Re: minimum cycles for fft, and limits of filling short sample out with zeros

Rune Allnor wrote:

glen herrmannsfeldt wrote: 

(snip)

Now consider sodium at higher temperature and pressure.
The lines are broadened due to doppler shift and collisions,
and there is also reabsorption by other atoms. 

Now I am confused. Are you capable of studying each line in
its own right? Or do you just see a fuzzy wnergy distribution
with respect to frequency?


Well, the question had to do with being able to measure
frequency exactly when there is no noise.  I was trying to
find real world examples that, even without noise, one would
not be able to measure exactly.  You can study each line in
its own right if you can build a filter to separate them.
That filter is then part of the system.  It can be considered
noiseless, but otherwise should have properties that real
filters have.

If you are not able to study single absorption/emission lines,
then I would say you are dealing with a power spectrum density
estimation problem.


So, in the noiseless case can you do an exact power
spectral density measurement?

If you can see single lines and want to find their frequency
as exact as possible, then you are dealing with a frequency
estimation problem.


The claim was exact.  I am looking for reasons why it
won't be exact.

If you want to see if one line has split in two when you
modify the material, you are dealing with a line resolution
problem.


Well, sodium already has two lines without any modifying.

-- glen

.

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