evolfft: Spectrogram fft

In RSEIS: Seismic Time Series Analysis Tools

Spectrogram fft

Description

Spectrogram using simple fft (Gabor Transform)

Usage

evolfft(a, dt = 0, Nfft = 0, Ns = 0, Nov = 0, fl = 0, fh = 10, pcttap =
0.05, adjust=TRUE )

Arguments

a	signal
dt	sample rate interval (s)
Nfft	Number of points in fft
Ns	NUmber of sample in sub-window
Nov	number of sample to overlap
fl	low frequency to display
fh	high frequency to display
pcttap	Percent cosine taper for each window
adjust	logical, if TRUE adjust the parameters so the plot looks good (DEFAULT). If FALSE, keep user parameters.

Details

This is a duplication of the spectrogram function in matlab which applies Welsh's Method. Each mini-window is tapered with a cosine window.

Value

List

sig	input signal
dt	deltat
wpars	input parameters
DSPEC	spectrum image
freqs	output frequencies (y axis)
tims	output times (x-axis)

Note

Parameter adjust is by default TRUE so that the choice of Ns, Nov, and kcol will be optimized, more or less. Set this logical to FALSE to force the function to use user input parameters.

Author(s)

Jonathan M. Lees<jonathan.lees.edu>

See Also

evolMTM, evolAR, MTM.drive

Examples

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")

RSEIS documentation built on Aug. 19, 2023, 5:07 p.m.