Hmmmmmm....Not to be a smart ass (okay, I DO mean to be a smart ass.....) but the original statement more or less was "I know what an EQ does" then followed by "But what do they mean....." and asking the question of EXACTLY WHAT AN EQ DOES!!!!
The moral being, you DON'T in fact know what the hell an eq does, otherwise it would make perfectly good sense what these people mean by "cutting this, and boosting that...."!
The truth is liberating isn't it! You DON'T know nothing about EQ, so now you get to learn from the MASTER of it!!!
Chris Shaeffer's post more or less covers it pretty well. (funny how us Portland guys dig right in on this EQ stuff eh?
) I will EDUCATE you on a bit further, since you don't know nothing about it....
Equalization obviously means to make something "equal". In audio, this is used to balance "frequencies". Frequencies is the same as "cycles", which is how many times per second something vibrates. Sound is vibrations (obviously), and the "pitch" (frequency (cycle)) is how many times per second that sound vibrates per second. Sorry for the elementary education here, but then again, you DON'T know squat about EQ, so I must assume you need this....
So, the fundamental note of any instrument vibrates a certain amount of times per second. It should be noted though that just about every instrument sound you hear is not JUST the fundamental note, but rather, a collection of frequencies combined. The combining of these frequencies follows a somewhat predictable "stacking" of the notes that is known as the Overtone Scale. Look that one up! It is fun. So, instruments get their individual sound from different emphasis of the notes that are above the fundamental. If all notes in music were just pure tones, you wouldn't be able to tell apart a trumpet from a gazoo (although, most trumpet players have a funny way of making their instrument SOUND like a gazoo!
). Because each instrument, when playing a given note, have a collection of notes above the fundamental, that instrument has it's own distinct sound. Cool! (and I bet you didn't know any of THAT either!!!
)
Now, how does EQ come into play here? Just be patient damnit!!! You guys that don't know nothing sure are impatient!!!!
Now, when mixing music, we may want to "balance" the sound of certain instruments to give them a bit more definition in a blend of instruments. Since instruments have a RANGE of frequencies that they create when they play, there is a pretty good chance that there will be overlap between instruments in the audible hearing range, which happens to be between 20 and 20,000 cycles per second (go back and read there unknowing one...that is 20Hz-20KHz (KHz= Kilo Hertz....Hertz=Cycles per second...the guy who discovered this was named Hertz (no he didn't start the car rental company...might have been his brother though...who knows).
So, in our range of hearing, roughly 20Hz-20KHz, many of our classic instruments have vibrations they create that fall within this range, and obviously, because two instruments playing at the same time may have the same fundamental note (but different overtones, which is what makes them sound distinct from each other!) there can be some conflict! What should we do about this? What if the overtones of one instrument are dominating the overtones of another instrument in a way that is undesireable?
Well, we can create a cicuit that "selectively filters frequencies" so that we may apply this filter over one or both instruments to perhaps either turn down or turn up a selective frequency, or even a RANGE OF FREQUENCIES (keep that in mind.....I will cover that in a bit! and grab me a cup of coffee while I explain...I AM the teacher here you know....
. This filter circuit is what is known as an EQ. It is used to "EQUALIZE" the sound many different ways. It does not neccesarily mean that it will make all frequencies the same volume. Nope, that wouldn't help. But maybe that is what is needed eh? Anyway....
There are many different designs to an Equalizer: Shelf, Low/High Cut, Bell. The different designs are used for different purposes.
Here is some eq terminology that you MUST know (hey, WAKE UP, I am teaching here....you guys who know nothing sure get distracted easily!
)
Cut: To turn down, or lower the volume.
Boost: To turn up, or raise the volume.
Frequency: Cycles per second
Que: Think of this as the RANGE of frequencies.
So, now you know some terminology. You might think you have graduated. Ha!!! School is JUST beginning youngen!
Now lets talk about the different eq's that are available.
Shelf: A shelf eq is called a "shelf" because this type of eq effects frequencies ABOVE or BELOW the frequency that is displayed for it. On your normal Mackie mixer, you have a High EQ, with a little number by it sometimes that says 12KHz (not all models have this number by the High...like this junky 1202 I just looked at...). Anyway, I KNOW that the Mackie High Shelf EQ is set at 12KHz because I READ THE FREAKIN' MANUAL!!! (like you should....) So, that eq knob will effect all frequencies ABOVE 12KHz!
The Low EQ knob on a Mackie I beleive is set at 70Hz (an odd place to set it, but then again, Mackies are odd in every way!!! Including the way they sound.....yuk!!!). So, the Bass Shelf EQ effects frequencies BELOW 70Hz.
On either knob, if you turn it to the left, you are "cutting", or "turning down" the frequencies BELOW/ABOVE the "shelf" point (the frequency that the EQ is set at). If you turn it to the right, you are "boosting", or "turning up" the frequencies BELOW/ABOVE the "shelf" point.
Easy enough. Shelf EQ's are more of less exactly just like what you have on a stereo system (like was stated so cleverly earlier by TexRoadkill). They add/subtract frequencies below/above whereever the circuit was set to effect!
Shelf EQ's effect the frequencies below/above the set point EVENLY! (remember this dood!) meaning that all the frequencies above/below the set point are turned up equally.
On shelf EQ's, you will usually see some numbers and markers around the knob, and at either end of the knobs range, you will see something like -15 and +15. This is the amount the effect frequencies are turned up/down is DECIBLES. A decible is a unit of measurement if sound pressure level. So, if someone says to cut the Low Shelf 2 dB, they mean to turn down the Low Shelf filter 2dB! Easy eh? I will not go into relativity of sound pressure level here, but a 6dB cut/boost is approximently a doubling/halving the volume of something (some argue that the ear responds to a 10dB cut/boost...and that may be so, but in measuring sound, 6dB is the standard). So, for what that is all worth!
