# Apply Butterworth filter The `butterworth` method of `Trace` objects returns a new `Trace` where data in the `@data` slot have been modified by applying a Butterworth filter. methods ```r butterworth(x, n, low, high, type) ``` ## Arguments - `x`: a `Trace` object - `n`: filter order - `low`: frequency used in low- or stop/band-pass filters - `high`: frequency used in high or stop/band-pass filters - `type`: type of filter -- `'low', 'high', 'pass'` or `'stop'` ## Details This method creates a Butterworth filter with the specified characteristics and applies it to the Trace data. When only `n` and `low` are specified, a high pass filter is applied. When only `n` and `high` are specified, a low pass filter is applied. When `n` and both `low` and `high` are specified, a band pass filter is applied. To apply a band stop filter you must specify `n`, `low`, `high` and `type='stop'` ## Returns A new `Trace` object is returned. ## Author(s) Jonathan Callahan jonathan@mazamascience.com ## See Also signal::butter, signal::filter ## Examples ```r ## Not run: # Open a connection to EarthScope webservices iris <- new("IrisClient") # Compare to the results in figure 2a of # # "Determination of New Zealand Ocean Bottom Seismometer Orientation # via Rayleigh-Wave Polarization", Stachnik et al. # # http://srl.geoscienceworld.org/content/83/4/704 # # (note: since publication, ZU.NZ19..BH1 has been renamed BH2 and ZU.NZ19..BH2 has been renamed BH1) starttime <- as.POSIXct("2009-02-18 22:01:07",tz="GMT") endtime <- starttime + 630 verticalLines <- starttime + seq(30,630,100) # Get data stZ <- getSNCL(iris,"ZU.NZ19..BHZ",starttime,endtime) st2 <- getSNCL(iris,"ZU.NZ19..BH2",starttime,endtime) st1 <- getSNCL(iris,"ZU.NZ19..BH1",starttime,endtime) # Demean, Detrend, Taper trZ <- DDT(stZ@traces[[1]],TRUE,TRUE,0.05) tr2 <- DDT(st2@traces[[1]],TRUE,TRUE,0.05) tr1 <- DDT(st1@traces[[1]],TRUE,TRUE,0.05) # Bandpass filter trZ_f <- butterworth(trZ,2,0.02,0.04,type='pass') tr2_f <- butterworth(tr2,2,0.02,0.04,type='pass') tr1_f <- butterworth(tr1,2,0.02,0.04,type='pass') # 3 rows layout(matrix(seq(3))) # Plot plot(trZ_f) abline(v=verticalLines,col='gray50',lty=2) plot(tr2_f) abline(v=verticalLines,col='gray50',lty=2) plot(tr1_f) abline(v=verticalLines,col='gray50',lty=2) # Restore default layout layout(1) ## End(Not run) ```

butterworth function