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Go Back  Dogs On Acid > The Grid Reload this Page > question about audio frequency log scale (maths)
 
 
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09-27-2011 10:06 AM
question about audio frequency log scale (maths)
So I'm writing a little program to generate a pitch sweepable sine wave.
It's easy enough to make it linear.
I have a seekbar with values from 20hz to 20khz, but I want to make it a log scale and I'm completely lost.


What's the equation to find the next interval (up or down) from a given frequency.

Or maybe, a better question, is how do convert and arbitrary linear scale to a log scale relevant to frequency?

My brain is now boogaloo
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09-28-2011 01:57 AM
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Originally Posted by parsley View Post
I have a seekbar with values from 20hz to 20khz, but I want to make it a log scale and I'm completely lost.

What's the equation to find the next interval (up or down) from a given frequency.

Or maybe, a better question, is how do convert and arbitrary linear scale to a log scale relevant to frequency?
The logarithm represents the exponent that 10 is raised to. That is, 100 = 10 to the power of 2, therefore log 100 = 2.

Similarly, 1000 = 10^3 so log 1000 = 3.

You would have an exponential function f(x) := 2*10^x
If you take values of x from 1 to 4 you'd get the familiar 20-20kHz sweep.
f(1) = 2*10^1 = 20 Hz
f(2) = 2*10^2 = 200 Hz
f(3) = 2*10^3 = 2 kHz
f(4) = 2*10^4 = 20 kHz

Rather than sweeping from 20 to 20 000 by a step of 1, you would sweep from 1 to 4 with a step of 0.01 (or whatever values are appropriate for the rate of change).

I hope that's of some use!
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09-28-2011 07:29 AM
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Originally Posted by DrTiTus View Post
The logarithm represents the exponent that 10 is raised to. That is, 100 = 10 to the power of 2, therefore log 100 = 2.

Similarly, 1000 = 10^3 so log 1000 = 3.

You would have an exponential function f(x) := 2*10^x
If you take values of x from 1 to 4 you'd get the familiar 20-20kHz sweep.
f(1) = 2*10^1 = 20 Hz
f(2) = 2*10^2 = 200 Hz
f(3) = 2*10^3 = 2 kHz
f(4) = 2*10^4 = 20 kHz

Rather than sweeping from 20 to 20 000 by a step of 1, you would sweep from 1 to 4 with a step of 0.01 (or whatever values are appropriate for the rate of change).

I hope that's of some use!
thats what i needed. that really helps it was very hard to find this information distilled like that. you are an absolute gent.
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