R: Mean frequency spectrum of a time wave

meanspec {seewave}

R Documentation

Mean frequency spectrum of a time wave

Description

This function returns the mean frequency spectrum (i.e. the mean relative amplitude of the frequency distribution) of a time wave. Results can be expressed either in absolute or dB data.

Usage

meanspec(wave, f, channel = 1, wl = 512, wn = "hanning", ovlp = 0, fftw = FALSE,
norm = TRUE, PSD = FALSE, PMF = FALSE, FUN = mean, correction = "none", dB = NULL,
dBref = 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`	length of the window for the analysis (even number of points, by default = 512).
`wn`	window name, see `ftwindow` (by default `"hanning"`).
`ovlp`	overlap between two successive analysis windows (in %).
`fftw`	if `TRUE` calls the function `FFT` of the library `fftw`. See Notes of `spectro`.
`norm`	if `TRUE` the mean spectrum is normalised (i. e. scaled) by its maximum.
`PSD`	if `TRUE` return Power Spectra Density, i. e. the square of the spectra.
`PMF`	if `TRUE` return Probability Mass Function, i. e. the probability distribution of frequencie.
`FUN`	the function to apply on the rows of the STFT matrix, by default `mean` for a mean spectrum but could be other as `median` or `var` for a median spectrum or variance spectrum.
`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` 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).
`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.
`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 (in kHz).
`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

See examples of spec. This function is based on fft.

Value

If plot is FALSE, meanspec returns a two columns 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

The argument fftw can be used to try to speed up process time. When set to TRUE, the Fourier transform is computed through the function FFT of the package fftw. This pacakge is a wrapper around the fastest Fourier transform of the free C subroutine library FFTW (http://www.fftw.org/). FFT should be then installed on your OS.

Author(s)

Jerome Sueur sueur@mnhn.fr

Examples

data(orni)
# compute the mean spectrum of the whole time wave
meanspec(orni,f=22050)
# compute the mean spectrum of a time wave section (from 0.32 s to 0.39 s)
meanspec(orni,f=22050,from=0.32,to=0.39)
# different window lengths
op<-par(mfrow=c(3,1))
meanspec(orni,f=22050,wl=256)
title("wl=256")
meanspec(orni,f=22050,wl=1024)
title("wl=1024")
meanspec(orni,f=22050,wl=4096)
title("wl=4096")
par(op)
# different overlap values (almost no effects here...)
op<-par(mfrow=c(3,1))
meanspec(orni,f=22050)
title("ovlp=0")
meanspec(orni,f=22050,ovlp=50)
title("ovlp=50")
meanspec(orni,f=22050,ovlp=95)
title("ovlp=95")
par(op)
# use of flim to zoom in
op<-par(mfrow=c(2,1))
meanspec(orni,f=22050)
title("zoom in")
meanspec(orni,f=22050,wl=512,flim=c(4,6))
par(op)
# comparaison of spectrum and mean spectrum
op<-par(mfrow=c(2,1))
spec(orni,f=22050)
title("spec()")
meanspec(orni,f=22050)
title("meanspec()")
par(op)
# log scale on frequency axis
meanspec(orni, f=22050, log="x")
# median spectrum
meanspec(orni,f=22050, FUN=median)
# variance spectrum
meanspec(orni,f=22050, FUN=var)

[Package seewave version 2.1.6 Index]