"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.