seewave (version 2.2.4)

spectro: 2D-spectrogram of a time wave

Description

This function returns a two-dimension spectrographic representation of a time wave. The function corresponds to short-term Fourier transform. An amplitude contour plot can be overlaid.

Usage

spectro(wave, f, channel = 1, wl = 512, wn = "hanning", zp = 0,
ovlp = 0, noisereduction = NULL, fastdisp = FALSE,
complex = FALSE, norm = TRUE, correction="none",
fftw = FALSE, dB = "max0", dBref = NULL, plot = TRUE,
flog = FALSE, grid = TRUE, osc = FALSE, scale = TRUE, cont = FALSE,
collevels = NULL, palette = spectro.colors,
contlevels = NULL, colcont = "black",
colbg = "white", colgrid = "black",
colaxis = "black", collab="black",
cexlab = 1, cexaxis = 1, 
tlab = "Time (s)",
flab = "Frequency (kHz)",
alab = "Amplitude",
scalelab = "Amplitude\n(dB)",
main = NULL,
scalefontlab = 1, scalecexlab =0.75,
axisX = TRUE, axisY = TRUE, tlim = NULL, trel = TRUE,
flim = NULL, flimd = NULL,
widths = c(6,1), heights = c(3,1),
oma = rep(0,4),
listen=FALSE,
...)

Value

This function returns a list of three items:

time

a numeric vector corresponding to the time axis.

freq

a numeric vector corresponding to the frequency axis.

amp

a numeric or a complex matrix corresponding to the amplitude values. Each column is a Fourier transform of length wl/2.

Details

Following Heisenberg uncertainty principle, the short-term Fourier transform cannot be precised in both time and frequency. The temporal and frequency precisions of the function are actually dependent of the wl value. Choosing a high wl value will increase the frequency resolution but reduce the temporal one, and vice versa. The frequency precision is obtained by calculating the ratio f/wl, and the temporal precision is obtained by calculating the reverse ratio wl/f. This problem can be reduced in some way with zp that adds 0 values on both sides of the analysis window. This increases frequency resolution without altering time resolution.
Any colour palette can be used. In particular, it is possible to use other palettes coming with seewave: temp.colors, reverse.gray.colors.1, reverse.gray.colors.2, reverse.heat.colors, reverse.terrain.colors, reverse.topo.colors, reverse.cm.colors corresponding to the reverse of heat.colors, terrain.colors, topo.colors, cm.colors.
Use locator to identify points. The noise reduction using the argument noisereduction is an image filter, not a signal filter. The principle consists in subtracting each spectrogram row or column by its median. Noise reduction alters energy conservation, it should then be used for visual display only.

References

Hopp, S. L., Owren, M. J. and Evans, C. S. (Eds) 1998. Animal acoustic communication. Springer, Berlin, Heidelberg.

See Also

ggspectro, spectro3D, lts, dynspec, wf, oscillo, dBscale, fft.

Examples

if (FALSE) {
data(tico)
data(pellucens)
# simple plots
spectro(tico,f=22050)
spectro(tico,f=22050,osc=TRUE)
spectro(tico,f=22050,scale=FALSE)
spectro(tico,f=22050,osc=TRUE,scale=FALSE)
# change the dB scale by setting a different dB reference value (20microPa)
spectro(tico,f=22050, dBref=2*10e-5)
# unnormalised spectrogram with a linear amplitude scale
spectro(tico, dB=NULL, norm=FALSE, scale=FALSE)
# manipulating wl
op<-par(mfrow=c(2,2))
spectro(tico,f=22050,wl=256,scale=FALSE)
title("wl = 256")
spectro(tico,f=22050,wl=512,scale=FALSE)
title("wl = 512")
spectro(tico,f=22050,wl=1024,scale=FALSE)
title("wl = 1024")
spectro(tico,f=22050,wl=4096,scale=FALSE)
title("wl = 4096")
par(op)
# vertical zoom using flim
spectro(tico,f=22050, flim=c(2,6))
spectro(tico,f=22050, flimd=c(2,6))
# a full plot
pellu2<-cutw(pellucens,f=22050,from=1,plot=FALSE)
spectro(pellu2,f=22050,ovlp=85,zp=16,osc=TRUE,
    cont=TRUE,contlevels=seq(-30,0,20),colcont="red",
    lwd=1.5,lty=2,palette=reverse.terrain.colors)
# black and white spectrogram 
spectro(pellu2,f=22050,ovlp=85,zp=16,
    palette=reverse.gray.colors.1)
# colour modifications
data(sheep)
spectro(sheep,f=8000,palette=temp.colors,collevels=seq(-115,0,1))
spectro(pellu2,f=22050,ovlp=85,zp=16,
palette=reverse.cm.colors,osc=TRUE,colwave="orchid1") 
spectro(pellu2,f=22050,ovlp=85,zp=16,osc=TRUE,palette=reverse.heat.colors,
colbg="black",colgrid="white", colwave="white",colaxis="white",collab="white")
}