I don't see any benefit to averaging parts of the signal. If you average within a single revolution, you will lose your phase information. There is no benefit of averaging sections of repeated signals either. Just do a large FFT for each revolution and average them.
FYI, you could average the signals themselves or the complex FFTs for repeated signals. I don't recommend averaging magnitude and phase in this case. Bruce ------------------------------------------ Bruce Ammons Ammons Engineering www.ammonsengineering.com (810) 687-4288 Phone (810) 687-6202 Fax -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Gerd Rech Sent: Wednesday, February 04, 2004 10:26 AM To: Bruce Ammons Cc: Info LabVIEW Subject: AW: [W6.1] RMS averaging with "FFT Spectrum (Mag-Phase).vi" I have a phase reference pulse once per rev which starts the acquisition. So I should get consistent phase readings for repeated measurements. However, I was wondering if it would make sense to average parts of the signal(using overlapping segments) for speeding up the averaging process. The idea is to make as much use as possible out of the data that I get into the PC. Gerd -----Ursprungliche Nachricht----- Von: Bruce Ammons [mailto:[EMAIL PROTECTED] Gesendet: Mittwoch, 4. Februar 2004 15:27 An: 'Gerd Rech'; [EMAIL PROTECTED] Betreff: RE: [W6.1] RMS averaging with "FFT Spectrum (Mag-Phase).vi" The only way to get meaningful phase is to start your acquisition at the same phase for every segment. An example of this would be an encoder pulse. If each acquisition starts at a once per rev pulse from the encoder, they will all have the same phase components. Another possibility is doing order tracking, where there is a fixed number of samples per revolution. If you shift your window by the number of samples per revolution, you will get the same phase again. Any time you have a steady stream of data with no reference point, the phase data is essentially useless. If it is a repeating signal you should be able to identify a reference point. I suppose if you don't have a hardware signal, you could use convolution to identify repeating cycles of data. If phase is important, you should have a reference signal. Bruce ------------------------------------------ Bruce Ammons Ammons Engineering www.ammonsengineering.com (810) 687-4288 Phone (810) 687-6202 Fax -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Gerd Rech Sent: Wednesday, February 04, 2004 3:36 AM To: [EMAIL PROTECTED] Subject: Re: [W6.1] RMS averaging with "FFT Spectrum (Mag-Phase).vi" Hi folks, I know the "overlapping average" technology from signal analysers. In those cases I used them up to now, phase was not relevant. Now I have an idea about a different use where phase would be important. Scott's comment that phase would be meaningless if overlapping averaging is used is making me thinking. What about this: 1. Cut the long waveform stream into a number of (overlapping) pieces. 2. Use the FFT vi for each piece, which will produce amplitudes and phases for each frequency bin. 3. Average apmlitude and phase for each frequency bin separately. Would this create meaningful phase? I would guess yes, as all pieces were acquired in a consistant stream of data originally. Seems that my mathematical understanding does not reach far enough to understand this completely. Cheers Gerd
