spec {seewave}

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

See Also

meanspec, fpeaks, localpeaks, dynspec, corspec, fft.

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")