RSEIS (version 4.2-4)

butfilt: Butterworth filter

Description

Design and apply butterworth low/high/band pass filters.

Usage

butfilt(a, fl=0, fh=0.5, deltat=1, type="BP", proto="BU",
 npoles=5, chebstop=30.0, trbndw=0.3, RM=FALSE, zp=TRUE )

Value

Filtered time series.

Arguments

a

vector signal

fl

low frequency cut-off, default=0

fh

high frequency cut-off, DEFAULT= (1/2dt)

deltat

sample rate, s, deFAULT=1

type

type of filter, one of c("LP", "HP","BP" ,"BR" ), DEFAULT="BP"

proto

prototype, c("BU", "BE" , "C1" ,"C2"), DEFAULT="BU"

npoles

number of poles or order, DEFAULT=5

chebstop

Chebyshev stop band attenuation, DEFAULT=30.0

trbndw

Chebyshev transition bandwidth, DEFAULT=0.3

RM

Remove mean value from trace, default=FALSE

zp

zero phase filter, default=TRUE

Author

originally written in FORTRAN by David Harris, converted to C and modified by Jonathan M. Lees<[e-mail]>

Details

Creation of butfilt is a described by the following arguments:

LP

low pass

HP

high pass

BP

band pass

BR

band reject

BU

Butterworth

BE

Bessel

C1

Chebyshev type 1

C2

Chebyshev type 2

Arguments chebstop , trbndw are ignored for non-chebyshev filters. LP and HP filters are seet by specifying fl for HP filters and fh for LP filters, the other argumentin each case is ignored.

Mean values should be removed prior to calling this function, and then set RM=FALSE. This is true especially if tapering is applied prior to filtering.

Zero phase filter is achived by running filter back and forth. Otherwise a single pass is returned. This should be equivalent to package signal filtfilt (from MATLAB).

References

Harris, D., 1990: XAPiir: A recursive digital filtering package. United States: N. p., Web. doi:10.2172/6416972.

See Also

AUGMENTbutfilt

Examples

data(CE1)

ts1  <-  CE1$y
zz  <-  butfilt(ts1, fl=1, fh=15,  deltat=CE1$dt, type="LP" ,  proto="BU",
npoles=5 )



###  try plotting:

### the above, by default, is zero phase.
#####  next filter with non-zero-phase
z2  <-  butfilt(ts1, fl=1, fh=15,  deltat=CE1$dt, type="LP" ,  proto="BU",
npoles=5, zp=FALSE )
ex = seq(from=0, by=CE1$dt, length=length(ts1))

plot(ex,  ts1, type='l')
lines(ex, zz, col='red')
lines(ex, z2, col='blue')


plot(ex[ex<0.5],  ts1[ex<0.5], type='l')
lines(ex[ex<0.5], zz[ex<0.5], col='red')
lines(ex[ex<0.5], z2[ex<0.5], col='blue')