spectrogram function

Spectrogram

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.

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.

Returns

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])