how to understand fft results

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Max Higginbotham
Max Higginbotham 2016-5-6
回答： Star Strider 2016-5-6
Hi, I have a real waveform from a pressure sensor in csv form which exhibits pressure pulsations. I can import the data and do an fft on the data to get the frequency contribution for the whole signal. But, what I need to find is the total (peak to dip) pressure pulsation at each frequency. If I take the mean pressure for the whole sample from each data point so that I get the plus/minus variation about the mean and then do an fft analysis on this data, is the fft going to tell me the total contribution (peak to dip) at each frequency component, or just the positive half (zero to peak) of the contribution at each frequency.

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Star Strider
Star Strider 2016-5-6
The Fourier transform is probably going to give you the mean amplitude at each frequency. If you want to find the peak-to-dip pressure pulsation at each frequency, you have to use a bandpass filter for those frequencies, then analyse the time-domain data.
There are several ways to design filters, my procedure is here: How to design a lowpass filter for ocean wave data in Matlab? Filter design is heuristic, so you will have to experiment with each filter to get the result you want.

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