EQ stands for Equalization. EQ controls are used to adjust the tonal characteristics of the signal after it arrives in the mixer from the source. These controls generally are going to effect the tone that will go to your main mixer, but not the tone that you are exporting to any Aux channels. Typically, the monitor mix would have it’s own dedicated EQ in-line just before amplification. Anyone who has adjusted the “treble” and “bass” settings on their car stereo has some experience with EQ’s, though equalization on a mixer is going to be more precise than what you have in your car.
Whenever we talk about equalization or an “equalizer”, we talk about the number of “bands” of equalization. Any mixer worth it’s salt has at least 2 bands of EQ, most have 3 and some have 4 or 5. That means that the audio spectrum is split up into X number of bands. In your car stereo, you had two bands of EQ … High and Low (or Treble and Bass). If you have 3 bands of EQ, you have High, Mid and Low. You get the idea.
Some boards (like the one at the left) have a “parametric” or shelving EQ. This means that you can change the frequency that the equalization is centered on. In the example at the left, there is a high and low band of Equalization. Each of these bands may be either “Boosted” (by turing the pot to the right of center) or “Reduced” (by turing the pot to the left of center). There is also a Mid band EQ which is parametric. The top pot works just like the high and low band pots, but the control below the mid level pot is used to adjust the frequency. This allows the operator to control a high mid to a low mid characteristic.
On the channel strip to the left, there is also a button on the low band EQ called the “Low Cut”. This is short for “Low Cut Filter” . In some cases, this is also called a “Low Pass filter” (There are also High Cut or High Pass filters, which do the same thing on the high end of the frequency spectrum). Evoking this filter will remove frequencies below a certian level. In the case at left, it says 75hz. This would be used to remove “rumble” from certian inputs.
Up to this point, I have been talking about the controls of EQ. However, the philosophy of EQ should also be considered. EQ should never be adjusted without careful listening. Additionally, you, as a “sound engineer”, should also have a “plan” for your EQ.
Each instrument and the vocals (as a group) need to have a “place” in the frequency mix. The musicians in the band have the first responsibility to make this happen (i.e., you don’t want all of the instruments playing in the same octave … we want them spread across the audio spectrum). But the sound person has the responsibility to continue that philosphy in the mix. A lead guitar should be a little louder in the upper frequencies, while the vocals will typically be in the middle and, of course, the bass in the low end.
If all instruments and vocals are given the same “place” in the audio spectrum, the mix will seem mushy and it will be more difficult to hear the individual parts. A good mix with a well designed EQ scheme from a sound person with a good ear will almost seem to come alive.
I personally believe that this is probably where Raymond (above) made his big mistake. A sound guy that cannot utilize EQ settings properly may as well be turning up the “suck” knob.
Go to Lesson 5: Channel Levels