IIR vs FIR Filters: Key Differences & When to Use Each
IIR (Infinite Impulse Response) filters recycle past outputs, giving infinite tails. FIR (Finite Impulse Response) filters use only past and present inputs, creating finite, predictable responses.
Podcast producers reach for “FIR” presets when they want crisp, linear-phase vocals, while musicians grab “IIR” emulations for vintage warmth. The acronyms sound alike, so newcomers assume both are plug-and-play; in reality, choosing the wrong one can turn a bassline boomy or a podcast hollow.
Key Differences
IIR filters need fewer coefficients, so they run fast on microcontrollers but risk instability and nonlinear phase. FIR filters demand more memory and processing yet guarantee linear phase and rock-solid stability.
Which One Should You Choose?
Pick IIR for battery-powered wearables or vintage synth plugins where CPU and nostalgia matter. Choose FIR for medical imaging, wireless communications, or any system where phase distortion could garble data.
Can IIR filters ever be linear-phase?
No; feedback paths inherently introduce phase distortion. You can approximate, but true linear phase is FIR-only territory.
Are FIR filters always slower than IIR?
Not with modern FFT-based convolution; large-block processing can make FIR faster than recursive IIR in high-end DSP chips.
Why do guitar amp sims use IIR?
They mimic analog circuits that naturally have feedback; IIR captures that nonlinear warmth with fewer calculations.