The Difference Between FFT Spectrum and Power Spectral Density

I always teach the difference between FFT Spectrum and Power Spectral Density on my DSP courses and many students find it confusing.

This applications note from Audio Precision summarizes the subject very neatly : The Difference Between FFT Spectrum and Power Spectral Density

Functions for calculating both the FFT Spectrum and Power Spectral Density are included in the SigLib DSP Library.