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Re: sine wave equations

Subject: Re: sine wave equations
Date: Wed, 06 Dec 2006 13:54:11 +0000

I would just like to thank everyone that posted upon this issue. Especially re: spatial aliasing as this is the problem I think. I hadn't heard of it before and some of the help emails were a bit cryptic to me until I did some background reading (wikipedia). But I get it now and I think that is THE problem. So, thanks so so much to everyone that toook the time to read, think or reply in regard to my problem. Kind regards,

From: Miroslaw Kwasniak <address@hidden>
To: address@hidden
Subject: Re: sine wave equations
Date: Sun, 3 Dec 2006 14:52:26 +0100
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On Sat, Dec 02, 2006 at 12:45:02PM -0800, Paul Roberts wrote:
> Most likely just an aliasing problem.

I'm sure that it is.

> Make sure that you have a high
> enough sampling frequency in x. For example, lets say that x
> represents space. The spatial frequency of your sine wave seems to be
> 1/lambda. To sample the function properly, your delta_x should be at
> least as small as lambda/2. So you would use:
> delta_x = lambda/2;
> x = x_min:delta_x:x_max;

Don't forget that the sampling theorem (known as Nyquist or Shannon theorem,
I suppose that most official name is now: Whittaker-Kotelnikov-Shannon
theorem) is about an uniform-sampled representation of time-continous
signal, which can be perfectly (and uniquely) reconstructed from samples.

If don't like playing with a signal reconstruction/interpolation but only
want to use samples to make a plot I always say - use at least 10 samples
for signal period (that is 5 points for a half sine) to get a sensible figure.

> If you wanted to oversample, you could use a smaller delta_x
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