evolfft {RSEIS}R Documentation

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 )

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

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)

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")


[Package RSEIS version 2.3-3 Index]