decimate {signal}

Decimate or downsample a signal

Description

Downsample a signal by a factor, using an FIR or IIR filter.

Usage

decimate(x, q, n = if (ftype == "iir") 8 else 30, ftype = "iir")

Arguments

x

signal to be decimated.

q

integer factor to downsample by.

n

filter order used in the downsampling.

ftype

filter type, "iir" or "fir"

Details

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.

Value

The decimated signal, an array of length ceiling(length(x) / q).

Author(s)

Original Octave version by Paul Kienzle [e-mail]. Conversion to R by Tom Short.

References

Octave Forge https://octave.sourceforge.io/

See Also

filter, resample, interp

Examples

# 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")