# Finite Impulse Response filter This function is a FIR filter that filters out a selected frequency section of a time wave (low-pass, high-pass, low-stop, high-stop, bandpass or bandstop frequency filter). ```r fir(wave, f, channel = 1, from = NULL, to = NULL, bandpass = TRUE, custom = NULL, wl = 512, wn = "hanning", rescale=FALSE, 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). - `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`). - `custom`: a vector describing the frequency response of a custom filter. This can be manually generated or obtained with `spec` and `meanspec`. `wl` is no more required. See examples. - `wl`: window length of the impulse filter (even number of points). - `wn`: window name, see `ftwindow` (by default `"hanning"`). - `rescale`: a logical, if `TRUE` then the sample values of new wave (output) are rescaled according to the sample values of `wave` (input). - `listen`: a logical, 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 This function is based on the reverse of the Fourier Transform (`fft`) and on a convolution (`convolve`) between the wave to be filtered and the impulse filter. ## Returns A new wave is returned. The class of the returned object is set with the argument `output`. ## 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. ## Author(s) Jerome Sueur ## See Also `ffilter`, `bwfilter`, `preemphasis`, `lfs`, `afilter` ## Examples ```r a<-noisew(f=8000,d=1) # low-pass b<-fir(a,f=8000,to=1500) spectro(b,f=8000) # high-pass c<-fir(a,f=8000,from=2500) spectro(c,f=8000) # band-pass d<-fir(a,f=8000,from=1000,to=2000) spectro(d,f=8000) # band-stop e<-fir(a,f=8000,from=1500,to=2500,bandpass=FALSE) spectro(e,f=8000) # custom filter manually generated myfilter1<-rep(c(rep(0,32),rep(1,32)),4) g<-fir(a,f=8000,custom=myfilter1) spectro(g,f=8000) # custom filter generated using spec() data(tico) myfilter2<-spec(tico,f=22050,at=0.7,wl=512,plot=FALSE) b<-noisew(d=1,f=22050) h<-fir(b,f=22050,custom=myfilter2) spectro(h,f=22050) ```

fir function