Scott's PA System Tutorial: Running Sound

Page 3

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Signal Adjustment and EQing

Finally!!!! You've gotten everything plugged up and tested, and it's all working exactly the way it's supposed to . . . Right?? Good. Now, we're finally in the home stretch and we can actually get down to the fun part of running sound. The following sections concern topics that are often misunderstood, sometimes misapplied, and many times simply ignored by rookie soundguys. If there ever was a time to pay close attention, it would be now. A thorough knowledge of the next few topics is what sets the great soundmen apart from the. . . well. . . lets just call them the not-so-great soundmen. I suppose we could call them "crappy", but that would be mean, wouldn't it?.

Signal adjustment

This section will deal with the relationship between the Gain (or Trim) knob and Level slider on each input channel and the master level slider or sliders (Main) on the soundboard. At the basic level, this will be done essentially the same for both a stereo PA and a mono PA. To get the incoming and outgoing signals adjusted correctly, follow the steps outlined below.

1) Begin by setting all the knobs in each channel of the soundboard to neutral positions. To do this, turn all the knobs to the position indicated by the picture to the right. Also make sure the main sliders or knobs are turned all the way down.
2) Now, make sure all your amps are turned up all the way using the knob (or knobs) either on the front or the back of the amplifier.
3) Make sure the EQ is not in bypass mode, adjust it's gain slider (or sliders) to around 3/4, and set its frequency sliders "flat" (in other words, slide them all up to exactly halfway).
4) Now slide the main knob or slider (or sliders if it is a stereo setup) up to where you will want it set when you are actually playing. Usually a good position for this is around 3/4 of the way up.
5) On the input channel where the lead vocalist's mic it assigned, slide the "level" slider up to where you want it to be positioned during the actual performance (I usually put it about halfway up). Although using the lead vocal mic isn't a necessity, I prefer to use it for all my initial setup and tests. This is because, since it is the one that will be used the most, I like to make sure it gets the most attention as I am setting up. This way I can insure that it will be the best sounding thing in the system. You can actually use any microphone channel you have hooked up for the initial setup and testing.

Before we proceed to the next step. . .

We need to look at output level indicators. In step 6, you will have to pay attention to both the sounds you hear coming from the PA and the output indicator lights or needle gauges in your mixer. Almost all boards have different ways of metering signals so it isn't possible to describe things universally, but whether they meter things with multi- colored LED lights or needle gauges, or they simply have an overload light, they all have one purpose. That purpose it to insure that the soundboard isn't being driven too hard. The meters are there so that you can adjust the strength of the output signal to it's optimum level. Generally, too high a level will cause distortion, and too low a level will cause hiss and noise in the system, but this can vary some depending on your individual equipment.

The LED lights will usually work something like this. The bottom light will light up when a weak signal is sent through the board at low volumes, and as the volume (intensity of the output signal) increases, the next light above it will light up, and as it increases even more, the next one above it will light up, and so on, and so on. Sometimes they work left to right instead of bottom to top. These lights are usually either green or orange or yellow or red. On my soundboard, the red lights are near the top and are indicators that I am at maximum allowable output signal. Basically, that means I can't turn things up any louder than that and still expect optimum performance from my system. For your board, you should check the owners manual for specifics on where your indicator lights should be for optimum performance. If you bought the board used, and you don't have a manual, look for notation on the board itself. Even if nothing is written in words, there should be something on the gauge to indicate the best level. It may be a darker bolder marker line at the right level or it may simply be that the color of the lights is different. Usually, the lowest dark red light indicates where the signal level should be set. Ideally (at maximum volume), you want this light (or the light located at whatever level the manual suggests) to flicker on and off only during very high volume spikes. If you have the output level set so that during a performance the signal spikes a little below that light most of the time and the light is flickering only occasionally, then things are set just right. Once you have it set, you can back off on the volume if necessary. This will cause the signal lights to peak a little lower, but now you will be aware just how high your volume can go.

Typical mixer channel controls

A needle gauge meter (VU meter) works in basically the same way as the LED meter does. It will swing only slightly when presented with a weak output signal, but as the signal increases, it will point farther and farther to the right. The area where the needle is pointing is usually marked with numbers and/or multicolored regions. This works exactly like the LED meter. Usually, there will be an area marked to the right side of the gauge that is colored red. This it similar to the red lights on the LED gauge. For ideal performance, you want the needle to occasionally swing into the red area only during high volume spikes. If the needle usually spikes a little to the left of the red, and only bounces into the red once in a while, then the output level is set correctly. Some gauges might not use a color code but will instead have numbers. To know where the best level for these is, you will need to check your owner's manual. Once you have it set, you can back off on the volume if necessary.

