A little physics problem peeps..

[Whiternoise]

Hi,

I need a good explanation of frequency spectra. e.g

http://upload.wikimedia.org/wikipedi...d_spectrum.png
and
http://upload.wikimedia.org/wikipedi...-td_and_fd.png

I just can't make sense of how you go about making a graph of the spectrum when you're given a waveform.

Someone here must have a physics degree..
Thanks much

[Stoo]

Wavelength, Frequency, Amplitude..

That's all you should need..

Or you could cheat and google "Electromagnetic Spectrum"

[Whiternoise]

Yeah, i thought that, if you're given a waveform.. which bits do you take to form the spectrum?

[Stoo]

umm... It's just a list of what the waveform is composed of?

[blueball]

One is looking at the waveform in the time domain. The other is looking at it in the frequency domain.

The function to convert from one to the other is a Fourier Transform - they are hideous! You can convert between "Fourier Pairs" (as they are called) and back again. two common Fourier pairs are time and frequency. On your first link you see the amplitude of the voice signal at each point in time in the left hand picture. The amplitude includes all the frequencies being transmitted at that time. The right hand picture shows the intensity of each frequency being transmitted. This can be at an instant in time or, as is the case here, combined over a 15 second period. You effectively get two different views of the same information.

I'm not sure I've explained it as well as you would want but basically Fourier transforms allow you to convert from time to frequency and back again.

[charleski]

The wikipedia pages are for people with a reasonable amount of maths. If you want a set of pages that explain the concepts behind the Fourier Transform you could try this.

[Whiternoise]

Ok thanks, i found this did the job: http://physics.mtsu.edu/~wmr/fourier_1.htm

[Steve B]

fourier transforms /hides

[Stoo]

You can sit and watch seti@home doing fourier transforms, it's quite pretty

[superscaper]

I had years of attempted learning of Fourier transforms and I hated it but luckily I don't need them any more but I'm sure they'll crop up again.

[Nick]

Isn't that where you change the colour of the pelt?

Oh hang on, that's Furrier Transforms... my bad.

[Steve B]

Isn't that where you change the colour of the pelt?

Oh hang on, that's Furrier Transforms... my bad.

hang your head in shame nick...