# DOWNSAMPLE

## Purpose:

Deletes every Nth sample for FIR downsampling.

## Syntax:

DOWNSAMPLE(series, n, offset)

 series - Any series, multi-series table, or expression resulting in a series or table. n - An integer factor by which to decimate the series. Deletes N-1 samples between each sample, decreasing the sample rate by a factor of N. Defaults to 1, no rate change. offset - Optional. An integer, the starting offset for the decimation. Defaults to 0, start decimation after the first sample.

## Returns:

A series, the decimated series.

## Example:

W1: 1..5

W2: downsample(W1, 2)

W2 == {1, 3, 5}

rate(w1) == 1

rate(w2) == 0.5

Reduces the series in W1 by a factor of 2 by keeping every other point.

## Example:

W3: 1..5

W4: downsample(W3, 3)

W4 == {1, 4}

rate(w3) == 1

rate(w4) == 1/3

Reduces the series in W3 by a factor of 3 by keeping every third point.

## Example:

W1: 1..5

W2: downsample(W1, 3, 1)

W2 == {2, 5}

rate(w3) == 1

rate(w4) == 1/3

Reduces the series in Window 1 by a factor of 3 by keeping every third point starting at the second point.

## Remarks:

DOWNSAMPLE decreases the sample RATE of the input series by a factor of N by removing N-1 samples between each sample.

A downsampled series can be decimated by filtering the result with a low pass filter with a cut off frequency of (Fs/2) / N where Fs is the original sample rate. The band limited frequency content of the original series is preserved.

The decimation factor automatically adjusts the sample rate (1/DELTAX) of the resulting series.

See DECILP to perform band limited decimation by means of low pass filtering.

DECILP

DECIMATE

REMOVE

RESAMPLE

UPSAMPLE