Notch filter (power line noise removal)

Applies a notch filter to remove power line noise (50 Hz or 60 Hz) and optionally its harmonics. Implemented as a Butterworth bandstop filter with zero-phase filtering.

Usage

notchFilter(
  x,
  freq = 50,
  bandwidth = 2,
  harmonics = 1L,
  output_assay = "filtered"
)

Arguments

x

A PhysioExperiment object.

freq

Center frequency to remove in Hz. Default is 50 (European power line).

bandwidth

Bandwidth of the notch in Hz. Default is 2.

harmonics

Number of harmonics to remove. Default is 1 (only fundamental).

output_assay

Name for the output assay. Default is "filtered".

Value

A PhysioExperiment object with a new assay named output_assay containing the notch-filtered data. Harmonics above the Nyquist frequency are skipped with a warning.

References

Oppenheim, A.V. & Willsky, A.S. (1997). "Signals and Systems." 2nd ed. Prentice Hall.

See also

butterworthFilter() for general Butterworth filtering, firFilter() for FIR filtering, filterSignals() for moving average filtering.

Examples

pe <- PhysioExperiment(
  assays = list(raw = matrix(rnorm(1000 * 4), nrow = 1000)),
  samplingRate = 250
)

# Remove 50 Hz power line noise (Europe/Asia)
pe <- notchFilter(pe, freq = 50)

# Remove 60 Hz and harmonics (Americas)
pe <- notchFilter(pe, freq = 60, harmonics = 2)