How does EQ work

[Lunahorum]

When an EQ plugin or effect is used, what is happening when it boosts or cuts frequencies. I know that it somehow makes certain freqs louder and softer but I want to know how it does it. I also want to know how the visual sound spectrum works that gives a visual interpretation of the different frequencies being used and their amplitudes. I think it boosts/cuts by ajusting phase but I am not sure and that still doesn't explain the sound spectrum thing.

thanks - sorry if answer is obvious this is really plaguing me and I am tired of researching everywhere trying to find the math or explanation of an EQ.

[SnappleMan]

Why do you care? I mean, every company that programs EQ VST plugins probably has their own algorithms and schematics. But, if it's anything like analogue EQs, it's a simple matter of adding or subtracting voltage.

[Lunahorum]

could you enlighten me a bit on the analogue voltage eqing? I can not find the right google keywords I am really tired.

The knobs on the guitar for tone are analogue EQs I am 100% assuming? And on those, is 5 the flatline or is 10 the flatline? I can't tell by listening as they are not as db drastic as a VST EQ which is easy to tell. Thankyou very much

[SnappleMan]

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[Lunahorum]

darn. I was hoping I could get some insight on how the voltage eq worked.

[Yoozer]

Read this part about the filters: http://braincleaner.net/?q=articles/synthesis

Then, read this: http://braincleaner.net/?q=node/9 about equalizers.

An equalizer is nothing but a bunch of band-pass/band-reject filters that have a fixed cutoff frequency (unless they're "sweepable" - then you can move the cutoff frequency around). If the frequency spectrum is the horizontal orange line you see in the pictures, then an equalizer causes this line to dip or rise at certain places. You do this to cut and boost; to shape the "local" volume of an instrument in such a way that it does not clash with another instrument that's in the same range, because if you'd overlap those two, you'd get some kind of peak, and you don't want that (well, not too much).

How a filter works is material for Electronics 101.

The knobs on the guitar for tone are analogue EQs I am 100% assuming?

Yeah, but that's because those are (in that case) the cheapest solutions (and they don't require batteries to operate).

And on those, is 5 the flatline or is 10 the flatline?

That depends; cutting and boosting is not that different. If you have an EQ and boost everything - well, that should be theoretically the same as just cranking the volume up. If you just boost the high frequencies, it's the same as just cutting the low ones and again cranking the volume up.

I can't tell by listening as they are not as db drastic as a VST EQ which is easy to tell. Thankyou very much

See if the manufacturer has specifications for this. But really, for guitars it doesn't matter that much because you're not dealing with a hyper-complex equalizer with 8 sweepable bands and adjustable Qs (the "sharpness" of the peaks or dips). Approaching this the analytical way is something you should leave to the guy behind the mixing desk, because his EQ is generally a dozen times more accurate than whatever's on the guitar.

The EQ of a guitar just has as an advantage that it kicks in before the sound goes into a stompbox; you can leave that to an engineer, too, but it's a matter of who does what and control over your tone (everyone's got a "sweet spot" in the guitar tone that they prefer.)

[Lunahorum]

I also read something about left / right panning, up / down eqing, and fader leveling front/back. What is a fader level?

[Yoozer]

Panning: controlling the volume per speaker to give the listener the idea that the instrument's coming from the left or the right.

Up/down EQ: I guess that's just a term for boosting and cutting, respectively.

Fader level: uh, that's the position of that slider (fader) which is equal to the overall volume.

but really, some context would help (e.g where have you read this).

[Lunahorum]

I read it on this site giving a 3-d analogy to mixing. Fading front and back, EQ up and down, and panning left and right

[Lunahorum]

That depends; cutting and boosting is not that different. If you have an EQ and boost everything - well, that should be theoretically the same as just cranking the volume up. If you just boost the high frequencies, it's the same as just cutting the low ones and again cranking the volume up.

That doesn't make sense to me and here is why. I am posting a picture.

[Yoozer]

That doesn't make sense to me and here is why. I am posting a picture.

Let me first tell you why it does make sense.

You've got a garden. Specifically, your part of the garden is 5 x 5 yards. Right now it's just barren earth, and it's perfectly flat.

You want to have a little hill in the middle of the garden - 1 by 1 yard, 1 foot high. Straight edges.

You have now two choices: you either add one foot of earth at that place, creating the little hill. Or - it's more work - you dig away all the earth surrounding the flat plot of land, to a depth of 1 foot.

So, what has happened now? In both cases you end up with a little hill; it's only the ground level that is 1 foot lower in the latter case.

Different example: you start with the flat garden again (the hill wasn't much of a success), and you want to create a hole of 3 x 3 yards, 2 foot deep, for a pond.

You have again the choice: either you dig away the 2 feet in the middle, or you move the ground level 2 feet up and leave the 3 x 3 yard patch in the middle on the same level.

Again, it didn't matter: the result was a hole, it's just the ground level that moved.

With EQ it's the same. The volume is the ground level (and by increasing the overall volume you move the EQ line up). Each band of the EQ means you're either creating a hill (boost) or a hole (cut).

Your example specifically uses 2 bands, but once you make 2 bumps with 2 bands, it's the same as creating 3 holes with 3 bands and increasing the volume. That your guitar doesn't have these 3 "holes" has little to do with the concept of the equalizer.

In fact, you can't even be sure that the knobs are bandpass filters - if they're lowpass and highpass, then the hole story still holds up .

[Lunahorum]

I understand completely but that only works assuming that the two humps when inverted form another hump which to my understanding they don't. They form a sharp lip. Correct me if I am wrong

[Yoozer]

Your understanding is correct. 3 peaks = 2 holes, 2 peaks = 3 holes, but given only the possibility to make 2 peaks or 2 holes, you'll end up with something volume can't transform.

But, again; if your guitar doesn't use the peaks but uses a highpass and lowpass (which is a simpler circuit), then 1 peak = 1 hole.