MATLAB: How to specify the FFT length for the spectrum objects in the Signal Processing Toolbox 6.2 (R14)

dspoptsfftlengthnfftobjectpsdpsdoptsSignal Processing Toolboxspectrum

I am using the spectrum.welch objects, and the documentation is not clear on how to specify the FFT length. There is some mention for using "User-Defined" and the dspopts object, but there are not any examples.

Best Answer

This bug has been fixed in Release 14 Service Pack 2 (R14SP2). For previous releases, please read below for any possible workarounds:
The documentation on setting the FFT length for the Spectrum objects is missing from the Signal Processing Toolbox manual.
To work around this issue, use the following code as an example for changing the FFT length for the Spectrum objects:
% Sample test data to perform the Welch method on:
t=0:0.001:2*pi;
x=sin(t);
% Initialize the Spectrum and Options objects
Hs=spectrum.welch;
Hopts=dspopts.spectrum;
% Change the options to use user-defined FFT length and Sampling Frequency
set(Hs,'FFTLength','UserDefined');
set(Hopts,'NFFT',512);
set(Hopts,'Fs',1000);
% Display the results
psd(Hs,x,Hopts)
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