Some boards will also include an overload or "clip" light. When this light is on, it means that the internal electronics of the soundboard are having to electronically reduce the outgoing signal. This is a safety feature that is supposed to keep the signal under control even when you aren't. Setting the signal on this kind of board is simple. If the clip light is flickering, turn the levels down just a hair until it stops. This will derermine your maximum signal level on the board. You want to avoid clipping whenever and wherever you can. Constant clipping anywhere in the system can cause damage to your speakers.

Now. . . back to step 6

6) Now, while checking (literally saying "check" over and over) the lead mic, gradually turn the gain (or trim) knob up until you begin to hear the vocal coming out of the main speakers. Don't forget to keep an eye on the output meter. Continue turning the gain up until the sound reaches the approximate volume level you will be wanting to use during the performance, or until the output meter reaches the maximum allowable output level as described above. If you reach the desired volume without exceeding the allowable output level as indicated by the LED or VU meter, then proceed to step 7. If the allowable output as indicated by the meter is reached first, you have 3 choices; 1) Keep the output signal in allowable range and run your system a little quieter than you prefer, 2) Go buy some more powerful amps and speakers, or 3) Crank it up anyway regardless of the gauges and risk destroying your system. I heartily recommend going with numbers 1 or 2. Option number three can get really expensive.
7) Once this is completed, repeat steps 5 and 6 for each vocal microphone channel. If all your vocal mics are the same model, the gain knobs and level sliders should all end up in very similar positions for each different channel. If they are not, your level sliders should all be in the same positions, but the gains (trims) may end up in different ones. Once the gains are set, you won't need to touch them again for the remainder of the gig, but the sliders will probably need further adjusting later. From this point on, the sliders will be what you adjust if you need to turn something up or down in the front of house (FOH) or main mix.
8) Now, repeat steps 5 and 6 for the other microphones (horn mics, mics on guitar amps, drum mics, and basically any instrument you have miced) except instead of checking the mic verbally, check it with the instrument that it is micing.. You will notice a drastic difference in some of the gain settings for the instruments as compared to the vocals. This is normal. You would expect a kick drum, for instance, to put a lot more volume into a microphone than a simple woohoo from the singer. One more thing to note is that active microphones will put off a much stronger signal than passive mics. The gains on active mics will probably have to be turned much lower in order to keep the level slider in its desired starting position.
9) Now, repeat steps 5 and 6 again for any direct inputs you have into your board. Those often include bass guitars and keyboards. Again, do these checks by playing the instrument (or having someone else play it) while you adjust the knobs appropriately. If none of the direct inputs is from an acoustic instrument (like a guitar or, heaven forbid, a banjo), then this step can be put off until after the system has been EQed. Keyboards don't and basses don't tend to feedback much in the PA, so they don't really need to be included in the upcoming EQing procedure.
10) Take a deep breath and proceed to "EQing".

Notes on signal adjustment

With the exception the use of the gain knob, adjusting the monitor levels will be essentially the same. However, I prefer not to adjust the monitors until I am completely finished EQing and adjusting the mains. Later, when the time comes to adjust the levels in the monitors, it should be done by only the use of the master level monitor slider (or knob) and the individual monitor level knobs on each channel. Don't use the gain. Just put the master monitor knob or slider to 3/4 of the way up and adjust the individual monitor knobs on each channel to the volume level you want. Some boards also have meters for the monitors, and the same rules apply to them that apply to the mains. Remember not to use the gain knob when adjusting the monitors. Although adjusting the gain knob will effect the monitor signal, doing so will undo everything you just did to the mains.

In a nutshell, here is how all these knobs are related to one another. This won't be a deep electronic technical explanation ( I don't have one of those), but it will at least show what each does.

----The gain knob adjusts the signal (whatever it is) as it comes into the board. It's purpose is to control or level out (or match) all the incoming signals so that they are nearly the same when they get to the other controls. This is done by either turning it up to boost the incoming signal a little or by turning it down to reduce the signal a little. Turning the gain knob up or down on a channel effects everything in that channel whether it is mains or monitors.
----The level slider on each channel adjusts the level of the signal as it leaves that particular channel on its way to the main slider.
----The main slider adjusts the entire level of all the signals as they leave the soundboard on their way to the main speakers.

Adjusting any or the above knobs will effect the levels shown on the main output level meter. It's a delicate balance that should be watched throughout the gig. Gradually turning all the levels up during a gig can result in too much output power and the clipping that goes with it. Be careful. Watch those meters and adjust the level and main level sliders accordingly.

----The monitor knob on each channel adjusts the level of the signal as it leaves that particular channel on its way to the master monitor slider or knob.
----The master monitor slider adjusts the entire level of all the signals as they leave the soundboard on their way to the monitor speakers.

Adjusting either of these (or the gain) will effect the levels shown on the monitor output level meter. Again, watch those meters when making any changes to the mix and adjust the monitor knobs and master monitor level slider (or knob) accordingly.

Now that your signals are all adjusted properly, click on "Next Page" to continue on to the EQ section.

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