R: Frequency spectrum of a time wave

spec {seewave}

R Documentation

Frequency spectrum of a time wave

Description

This function returns the frequency spectrum (i.e. the relative amplitude of the frequency content) of a time wave. Results can be obtained either as absolute or dB data.

Usage

spec(wave, f, channel = 1, wl = 512, wn = "hanning", fftw = FALSE, norm = TRUE,
scaled = FALSE, PSD = FALSE, PMF = FALSE, correction="none", dB = NULL, dBref = NULL,
at = NULL, from = NULL, to = NULL,
identify = FALSE, col = "black", cex = 1,
plot = 1, flab = "Frequency (kHz)",
alab = "Amplitude", flim = NULL,
alim = NULL, type="l",...)

Arguments

`wave`	an R object.
`f`	sampling frequency of `wave` (in Hz). Does not need to be specified if embedded in `wave`.
`channel`	channel of the R object, by default left channel (1).
`wl`	if `at` is not null, length of the window for the analysis (by default = 512).
`wn`	window name, see `ftwindow` (by default `"hanning"`).
`fftw`	if `TRUE` calls the function `FFT` of the library `fftw` for faster computation. See Notes of the function `spectro`.
`norm`	if `TRUE` the spectrum is normalised by its maximum.
`scaled`	if `TRUE` the spectrum is scaled by the length of the FFT.
`PSD`	if `TRUE` return Power Spectrum Density, i. e. the square of the spectrum.
`PMF`	if `TRUE` return Probability Mass Function, i. e. the probability distribution of frequencies.
`correction`	a character vector of length 1 to apply an amplitude ("amplitude") or an energy ("energy") correction to the FT window. This argument is useful only when one wish to obtain absolute values that is when `norm=FALSE`, `scaled=FALSE`, and `PMF=FALSE`. By default no correction is applied ("none").
`dB`	a character string specifying the type dB to return: "max0" for a maximum dB value at 0, "A", "B", "C", "D", and "ITU" for common dB weights.
`dBref`	a dB reference value when `dB` is not `NULL`. `NULL` by default but should be set to 2*10e-5 for a 20 microPa reference (SPL).
`at`	position where to compute the spectrum (in s).
`from`	start mark where to compute the spectrum (in s).
`to`	end mark where to compute the spectrum (in s).
`identify`	to identify frequency and amplitude values on the plot with the help of a cursor.
`col`	colour of the spectrum.
`cex`	pitch size of the spectrum.
`plot`	if `1` returns frequency on x-axis, if `2` returns frequency on y-axis, (by default `1`).
`flab`	title of the frequency axis.
`alab`	title of the amplitude axis.
`flim`	range of frequency axis.
`alim`	range of amplitude axis.
`type`	if `plot` is `TRUE`, type of plot that should be drawn. See `plot` for details (by default "l" for lines).
`...`	other `plot` graphical parameters.

Details

If at, from or to are FALSE then spec computes the spectrum of the whole signal.

Value

This function returns a two-column matrix, the first column corresponding to the frequency axis, the second column corresponding to the amplitude axis.
If identify is TRUE, spec returns a list with two elements:

freq

the frequency of the points chosen on the spectrum

amp

the relative amplitude of the points chosen on the spectrum

Warning

The argument peaks is no more available (version > 1.5.6). See the function fpeaks for peak(s) detection.

Note

This function is based on fft.

Author(s)

Jerome Sueur

Examples

data(tico)
# spectrum of the whole signal, in absolute or dB amplitude,
# horizontaly or vertically
op<-par(mfrow=c(2,2))
spec(tico,f=22050)
spec(tico,f=22050,col="red",plot=2)
spec(tico,f=22050,dB="max0",col="blue")
spec(tico,f=22050,dB="max0",col="green",plot=2)
par(op)
# an indirect way to compare spectra 
a<-spec(tico,f=22050,wl=512,at=0.2,plot=FALSE)
b<-spec(tico,f=22050,wl=512,at=0.7,plot=FALSE)
c<-spec(tico,f=22050,wl=512,at=1.1,plot=FALSE)
d<-spec(tico,f=22050,wl=512,at=1.6,plot=FALSE)
all<-cbind(a[,2],b[,2],c[,2],d[,2])
matplot(x=a[,1],y=all,yaxt="n",
    xlab="Frequency (kHz)",ylab="Amplitude",xaxs="i",type="l")
legend(8,0.8,c("Note A","Note B", "Note C", "Note D"),bty="o",
    lty=c(1:4),col=c(1:4))
# spectrum from a particular position to another one
op<-par(mfrow=c(2,1))
oscillo(tico,f=22050)
abline(v=c(0.5,0.9),col="red",lty=2)
spec(tico,f=22050,wl=512,from=0.5,to=0.9,col="red")
title("Spectrum of the note B")
par(op)
# spectrum and spectrogram
data(orni)
orni1<-cutw(orni,f=22050,from=0.32,to=0.39)
layout(matrix(c(1,2),nc=2),widths=c(3,1))
par(mar=c(5,4,3,0.5))
spectro(orni1,f=22050,wl=128,zp=8,ovlp=85,scale=FALSE)
par(mar=c(5,1,3,0.5))
spec(orni1,f=22050,col="red",plot=2,flab="",yaxt="n")

[Package seewave version 2.1.6 Index]