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Musical frequencies

  1. Aug 28, 2011 #1
    My book reads

    step 1 = 2 cos(654πt)cos(-130πt)
    step 2 = 2 cos(2 * 327 * π * t)cos(130πt)
    step 3 = f2 - f1 = 392 - 262 = 130 Hz

    t = seconds
    π = pi

    I don't see how they get from step 1 to step 2, nor do I understand how they get from step 2 to step 3.
     
  2. jcsd
  3. Aug 28, 2011 #2

    uart

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    Science Advisor

    654 = 2*327, and cos() is an even function.
     
  4. Aug 28, 2011 #3
    ok, where did the numbers 392 and 262 come from? What happened to pi?
     
  5. Aug 28, 2011 #4

    uart

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    Science Advisor

    Frequency (in Hz) is equal to the radian frequency divided by 2 pi.

    cos(a-b) + cos(a+b) = 2 cos(a) cos(b)

    You are given the "a" and the "b" and you need to find the corresponding "a+b" and "a-b" of the decomposed (into individual cosine wave) signal.
     
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