RSEIS (version 2.1-6)

evolfft: Spectrogram fft

Description

Spectrogram using simple fft (Gabor Transform)

Usage

evolfft(a, dt = 0, Nfft = 0, Ns = 0, Nov = 0, fl = 0, fh = 10)

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

Value

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

Details

This is a duplication of the spectrogram function in matlab which applies Welsh's Method.

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")