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How to Become an Audio-Mixing Ninja

This article is designed to help you avoid some of the many pitfalls that you can fall into when doing audio mixing for live production.

Pot Too High/Pan Wrong

Down at the bottom of the mixer you’ll find the pan controls and potentiometers (Figure 4, below). On smaller mixers, the potentiometers (aka pots) are knobs. On the mixer shown in Figure 4, they're sliders. You can see that there's headroom over zero, and space above it is there so people feel they have the ability to cleanly make things louder.

Figure 4. Pan controls and potentiometers.

Many times, I see people who are not familiar with the hundreds of knobs found on an audio mixer--especially if it's a bigger mixer, such as a live sound mixer that has sweepable EQs and four aux sends and returns and an FX send--I see these people get down to the bottom of the mixer and the pan control is just another knob they ignore. They don't notice that someone else had adjusted the pan on the mixer and they're all panned left or panned right or adjusted in some way and then they wonder, "Why am I only getting sound out of those speakers or these speakers?"

Or perhaps they're using one mixer for both streaming and house soud. Sometimes they'll take that main mix and split it: the left-channel main mix goes to your stream, and your right-channel main mix goes to house.

Technically, you want them to be the same, but it's not going to work if somebody has adjusted the pan and it's slightly to one side. They’ll say, "Why can't I get more out of him on the web feed when he's so loud in the house?" That's because the pan is misadjusted--the master is too high or too low.

Figure 5 (below) shows a mixer that has separate left and right controls for the main mix. But if you have a smaller, budget mixer, this will likely be just one knob. You won't be able to adjust one or the other independently. That's where the pan comes into play. You have to do everything there in the pan. But even with separate Main Out sliders, you still have to pay attention to the Pan setting of every signal you're working with.

Figure 5. Some mixers have separate left and right main mix sliders; others have just one knob.

Over-Mod on Amp Input

You can actually over-mod on your amplifier input. One of the key reasons is that not all line levels are created equal. There's professional line level and there's consumer line level. They are two different output levels. Professional line level is +4dB, and consumer line level is -10. If you're using a professional mixer, on the back you’ll find a switch that allows you to adjust the output level, or make sure to adjust your main out to compensate. .

If I'm going to feed my input into a piece of consumer gear--for example, a laptop that's going to handle my web stream--I want to make sure I'm not feeding it a really hot signal, because I want it to be at zero. I want it to be nice and even.

Fortunately, some amps even have input trims. Figure 6 (below) shows a Crown amp that has internal crossover. If you just want to use this amp for your bass drivers in the house, then you can tell the amp to strip off everything above 250Hz. Most times, once amps are installed, they're in a rack somewhere and nobody touches them. Nobody can mess them up once the professional installer has set them, and this is good. But sometimes, if an amp is in a portable rack, it can get adjusted too.

Figure 6. A Crown XLS2000 amp

Feedback

How many times have you heard feedback during a presentation? We all know what feedback is: The room audio gets into the mic, which gets into the room, which gets into the mic. Figure 7 (below) what feedback looks like on a scope. This one is around 1k but there's the main feedback peak and then you can actually see that there's two overtones: one above 2k and one above 5k.

Figure 7. Feedback as shown on a scope

If you have a 30-band EQ, you can use it to correct room audio, operators will often notch the feedback without notching the overtone. Those frequencies are hanging around, ready to give you some feedback. These days, thankfully, feedback is easy enough to manage that we can use hardware to kill it. The Behringer Eurorack mixer that has appeared in several figures in this article has a feedback exterminator (Figure 8, below). All you do is you push the button and the digital circuitry puts a notch in as soon as it hears the feedback coming.

Figure 8. The Behringer Eurorack mixer has a built-in feedback detector.

I don't know how many are built into this box but generally, there's enough to handle most easy room problems. Then, of course, there's an EQ for the room as well. If you're finding that the room is a little bassy, or it's too live,you can correct for that as well.

If you don't have a mixer that does that, you can buy outboard devices, such as the Shark shown in Figure 9 (below). A lot of companies make them now. This goes in between the mixer and the amp. It takes the output of your mixer and it doesn't raise the level. It doesn't lower the level either, but it listens for the rising tone and it puts that notch in.

Figure 9. Behringer's Shark FBQ100

It's important though that these feedback exterminators need to be set. You'll find guys that go into a room before a big show, and they'll open up the mics, put them on a table, and slowly raise the house. They'll raise the audio and then you'll hear that first note come in, and then you'll hear it go away.

They'll raise the house a little more and you'll hear the second note and they'll give it a notch. Technically, you can try and keep going but as you keep going, you’ll get more and more feedback. What these devices do is let you get a few dB louder in the room than you could without them. In many rooms, it will help, but in a difficult room--say, if the room had marble on the walls--that's going to be tough, because it's just so reflective with sound. You might have to keep your overall audio level much lower.

I worked in a facility where the main hall had a glass ceiling and tile floor. It was quite reverberant. They had big speakers set up on top that shot outward. It bounced around a little bit before it came down, and without one of these, the room was basically unusable. You could never get it loud enough on the floor, especially if there was a big crowd, because there's always a percentage of the crowd not paying attention, carrying on their own conversations, chatting, phones ringing, things like that. In those situations, these things are very handy to have.

Conclusion

So the key to good audio is mastering the entire signal path from the source of the audio to each and all of your intended destinations. It's more than plugging in a mic and pushing up a slider. You need to be certain of proper audio levels all the way through the chain, and that includes several areas before and after the mixer. By mastering the entire path, you can become an audio ninja.

Watch the video below for a detailed audio mixer video tutorial to round out this article:

 

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