# 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.

## See Also:

DECILP

DECIMATE

REMOVE

RESAMPLE

UPSAMPLE