| ceps {seewave} | R Documentation |
This function returns the cepstrum of a time wave allowing fundamental frequency detection.
ceps(wave, f, channel = 1, phase = FALSE, wl = 512, at = NULL, from = NULL, to = NULL, tidentify = FALSE, fidentify = FALSE, col = "black", cex = 1, plot = TRUE, qlab = "Quefrency (bottom: s, up: Hz)", alab = "Amplitude", qlim = NULL, alim = NULL, type = "l", ...)
wave |
an R object. |
f |
sampling frequency of |
channel |
channel of the R object, by default left channel (1). |
phase |
if |
wl |
if |
at |
position where to compute the cepstrum (in s). |
from |
start position where to compute the cepstrum (in s). |
to |
end position to compute the cepstrum (in s). |
tidentify |
to identify time values on the plot with the help of a cursor. |
fidentify |
to identify frequency values on the plot with the help of a cursor. |
col |
colour of the cepstrum. |
cex |
pitch size of the cepstrum. |
plot |
logical, if |
qlab |
title of the quefrency axis (in s). |
alab |
title of the amplitude axis. |
qlim |
range of quefrency axis. |
alim |
range of amplitude axis. |
type |
if |
... |
other |
The cepstrum of a time wave is the inverse Fourier transform of the logarithm
of the Fourier transform. The cepstrum of a wave s is then calculated as follows:
C(s) = Re(invfft(log(abs(fft(s)))))
The independent variable of a cepstral graph is called the quefrency.
The quefrency is a measure of time, though not in the sense of a signal
in the time domain. A correspondence with the frequency domain is obtained
by simply computing the reverse of the temporal x coordinate. For instance if
a peak appears at 0.005 s, this reveals a frequency peak at 200 Hz (=1/0.005).
This explain the two scales plotted when plot is TRUE.
If at, from or to are FALSE then ceps
computes the cepstrum of the whole signal.
When using tidentify or tidentify, press ‘stop’
tools bar button to return values in the console.
When plot is FALSE, ceps returns the cesptral profile as a two-column matrix, the first column corresponding to quefrency (x-axis) and the second
corresponding to amplitude (y-axis).
The argument peaks is no more available
(version > 1.5.6). See the function fpeaks
for peak(s) detection.
Cepstral analysis is mainly used in speech processing.
This analysis allows to extract the fundamental frequency, see the examples.
This function is based on fft.
Jerome Sueur sueur@mnhn.fr
Oppenheim, A.V. and Schafer, R.W. 2004. From frequency to quefrency: a history of the cepstrum. Signal Processing Magazine IEEE, 21: 95-106.
data(sheep) par(mfrow=c(2,1)) # phase not taken into account ceps(sheep,f=8000,at=0.4,wl=1024) # phase taken into account ceps(sheep,f=8000,at=0.4,wl=1024, phase=TRUE)