storing spectrum in real time

[romesh]

Hi all,
I am trying to log the spectrum of four signals while I am recording
the time series data also. Currently I have some sample programs to
log the time series. But I do not know how to extract the spectrum
in
real time and store it simultaneously. How can I do it?

[johnsold]

It depends upon what you mean by "real time."  That is a term which means different things to different people.

Spectral analysis typically operates by calculating the FFT of a block of data and perhaps doing some additional calculations on the results.  So at minimum your spectral analysis will be delayed by the time it takes to acquire a block of data samples plus the calculation time.  The frequency resolution is dependent on the number of samples.

This means that you have several trade-offs to consider.  How often do you save the raw (time series) data? How large are the input blocks to the spectral analysis? What else is your program doing at the same time? What it the penalty for delaying the logging of the spectral analysis?

Lynn