Reduce the sampling rate

This function is used to reduce the sampling rate of a time series by an integer factor.

Usage

decdc(x, df)

Arguments

x

A data structure, vector or matrix containing the signal(s) to be decimated. If x is a matrix, each column is decimated separately.

df

The decimation factor. The output sampling rate is the input sampling rate divided by df. df must be an integer greater than 1.

Value

y The decimated signal vector or matrix. It has the same number of columns as x but has 1/df of the rows.

Note

Decimation is performed by first low-pass filtering x and then keeping 1 sample out of every df. A symmetric FIR filter with length 12*df and cutoff frequency 0.4*fs/df is used. The group delay of the filter is removed. For large decimation factors (e.g., df>>50), it is better to perform several decimations with lower factors. For example to decimate by 120, use: decdc(decdc(x,10),12).

Examples

s <- matrix(sin(2 * pi / 100 * c(0:1000) - 1), ncol = 1)
plot(c(1:length(s)), s) 

y <- decdc(x = s, df = 4)
plot(c(1:length(y)), y)