seewave (version 1.6.3)

ceps: Cepstrum or real cepstrum

Description

This function returns the cepstrum of a time wave allowing fundamental frequency detection.

Usage

ceps(wave, f, 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", ...)

Value

• 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).

Warning

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

Details

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 calcuated as follows: $$C(s) = Re[FFT^{-1}(\log{(|FFT(s)|)]}$$ 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 co0rdinate. 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.

References

Oppenheim, A.V. and Schafer, R.W. 2004. From frequency to quefrency: a history of the cepstrum. Signal Processing Magazine IEEE, 21: 95-106.

See Also

cepstro, fund, autoc

Examples

data(sheep)
ceps(sheep,f=8000,at=0.4,wl=1024)