"Porky" wrote in message

"Arny Krueger" wrote in message
...
"Porky" wrote in message


The experiment I suggested will give the results I gave, and if it
is right at under the circumstances I suggested, it should be right
under all circumstances with the same conditions, right? In other
words, if it applies with a LF of .1 Hz or 1 Hz, it will still apply
at LF's 20Hz or 50Hz, is that not correct?

right. However, its a lot harder to properly measure doppler when
the LF tone has a very low frequency. To measure it with a FFT you
must use a FFT size that covers at least one cycle, and hopefully
several cycles of the process. If the LF tone is 0.1 Hz, this means
an absolute minimum of 10 seconds of data, and ideally 30 or more.
At 44,100 Hz sampling, this would be a FFT composed of a minimum of
441,000 samples, and preferably several million samples.

Consider the original example - the LF tone was 50 Hz. It had an 882
sample
period. Note how much overkill there was when analyzed using a 65k
sample FFT, or as I used a one million point FFT.

One of the problems with FFT analysis that we've all overlooked is
that we aren't really dealing with analog waveforms in our
simulations, and we can get erroneous results when using high FFT
numbers because we start playing in the digital "cracks", so to
speak,

I'd like to see a believable fuirther explantion of that.

FFT and I are going on our 42nd year, and we've been pretty good friends the
whole time.

Having done a bit of experimentation, I've found that I get
the most consistent results across the whole range be using an FFT
number of 16K or 32K, higher rates give false results, especially at
higher frequency HF tones.

I'd like to see a believable further explanation of that.

Alternatively, if your equipment will
handle it, try creating the wave models at 24 or 32/96, or even
32/192, you'll see a considerable difference in your results,
especially at higher HF tones and FFT numbers, and your results will
be more consistent across the entire range of LF and HF tones.

I'd also like to see a believable further explanation of that.