MATLAB: Are frequencies that are returned by PWELCH appearing in the center or left hand edge of the energy band

Question

One output from the PWELCH function is an array of frequencies. I would like to know if these frequencies appear at the center of each energy band or the left hand edge.

Answer 1

All of the power spectral density (PSD) estimation functions in the Signal Processing Toolbox, such as PWELCH, calculate the PSD at equally spaced frequencies in the range of [0, 2*pi) for normalized angular frequency, or [0, Fs) for linear frequency.

The total average power of the PSD is approximated by the area under the PSD curve. We approximate this total power by breaking up the area under the curve into vertical rectangles, or bins, then summing them up. Since we start summing these bins at F = 0, one can define these frequencies as being left-hand justified or simply left-hand frequencies.