility is for additional small speakers to reach under a balcony, or speakers towards the back of the room to reinforce the sound to the seats at the back. They all may need a slightly different mix and level. So we can use the MATRIX: note that each Group as well as the main Stereo L and R can send to the MATRIX, so you can vary how much vocal compared to instrument can reach the additional speakers for example. The MATRIX outputs of TF mixers feature a delay. Let’s consider how to use that. Imagine that from some seats in the audience, you can hear some sound from the main PA speakers, but it's not loud enough. So you add some speakers closer to these seats. Now the people in these seats can hear the sound from two sources: the near speaker and the far speaker. But the sound from the near speaker reaches them first, because the sound signal travels through a wire much faster than it does through air. This can create an unpleasant sound for the listener, and it draws more attention to the nearby speaker than the stage. To compensate, add delay to the sound for the near speaker. The amount of delay needs to match the time it takes sound to travel from the main PA speakers to the speakers fed by the MATRIX. Don’t worry: the TF mixer will do the maths. You just need to measure the distance between the speakers in meters or feet. Enter that distance into the TF MATRIX DELAY screen, and it will calculate the time in milliseconds. Apply the delay to tidy up the sound! It should help the audience in those seats to hear clearly, but still to connect the sound with the action on the stage. Another use for the MATRIX is to send audio to a recorder, perhaps for archiving or for webcasting. Again, a variation of levels between the groups may be required to make a better mix for listening on small speakers or headphones. The USB recorder on both mixers can be set to record 2 MATRIX channels instead of the Stereo Master. Did you know, some of the largest live sound mixers have as many as 36 MATRIX outputs, for sending sounds to all sorts of different areas and locations: some theater sound systems can become very complex! Anyway, that’s all for this session. Next time, we’re are going to start using compressors, to control the dynamics of certain input channels. See you again soon.
