Fourier Phase Angles

[TomPaceHDR]

I was looking at the Fourier Phase output of SeismoSignal, and I have three concerns:

1) The Help System indicates that the Fourier Phase angle is computed using the ATAN function. This function can only output phase angles between -90 and +90 degrees, and the program output is within this range. However, the range should be -180 to +180. (This could be handled with negative amplitudes, but SesimoSignal only outputs positive amplitudes.) It seems that SeismoSignal should return a phase angle in the correct quadrant using a function like ATAN2 instead.

2) The Help System also indicates that the argument of the ATAN function call for the phase angle is the ratio Re/Im. This is inverted from the typical definition of a phase angle in the complex plane, where the imaginary axis is drawn vertically and the real axis horizontally. I can't tell from the output if this is actually a bug in the software, or just a typo in the Help System, because of my next concern.

3) I have compared SeismoSignal Fourier Spectra output to analyses using two different FFT libraries. The other two libraries agreed with each other on the phase angle results, but SeismoSignal's phase angles were different. I tried using the ATAN function instead of ATAN2 and using both Re/Im and Im/Re, but I was not able to get the same results as SeismoSignal. If this is because of an additional bug, somehow the amplitude is not affected.

[seismosoft]

Hello TomPaceHDR.
Indeed the ATAN(Re/Im) function is used for computing the Phase angle in SeismoSignal. The correct function along with a more refined algorithm to calculate the phase angle will be scheduled for a following version of SeismoSignal.
Seismosoft Support