iir: Apply IIR filter to the signal

In MIMSunit: Algorithm to Compute Monitor Independent Movement Summary Unit (MIMS-Unit)

Apply IIR filter to the signal

Description

iir function takes a multi-channel signal and applies an IIR filter to the signal.

Usage

iir(df, sr, cutoff_freq, order = 4, type = "high", filter_type = "butter")

Arguments

df	dataframe. The input multi-channel signal. The first column is timestamps in POSXlct format. The rest columns are signal values.
sr	number. Sampling rate in Hz of the input signal.
cutoff_freq	number or numerical vector. The cutoff frequencies in Hz. If the IIR filter is a bandpass or bandstop filter, it will be a 2-element numerical vector specifying the low and high end cutoff frequencies c(low, high).
order	number. The order of the filter. Default is 4.
type	string. Filtering type, one of "low" for a low-pass filter, "high" for a high-pass filter, "stop" for a stop-band (band-reject) filter, or "pass" for a pass-band filter.
filter_type	string. IIR filter type, one of "butter" for butterworth filter, "chebyI" for Chebyshev Type I filter, or "ellip" for Elliptic filter.

Details

This function filters the input multi-channel signal by applying an IIR filter. See wiki for the explanation of the filter. The implementations of IIR filters can be found in butter, cheby1, and ellip.

For Chebyshev Type I, Type II and Elliptic filter, the passband ripple is fixed to be 0.05 dB. For Elliptic filter, the stopband ripple is fixed to be -50dB.

Value

dataframe. Filtered signal.

How is it used in MIMS-unit algorithm?

This function has been used as the main filtering method in MIMS-unit algorithm. Specifically, it uses a 0.5 - 5 Hz bandpass butterworth filter during filtering.

See Also

Other filtering functions: bandlimited_interp()

Examples

  # Use sample data
  df = sample_raw_accel_data

  # View input
  illustrate_signal(df, plot_maxed_out_line = FALSE)

  # Apply filtering that uses the same setting as in MIMSunit algorithm
  output = iir(df, sr=80, cutoff_freq=c(0.2, 5), type='pass')

  # View output
  illustrate_signal(output, plot_maxed_out_line = FALSE)

MIMSunit documentation built on June 21, 2022, 5:06 p.m.