spectrogram {EMD}

Spectrogram

Description

This function produces image of amplitude by time index and instantaneous frequency. The horizontal axis represents time, the vertical axis is instantaneous frequency, and the color of each point in the image represents amplitude of a particular frequency at a particular time.

Usage

spectrogram(amplitude, freq, tt = NULL, multi = FALSE, 
nlevel = NULL, size = NULL) 

Arguments

amplitude

vector or matrix of amplitudes for multiple signals

freq

vector or matrix of instantaneous frequencies for multiple signals

tt

observation index or time index

multi

specifies whether spectrograms of multiple signals are separated or not.

nlevel

the number of color levels used in legend strip

size

vector of image size.

Details

This function produces image of amplitude by time index and instantaneous frequency. The horizontal axis represents time, the vertical axis is instantaneous frequency, and the color of each point in the image represents amplitude of a particular frequency at a particular time.

Value

image

References

Huang, N. E., Shen, Z., Long, S. R., Wu, M. L. Shih, H. H., Zheng, Q., Yen, N. C., Tung, C. C. and Liu, H. H. (1998) The empirical mode decomposition and Hilbert spectrum for nonlinear and nonstationary time series analysis. Proceedings of the Royal Society London A, 454, 903–995.

See Also

hilbertspec.

Examples

tt <- seq(0, 0.1, length = 2001)[1:2000]           
f1 <- 1776; f2 <- 1000
xt <- sin(2*pi*f1*tt) * (tt <= 0.033 | tt >= 0.067) + sin(2*pi*f2*tt)
 
### Before treating intermittence
interm1 <- emd(xt, tt, boundary="wave", max.imf=2, plot.imf=FALSE)  
### After treating intermittence
interm2 <- emd(xt, tt, boundary="wave", max.imf=2, plot.imf=FALSE, 
interm=0.0007)

par(mfrow=c(2,1), mar=c(2,2,2,1))
test1 <- hilbertspec(interm1$imf)
spectrogram(test1$amplitude[,1], test1$instantfreq[,1])

test2 <- hilbertspec(interm2$imf, tt=tt)
spectrogram(test2$amplitude[,1], test2$instantfreq[,1])