Downsampling

Summary

Doc_BoxAlgorithm_Downsampling.png
  • Plugin name : Downsampling
  • Version : 1.01
  • Author : G. Gibert - E. Maby - P.E. Aguera
  • Company : INSERM/U821
  • Short description : Filters and downsamples input buffer.
  • Documentation template generation date : Nov 2 2017

Description

First, applies a low-pass (Butterworth or Chebychev) filter (frequency cut is 1/4, 1/3 or 1/2 of the new sampling rate) to input buffers of signal for anti-aliasing. Then, the input buffers of signal is downsampled.

This plugin is used to downsample the input signal. First, a low-pass filter is applied to the input signal for anti-aliasing. Then, the input signal is downsampled at the new sampling rate. This plugin allows the selection of the kind of filter (Butterworth or Chebychev), the new sampling rate and the frequency cutoff for the filter.

Inputs

1. Input signal

The input signal.

  • Type identifier : Signal (0x5ba36127, 0x195feae1)

Outputs

1. Output signal

  • Type identifier : Signal (0x5ba36127, 0x195feae1)

Settings

1. New sampling rate (Hz)

New sampling rate in Hz chosen to downsample the input signal.

  • Type identifier : Integer (0x007deef9, 0x2f3e95c6)
  • Default value : [ 32 ]

2. Frequency cutoff ratio

Select the frequency cutoff of the low-pass filter as a ratio (1/2, 1/3 or 1/4) of the new sampling rate.

  • Type identifier : Frequency cut off ratio (0x709fc9df, 0x30a2cb2a)
  • Default value : [ 1/4 ]

3. Name of filter

Select the kind of filter between Butterworth and Chebychev.

  • Type identifier : Filter method (0x2f2c606c, 0x8512ed68)
  • Default value : [ Butterworth ]

4. Filter order

Order of the low-pass filter.

  • Type identifier : Integer (0x007deef9, 0x2f3e95c6)
  • Default value : [ 4 ]

5. Pass band ripple (dB)

If Chebychev filter is selected, PassBand Ripple is a necessary info.

  • Type identifier : Float (0x512a166f, 0x5c3ef83f)
  • Default value : [ 0.5 ]

Examples

Let's consider our input signal sampling rate is 1 kHz. If the new selected sampling rate is 200 Hz and the Frequency cutoff ratio is 1/4, then a low-pass filter (with frequency cutoff equal to 200*1/4 = 50 Hz) is applied before downsampling at 200 Hz.

Miscellaneous

This plugin downsamples the input signal and previously realizes an anti-aliasing filtering.