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Spectrogram using simple fft (Gabor Transform)
evolfft(a, dt = 0, Nfft = 0, Ns = 0, Nov = 0, fl = 0, fh = 10, pcttap =
0.05, adjust=TRUE )
List
input signal
deltat
input parameters
spectrum image
output frequencies (y axis)
output times (x-axis)
signal
sample rate interval (s)
Number of points in fft
NUmber of sample in sub-window
number of sample to overlap
low frequency to display
high frequency to display
Percent cosine taper for each window
logical, if TRUE adjust the parameters so the plot looks good (DEFAULT). If FALSE, keep user parameters.
Jonathan M. Lees<jonathan.lees.edu>
This is a duplication of the spectrogram function in matlab which applies Welsh's Method. Each mini-window is tapered with a cosine window.
evolMTM, evolAR, MTM.drive
data(CE1)
#### plot signals
plot(CE1$x, CE1$y, type='l')
### set parameters
Nfft<-1024 ### fft length
Ns<-250 ### number of samples in a window
Nov<-240 ### number of samples of overlap per window
fl<-0 ### low frequency to return
fh<-1/(2*CE1$dt) ### high frequency to return
######## calculate the evolutive fft (Gabor Transform)
EV <- evolfft(CE1$y, dt =CE1$dt , Nfft = Nfft, Ns =Ns , Nov =Nov , fl =fl
, fh = 25)
### plot image, but it does not look too interesting
image(EV$DSPEC)
### plot Gabor transform with special function
PE <- plotevol(EV, log=0, fl=0.01, fh=100, col=rainbow(100), ygrid=FALSE,
STAMP="", STYLE="fft")
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