seewave (version 2.2.4)

bwfilter: Butterworth frequency filter

Description

This function is a Butterworth frequency filter that filters out a selected frequency section of of a time wave (low-pass, high-pass, low-stop, high-stop, bandpass or bandstop frequency filter).

Usage

bwfilter(wave, f, channel = 1, n = 1, from = NULL, to = NULL,
bandpass = TRUE, listen = FALSE, output = "matrix")

Value

A new wave is returned. The class of the returned object is set with the argument output.

Details

The order of the filter determines the value of the roll-off value, that is the dB decrease per octave of the transfer function. A filter of order n will have a transfer function with a roll-off value of - n*6 dB.

References

Stoddard, P. K. (1998). Application of filters in bioacoustics. In: Hopp, S. L., Owren, M. J. and Evans, C. S. (Eds), Animal acoustic communication. Springer, Berlin, Heidelberg,pp. 105-127.

See Also

ffilter, bwfilter, preemphasis, lfs, afilter

Examples

require(signal)
f <- 8000
a <- noisew(f=f, d=1)
## low-pass
# 1st order filter
res <- bwfilter(a, f=f, n=1, to=1500)
# 8th order filter
res <- bwfilter(a, f=f, n=8, to=1500)
## high-pass
res <- bwfilter(a, f=f, from=2500)
## band-pass
res <- bwfilter(a, f=f, from=1000, to=2000)
## band-stop
res <- bwfilter(a, f=f, from=1000, to=2000,bandpass=FALSE)