bwfilter {seewave}

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")

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).

n

Order of the filter. See details.

from

start frequency (in Hz) where to apply the filter.

to

end frequency (in Hz) where to apply the filter.

bandpass

if TRUE a band-pass filter is applied between from and to, if not NULL a band-stop filter is applied between from and to (by default NULL).

listen

if TRUE the new sound is played back.

output

character string, the class of the object to return, either "matrix", "Wave", "Sample", "audioSample" or "ts".

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.

Value

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

Note

This function mainly uses the functions filter() and filtfilt() from the package signal

Author(s)

Jerome Sueur, functions filter() and filtfilt() from the package signal.

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)