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varispeed in terms of pitch

Discussion in 'Recording' started by k2600, Sep 10, 2006.

  1. k2600

    k2600 Guest

    Hello forum.

    I have a question regarding varispeed. Hope you can help me.

    If a tape machine is running at 50 cycles and then I tweak the varispeed knob all the way down to 42 cycles, how much would this affect a sound in terms of pitch (semitones or cents).

    The reason I'm asking is because I'd like to recreate that same effect using a pitch shifting plugin... but I don't know how to set it up properly. Is there any sort of formula in order to determine the cycles to cents conversion?

    Thank you.
  2. Boswell

    Boswell Distinguished Moderator Resource Member

    Apr 19, 2006
    Home Page:
    A cent is one hundredth of a semitone. A semitone (in equal temperament) is a fequency ratio equal to the twelfth root of two (1.059463), or a difference of roughly 6%. Cents can't really be used to express pitch differences of more than half a semitone up or down (+/-50cents), because you are then nearer to the next named semitone.

    Now take your example of adjusting the speed of a tape machine. If you recorded an A (440Hz) at the 50 cps speed and then wound the machine down to 42 cps, the 440Hz would now be at 369.6Hz, which is about an F#, i.e. 3 semitones lower. You could arrive at this by ratioing the frequencies (440 x 42 / 50) and then looking up the result in a pitch table. So your speed adjustment in that direction shifts everything down by 3 semitones, and stretches the time by about 19%.

    A useful pitch to frequency table is to be found at http://peabody.sapp.org/class/350.868/lab/notehz/
  3. k2600

    k2600 Guest

    Thank you very much Boswell. That's the answer I was looking for.

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