question about audio frequency log scale (maths)

Sep 27, 2011

  1. parsley

    parsley
    6,600 posts
    Since Apr 25, 2004
    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
  2. DrTiTus Finger rollin rhythm

    DrTiTus
    576 posts
    Since May 16, 2005
    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!
  3. parsley

    parsley
    6,600 posts
    Since Apr 25, 2004
    thats what i needed. :twothumbs: that really helps it was very hard to find this information distilled like that. you are an absolute gent.