Hein ten Horn wrote:

> Hmm, let's examine this.
> From the two composing oscillations you get the overall
> displacement:
> y(t) = sin(2 pi 220 t) + sin(2 pi 224 t)
> From the points of intersection of y(t) at the time-axes you
> can find the period of the function, so examine when y(t) = 0.
> sin(2 pi 220 t) + sin(2 pi 224 t) = 0
> (..)
> (Assuming you can do the math.)
> (..)
> The solutions are:
> t = k/(220+224) with k = 0, 1, 2, 3, etc.
> so the time between two successive intersections is
> Dt = 1/(220+224) s.
> With two intersections per period, the period is
> twice as large, thus
> T = 2/(220+224) s,
> hence the frequency is
> f = (220+224)/2 = 222 Hz,
> which is the arithmetic average of both composing
> frequencies.

As I said before, it might be correct to say that the average, or
effective frequency is 222 Hz. But the actual period varies from
cycle to cycle over a period of 1/(224-220).

>>the amplitude of which is easily plotted versus time using Mathematica,
>>Mathcad, Sigma Plot, and even Excel. I think you should still give that a
>>try.
>
>
> No peculiarities found.

Perhaps you would agree that a change in period of less than 2% might
be difficult to observe - especially when you're not expecting to see
it. To more easily find the 'peculiarities' I suggest that you try
using more widely spaced frequencies.

> gr, Hein

gr right back at ya,

jk