Cut Filters:
The kinds of EQ circuits are more of less like shelf eq's except in two ways. One: They only turn frequencies DOWN! Two: They DON'T turn all the frequencies down the same amount. They turn down frequencies based upon a "Slope". Yup, meaning how it does it looks like a slope, or a hill would look. So instead of turning all the frequencies down the same amount, the frequencies farther away from the set point of the filter will be MORE effected than the frequencies closer to the set point. How it does this is measured is "dB's per octave". So, a 12dB Slope would mean that if the filter was set to 100Hz (100 cycles per second...remember student?
), 50Hz (which is an octave lower than 100Hz) would be turned down 12dB. 25Hz would be turned down 24dB...etc.....
Bell Filters:
Bell Filters are usually the "midrange" eq. To understand why "Bell" was used as it's name, you have to think of what a bell looks like. (go ahead, think about it......I will wait)
Okay (yes, I AM a smartass to people who know so much, just like you!
), now a Bell Filter effects frequencies BOTH ABOVE AND BELOW the set point of the filter. How MUCH above/below it effects frequencies is called the Que (or bandwidth). If you seen the effects of a Bell Filter displayed, it's effect on the sound would make the display look like a bell! That is why it is called a Bell Filter! Duh!!!! The center of the bell is the set point of the filter.
Now, the Que (remember? Bandwidth, or maybe just think of it as the width of the bell shape) is measured is "decible per octave", just like the Cut Filters are, BUT!!!!, frequencies CLOSEST to the set point are effected more than frequencies farther away from the set point, which is EXACTLY OPPOSIT of the Cut Filter. Ahhhhhhhhhhhhhh, so confusing eh? Well, not really, that is just the way it is...live with it.
It should be noted that bell filters ALSO have a Slope too!
So, Bell Filter set at 500Hz, with a Que of 2 octave, and a slope of 6dB per octave, that is boosted 12dB would do this:
500Hz would be boosted 12dB. 1KHz would only be boosted 6dB, and 250Hz would be boosted 6dB. Cool eh? 2KHz wouldn't be boosted at all, nor would 125Hz (before you go asking a typical newbie question as to why, graph it out!!! You ARE the smart one who knows everything about eq right?
)
So, NOW you know a LITTLE something about EQ!!!
Your mixing console could have any number of combinations of ways to EQ the sound. This junky Mackie 1202 only has a Low and High Shelf filter per channel. My Soundcraft Ghost that I used to own has a Low/High Shelf, as well as two full Parametric EQ's. I have seen consoles that have up to 7 semi parametric eq's!!! Ahhhhhhhhhhhhhhh...you thought you knew so much, yet, you are asking "What the heck is a Parametric Eq? And for that matter, what is this semi-parametric thing all about"?
Bow to your teacher first and I will continue!!!! I will wait........
Now that you knees are dirty.....
I will explain the different KINDS of controls you MIGHT have on your eq circuit.
Low/High Cut: Usually these are set to a certain frequency, and you can either turn them on or off. Sometimes, on better consoles, you can select between two different cut frequencies. There will usually be a switch or button to do so. READ YOUR FREAKIN' MANUAL to find out if you have this or not!
Low/High Shelf: Usually, these shelf eq's are set at a certain frequency, and the knob is the Gain setting (meaning how much you can turn it up or down). On nicer consoles, you can also select at what frequency the shelf filter will work at. That could be a button that selects between two frequencies, or a variable knob that covers a range. RTFMDS!!! (read the f*cking manual dumb sh*t!) to find out where yours is set at. If you have Variable selection of the set point of this circuit, you will see numbers by the knob that display frequencies...etc..... On console with Variable Frequency Selection for the Low/High Shelf Filter, you will have that control and well as a Gain control.
Bell Filter:
Bell filters come is three types:
Fixed: This is what is on many "budget" consoles. The Frequency, and Que are set. You cannot change them. You only have a Gain control.
Semi or Quasi Parametric: On this type, you can select the Center Frequency of the filter, and have a Gain control.
Full Parametric: On this type, you can select the frequency, AND THE QUE, as well as you have the Gain control.
I have yet to see any Bell Filters where you can control the Slope. Maybe in some digital eq's you can. But traditionally, the Slope is different from manufacture to manufacture, each claiming there is the best!!! In the case of Mackie, this is of course a bold lie!
as their eq's are possibly some of the most stale, godawful sounding stuff in the universe! LOL...(yup, sonusman loves to hate Mackies....).
So, here you have been educated on what eq is, what it does, and what different kinds there are, as well as what the controls do. Cool! But you STILL DON'T know SQUAT about EQ!!!
What you will find in time is that as little eq as you can possibly use is the BEST eq you can possibly use. Nope, I am not afraid to use it, I just don't like to if I don't HAVE TO! Less is more usually.
Eq can be used to correct balance problems on the recorded track, of as an "effect".
So much more could be written here about eq, but I think this is enough for now. You will be out there eqing until you are blue in the face, trying to figure out "how the pro's get THAT sound" and what not. Have fun! We "get THAT sound" at the source and mic it well, and usually use as little eq as possible while mixing! This is the god honest truth, and any decent engineer will claim the same thing, and not just because we don't want you to know out eq "secrets". The "secret" is to work towards a sound that is right in the first place, thus avoiding the use of eq later to make it "right".
Okay, class is out!
Oh, and sipi1910. QUIT SHOUTING IN HERE!!! We can hear you just fine! (this IS just a small room in the vast ocean of the internet you know....
)
Ed