Equalization 101?

[beatgorilla]

Hello all,
How does the word "octave" correlate with the frequency spectrum. I see it on eq's and hear it tossed around all the time, but I really don't know what it means. Are there a fixed number of octaves between 20hz-20khz? Is it the volume of frequencies or the range? I'm clueless.

[cmchamp]

An Octave is roughly a doubleing of frequency, raise in pitch, or halfing of the wavelength.
20Hz - 40Hz is an Octave
200Hz - 400Hz is an Octave
Middle C to the C above Middle C is an Octave.
When you see "1/3rd Octave EQ" That means that the octave from 25Hz to 50Hz is broken down into three bands. Same goes for the 250Hz to 500Hz Octave and the 500Hz to 1000Hz Octave.
There are roughly 10 octaves that we can hear all or part of between 20Hz and 20,480Hz.

[bernchesters]

An octave is simply a power of 2 multiple of a fundamental frequency. One octave up is 2 times the fundamental, and one octave down is 1/2 the fundamental. For example, if the fundamental frequency is 440 Hz (A440 on many tuners), one octave up would be 880 Hz, and one octave down would be 220 Hz.

Two octaves up from 440 Hz, however, would be 1,760 Hz, since you have to double 880 Hz (one octave up), or quadruple the fundamental of 440 Hz. That's where the power of two multiple comes in. The frequency at X octaves up or down from the fundamental is (2^X) * fundamental. If you go up octaves from the fundamental, X is positive, and if you go down octaves from the fundamental, X is negative. That's why if you go down one octave you get 1/2 the fundamental frequency, since 2^(-1) = 1/2.

As far as the number of octaves for the human hearing range, there are generally considered to be 10, and each frequency band (or octave) is defined by its respective center frequency (63, 125, 250, 500, 1000, 2000, 4000, 8000, and 16,000 Hz). The center frequency is the square root of the product of the uppermost and lowermost frequencies in the band (which are an octave apart).

Sorry for all the math if you're not mathematically inclined. Being an engineer, it's hard not to describe mathematical terms without using mathematical language. :lick:

[bernchesters]

Looks like Cory got a post in before I finished mine...oops.

[cmchamp]

No problem. Two different ways of thinking about it. Unfortunately, I don't think in frequencies. I think backwards from notes. Being a trained music educator first, and the tech side of things later, I tend to find the note, then go to the frequency if that's what I'm searching for. Being well adept at both techniques really helps you get the job done as well as more easily communicate with others.
C.

[beatgorilla]

Great advice, guys!!!! So on bernchester's post he mentioned 10 octaves but there is only 9 listed in parenthesis. So I would assume that the first octave would be 31.5 or 31hz since 32khz (16,000x2) is not within the 20khz range? BTW, a friend of mines has these cds that are supposed to help you train your ears to recognize frequencies. Don't know if thats valid or not, but I wanted to give it a try.

[bernchesters]

So on bernchester's post he mentioned 10 octaves but there is only 9 listed in parenthesis. So I would assume that the first octave would be 31.5 or 31hz since 32khz (16,000x2) is not within the 20khz range?

You are correct in that the first frequency band is centered at 31 Hz. I seemed to have left that one out in my explanation. You are also correct that the next frequency band above 16 kHz would certainly be outside the range of human hearing.


Being well adept at both techniques really helps you get the job done as well as more easily communicate with others.

Very true.