Why is the output of power spectrum this shape?

I have a signal with 390,000 points sampled at 1kHz, called sig. Then I use the pspectrum command:

output = pspectrum(sig, 1000, 'spectrogram','TimeResolution',1);
size(output)

the size of the output is 1024x1609. How is the number 1024 computed? Since the Tres is one second and I have 390sec of data, shouldn't the first dimension be 390?

Answer 1

[the cyclist]

I expect that the answer to your question is embedded in the Spectrum Computation section of the documentation for pspectrum.