Decimate or downsample a signal
Downsample a signal by a factor, using an FIR or IIR filter.
decimate(x, q, n = if (ftype == "iir") 8 else 30, ftype = "iir")
x |
signal to be decimated. |
q |
integer factor to downsample by. |
n |
filter order used in the downsampling. |
ftype |
filter type, |
By default, an order 8 Chebyshev type I
filter is used or a 30-point FIR filter if ftype is 'fir'. Note
that q must be an integer for this rate change method.
Makes use of the filtfilt function with all its limitations.
The decimated signal, an array of length ceiling(length(x) / q).
Original Octave version by Paul Kienzle pkienzle@user.sf.net. Conversion to R by Tom Short.
Octave Forge http://octave.sf.net
# The signal to decimate starts away from zero, is slowly varying # at the start and quickly varying at the end, decimate and plot. # Since it starts away from zero, you will see the boundary # effects of the antialiasing filter clearly. You will also see # how it follows the curve nicely in the slowly varying early # part of the signal, but averages the curve in the quickly # varying late part of the signal. t <- seq(0, 2, by = 0.01) x <- chirp(t, 2, 0.5, 10, 'quadratic') + sin(2*pi*t*0.4) y <- decimate(x, 4) # factor of 4 decimation plot(t, x, type = "l") lines(t[seq(1,length(t), by = 4)], y, col = "blue")
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