seewave (version 2.1.6)

fpeaks: Frequency peak detection

Description

This function searches for peaks of a frequency spectrum.

Usage

fpeaks(spec, f = NULL,
nmax = NULL, amp = NULL, freq = NULL, threshold = NULL,
mel =FALSE,
plot = TRUE, title = TRUE,
xlab = NULL, ylab = "Amplitude",
labels = TRUE, digits = 2,
legend = TRUE, collab = "red", ...)

Arguments

spec

a data set resulting of a spectral analysis obtained with spec or meanspec. Can be in dB.

f

sampling frequency of spec (in Hz). Not requested if the first column of spec contains the frequency axis.

nmax

maximal number of peaks detected. Overrides amp and freq. See details.

amp

amplitude slope parameter, a numeric vector of length 2. Refers to the amplitude slopes of the peak. The first value is the left slope and the second value is the right slope. Only peaks with higher slopes than threshold values will be kept. See details.

freq

frequency threshold parameter (in Hz). If the frequency difference of two successive peaks is less than this threshold, then the peak of highest amplitude will be kept only. See details.

threshold

amplitude threshold parameter. Only peaks above this threshold will be considered. See details.

mel

a logical, if TRUE the (htk-)mel scale is used.

plot

logical, if TRUE, a plot showing the peaks is returned.

title

logical, if TRUE add the number of peaks detected as a plot title.

xlab

label of the x-axis.

ylab

label of the y-axis.

labels

logical, if TRUE peak labels are plotted.

digits

if labels is TRUE, the number of decimal places (round) for the peak labels.

legend

logical, if TRUE a legend returning the different selection parameters (nmax, amp, freq, threshold, threshold) is added to the plot.

collab

labels color.

…

other plot graphical parameters.

Value

A two-column matrix, the first column corresponding to the frequency values (x-axis) and the second column corresponding to the amplitude values (y-axis) of the peaks.

Details

Here are some details regarding the different selection parameters:

• nmax: this parameter is to be used if you wish to get a specific number of peaks. The peaks selected are those with the highest slopes. It then does not work in conjunction with the other parameters.

• freq: this parameter allows to remove from the selection successive peaks with a small frequency difference. Imagine you have two successive peaks at 1200 Hz and 1210 Hz and at 0.5 and 0.25 in amplitude. If you set freq to 50 Hz, then only the first peak will be kept.

• amp: this parameter allows to remove from the selection peaks with low slopes. You can make the selection on both slopes or on a single one. Imagine you have an asymetric peak with a 0.01 left slope and a 0.02 right slope. The peak will be discarded for the following settings: both values higher than 0.02 (e.g. amp = c(0.03,0.04)), the first value higher than 0.01 (e.g. amp = c(0.02,0.001)), the second value higher than 0.02 (e.g. amp = c(0.001,0.03)). If you do not want apply the selection on one of the slope use 0. For instance, a selection on the left slope only will be achieved with: amp = c(0.02,0).

• threshold: this parameter can be used to do a rough selection on the spectrum. Peaks with an amplitude value (not a slope) lower than this threshold will be automatically discarded. This can be useful when you want to remove peaks of a low-amplitude background noise.

See Also

localpeaks, meanspec, spec

Examples

# NOT RUN {
data(tico)
spec <- meanspec(tico, f=22050, plot=FALSE)
specdB <- meanspec(tico, f=22050, dB="max0", plot=FALSE)
# all peaks
fpeaks(spec)
# 10 highest peaks
fpeaks(spec, nmax=10)
# highest peak (ie dominant frequency)
fpeaks(spec, nmax=1)
# peaks that are separated by more than 500 Hz
fpeaks(spec, freq=500)
# peaks with a left slope higher than 0.1
fpeaks(spec, amp=c(0.1,0))
# peaks with a right slope higher than 0.1
fpeaks(spec, amp=c(0,0.1))
# peaks with left and right slopes higher than 0.1
fpeaks(spec, amp=c(0.1,0.1))
# peaks above a 0.5 threshold
fpeaks(spec, threshold=0.5)
# peaks of a dB spectrum with peaks showing slopes higher than 3 dB
fpeaks(specdB, amp=c(3,3))
# comparing different parameter settings
meanspec(tico, f=22050)
col <- c("#ff000090","#0000ff75","#00ff00")
cex <- c(2,1.25,1.5)
pch <- c(19,17,4)
title(main="Peak detection \n (spectrum with values between 0 and 1)")
res1 <- fpeaks(spec, plot = FALSE)
res2 <- fpeaks(spec, amp=c(0.02,0.02), plot =FALSE)
res3 <- fpeaks(spec, amp=c(0.02,0.02), freq=200, plot = FALSE)
points(res1, pch=pch[1], col=col[1], cex=cex[1])
points(res2, pch=pch[2], col=col[2], cex=cex[2])
points(res3, pch=pch[3], col=col[3], cex=cex[3])
legend("topright", legend=c("all peaks","amp", "amp & freq"), pch=pch,
pt.cex=cex, col=col, bty="n")
# example with a cepstral spectrum
data(sheep)
res <- ceps(sheep,f=8000,at=0.4,wl=1024,plot=FALSE)
fpeaks(res, nmax=4, xlab="Quefrency (s)")
# melscale
require(tuneR)
mel <- melfcc(sheep, nbands = 256, dcttype = "t3", fbtype = "htkmel", spec_out=TRUE)
melspec.mean <- apply(mel$aspectrum, MARGIN=2, FUN=mean)
melspec.mean <- melspec.mean/max(melspec.mean) # [0,1] scaling 
fpeaks(melspec.mean, nmax=4, f=8000, mel=TRUE)
fpeaks(melspec.mean, freq=4, f=8000, mel=TRUE) # freq in Hz!
fpeaks(melspec.mean, threshold=0.3, f=8000, mel=TRUE)
fpeaks(melspec.mean, amp=c(0.1,0.1), f=8000, mel=TRUE)
# }