Say you have a linear chirp, which is a bit like a sinusoid with a gradually increasing period, but instead of the linearly increasing period, could you pick an arbitrary value, like the red line in the image below?

a linear chirp, its period, and the period it should have (in red)

How would you write the definition of this? Say that the period variable is called AP (arbitrary period).

For the linear chirp I refer to wikipedia.

  • 5
    $\begingroup$ This is frequency modulation, see FM. $\endgroup$ – Deve Jul 29 '14 at 16:15

If I understand correctly, you are trying to create a chirp an arbitrary instantaneous frequency, $f(t)$.
In that case, the phase of the chirp is given by $\varphi(t) = 2 \pi \int f(t)dt$ and your signal in time domain is given by $s(t) = \sin(\varphi(t))$.
For example, in case of a linear chirp you mentioned, $f(t) = f_0 + \beta t$ (where $\beta$ is the sweep rate) and therefore $s(t) = \sin \left(2 \pi (f_0 t+\frac{1}{2}\beta t^2) \right)$.

  • $\begingroup$ You're missing a factor of $2\pi$ in your relation between frequency and phase. $\endgroup$ – Jazzmaniac Jul 30 '14 at 12:00
  • $\begingroup$ so, Jazz, why not edit it? $\endgroup$ – robert bristow-johnson Jul 30 '14 at 13:21
  • $\begingroup$ Could you maybe give a numerical example please? Using the red line in the image as general idea? $\endgroup$ – MisterH Jul 30 '14 at 19:00

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