Field Guide · algorithm

Also known as: FIR, finite impulse response filter

A FIR (finite impulse response) filter produces each output sample as a weighted sum of the most recent input samples — a tapped delay line multiplied by a set of coefficients (taps).1 It is the most common digital filter in SDR because it is always stable and can have exactly linear phase.

z⁻¹z⁻¹z⁻¹z⁻¹ ×a₀×a₁×a₂×a₃ Σ out
A FIR filter delays the input, scales each tap by a coefficient, and sums them — a direct convolution.

Overview

FIR filters are used for channel selection, pulse shaping, and as the anti-alias filter before decimation. Their coefficients directly define the frequency response.

Sources

  1. Finite impulse response — Wikipedia, on the non-recursive, always-stable filter and its linear phase. ↩

See also

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