FIR filter

Applies a Finite Impulse Response (FIR) filter along the time axis. Uses zero-phase forward-backward filtering via signal::filtfilt() to avoid phase distortion.

Usage

firFilter(
  x,
  low = NULL,
  high = NULL,
  order = 100L,
  type = c("pass", "low", "high", "stop"),
  window = "hamming",
  causal = FALSE,
  output_assay = "filtered"
)

Arguments

x

A PhysioExperiment object.

low

Lower cutoff frequency in Hz.

high

Upper cutoff frequency in Hz.

order

Filter order (number of taps - 1). Default is 100.

type

Filter type: "low", "high", "pass" (bandpass), or "stop" (bandstop).

window

Window function for FIR design. Default is "hamming".

causal

Logical. If FALSE (default), apply zero-phase forward-backward filtering (signal::filtfilt()), which is non-causal. If TRUE, apply a single forward (causal) pass via lfilter() with a steady-state warm start, producing a real-time-equivalent result (linear-phase group delay of order / 2 samples, no acausal pre-ringing).

output_assay

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

Value

A PhysioExperiment object with a new assay named output_assay containing the FIR-filtered data. Dimensions match the input assay.

References

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

See also

butterworthFilter() for IIR filtering, notchFilter() for power line noise removal, filterSignals() for moving average filtering, lfilter() for the underlying causal filtering primitive.