Re: Fourier transform and oscillation amplitude


Randy Poe je napisal:
Pygmalion wrote:
If "mm" means "millimeters", that sounds like a strange unit
for a Fourier transform.

Why? I am doing a FT of a real signal.

You are looking at a signal with some bandwidth. You
could estimate the total energy in that signal by adding
up the energy at each discrete frequency point in the
signal (energy is magnitude squared of the FT). This
would be the same as the total energy of your original
signal.

However, since you have a signal with bandwidth, the
relationship between amplitude and energy is not
so simple, without additional information. Is it a
constant amplitude signal for instance? Is this just
a pure sine wave that got spread because the time window
was not an integral number of periods?

Well it is almost sinusoidal signal. But because it is not perfect,
frequency range has dispersed from one value to many values. Window is
an integral number of periods, I use DFT instead of FFT in order to
ensure that.

Also, if 40 mm represents a peak, what is a correct name the whole
structure?

I've heard "peak". "There is a broad peak at 50 kHz, and a very
sharp peak at 35 kHz..." I don't know if there's any formal word
in common usage.

Thanks for the answer, Marko.

.

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