LinFIR

Filter design for loudspeakers and rooms

LinFIR is the software I develop to design filters, and it also simulates what your DSP will really do with them. You design linear-phase or minimum-phase FIR filters, IIR crossovers and EQ, and LinFIR applies them to your actual measurements. Magnitude, phase, impulse, step and group delay update in real time as you work.

There are two modes. Loudspeaker Design covers multi-way crossovers, driver correction, time alignment and directivity. Room Calibration handles in-room measurements at several positions, and the correction that goes with them. The interface is available in English and French.

LinFIR is free for on-axis work, with every design and export feature included. The Advanced Module adds off-axis, directivity and spinorama analysis, and is a one-time purchase.

Read the documentation.

Download LinFIR

LinFIR main window: driver and system responses, impulse response, step response and group delay

What LinFIR Does Best

Crossovers with Real-Time Feedback

Linear-phase Linkwitz-Riley, Butterworth, Bessel and brickwall FIR filters (32 to 65,536 taps), with causality adjustable from linear to minimum phase, alongside IIR crossovers. Every change is shown instantly on your drivers’ measured responses.

Driver and System Correction

FIR magnitude and phase correction to flat, Harman or custom target curves, and IIR Auto EQ. Correct against the on-axis, the Listening Window or the Predicted In-Room response, per driver or for the whole system.

Time Alignment

Skip the “measure, adjust, remeasure” loop. Adjust delay and gain per driver and instantly see how the combined response changes across the crossover regions.

CTA-2034-A Spinorama

Listening Window, Early Reflections, Sound Power, Predicted In-Room Response and both Directivity Indices, computed per the ANSI/CTA-2034-A standard from your own polar measurements, with your filters applied.

Built-In Measurements

Exponential sine sweeps with harmonic distortion separation, microphone calibration files, driver-protection high-pass, and rotation table control (GRBL and Pololu Tic) for automated polar measurements.

Near-Field / Far-Field Splicing

A step-by-step wizard that builds a full-range anechoic response from near-field captures and far-field polar measurements, including baffle diffraction, level matching and blending.

Core Features

Two Modes

Loudspeaker Design and Room Calibration, each with its own workflow

FIR Filters

32 to 65,536 taps, linear to minimum phase, Kaiser window shaping

IIR Filters

PEQ, shelves, all-pass and crossovers, with Auto EQ

Target Curves

Flat, Harman in-room or your own custom targets

Measurements

Sweeps, mic calibration, multi-position averaging with automatic alignment

Visualization

Magnitude, phase, group delay, impulse, step and THD graphs, detachable windows

DSP Exports

CamillaDSP, MiniDSP, Q-SYS, Hypex FusionAmp, Powersoft Armonía and more

Cross-Platform

Mac and Windows, interface in English or French, projects compatible across both

The Advanced Module

Everything LinFIR does on-axis is free. If you work with off-axis measurements and directivity, you need the Advanced Module. €149, tax included, one-time purchase.

Off-axis measurements, horizontal and vertical, with multi-angle views
Directivity analysis: sonogram, overlay plots and Directivity Index
Full CTA-2034-A spinorama: Listening Window, Early Reflections, Sound Power, Predicted In-Room
Off-axis prediction through the real signal chain, FIR and IIR included
Spectrogram, cumulative spectral decay and 3D waterfall
Harmonic distortion breakdown and distortion impulse responses
Near-field / far-field splicing wizard
Auto EQ auto-generate and pre-filter response overlays
Free updates for all 1.x versions, no subscription
One activation at a time, movable between your computers

Buy a license (€149)

Download LinFIR

Mac OS Silicon

.dmg

Windows x64

via Windows store

Why Linear-Phase FIR Filters?

I use linear-phase FIR crossovers in the loudspeakers I design, and IIR filters where their minimum-phase behaviour actually helps.

Blind listening tests have not shown a clear audible advantage for a linear-phase loudspeaker on its own, and phase distortion has to be severe before anyone hears it. The real benefit is at the crossover. When the drivers stay in phase through the crossover region, they sum as intended, and there is no need to boost a band to make up for a partial cancellation.

The room is another matter. The way it interacts with the speaker is very complex and still poorly understood, and starting from a linear-phase speaker makes the problem a little simpler. There is also an engineer's satisfaction in doing things cleanly. Since it can be done, why not do it?

Crossovers Without Phase Rotation

A linear-phase crossover sums drivers without the phase rotation and group delay of classic IIR or passive crossovers, so the impulse and step response stay coherent.

Correction That Includes Phase

FIR filters can correct magnitude and phase independently: flatten driver irregularities and excess group delay, or match a target curve, with limits and smoothing so the correction stays sensible.

Creative Multi-Driver Configurations

Blend drivers with linear-phase versions of Linkwitz-Riley, Butterworth, and Bessel filters. Need asymmetric slopes? No problem. Want to apply a gentle low-pass to one woofer in a D’Appolito configuration? Easy.
Use this to:
• Compensate rising frequency response from high-efficiency drivers
• Tweak baffle step compensation
• Improve directivity by reducing frequency overlap

Directivity and the room

What you hear in a room is a mix of direct and reflected sound. That's why I design against the Directivity Index and the Predicted In-Room Response as well as the on-axis curve. Those curves say much more about how a speaker will sound in a real room.

Minimum Phase When It Matters

LinFIR includes a minimum-phase conversion based on homomorphic filtering (Oppenheim et al., Signal Analysis by Homomorphic Prediction, IEEE TASSP, 1976), and a continuous causality control between linear and minimum phase.
This keeps the magnitude response intact while minimizing latency. It's useful for live sound, low-latency correction and hybrid designs.