REW Excess Phase FIR · v2

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Local excess-phase analysis and near-allpass FIR design for REW measurements. Supports stereo, unknown and multiway crossovers, paired surround channels, independent channels, and aligned subwoofer systems. Author: Winter-Ignition.

After enabling the FIR, remeasure and recalibrate frequency-response EQ, including any EQ already in use. Preserve essential crossovers, protection and physical alignment delays. Disable the mixed-phase or excess-phase correction being replaced when making a fresh baseline measurement.

Features

• Extracts excess phase from native impulse responses or dense magnitude/total-phase exports. Defaults to 1/6-octave complex-vector smoothing, with wrap and window sensitivity checks.
• Separates the speaker’s lowest undistorted frequency from the measurement’s noise-dominated lower boundary. Fits an equivalent low-end magnitude extension without using observations below that boundary; records alternative-model sensitivity.
• Solves broad phase correction across the usable lower bound to 10 kHz. Faster local group-delay detail is restricted to the lower of 300 Hz and a head-movement estimate; this local limit does not restrict broad correction.
• Fits channels independently. Smoothly joins the common correction above 10 kHz and reduces paired-channel differences near 10 kHz, without forcing all higher-frequency excess phase to zero. Exit frequencies follow available trusted bandwidth.
• Can revise measurements made with a previous FIR. Requires the actual loaded coefficients, hash, channel mapping and common delay; exports one complete replacement rather than another layer.
• Defaults to 192 kHz, 16384 taps, float32 WAV and 42.67 ms common reference delay. Reads exported coefficients back for gain, advance-energy, transition, composition and symmetry checks, including direct DTFT cross-checks.
• Generates offline HTML, PNG, CSV, a channel manifest and coefficient acceptance results. Acoustic remeasurement uses the original low-end reference and smoothing convention.

Measurement example

Real listening-position measurements from one stereo system, with 1/6-octave vector smoothing and analysis-only timing reference removal. The gray dashed curves come from the retained initial measurement analysis; the blue curves are the final acoustic remeasurement, not a prediction. The lower panel enlarges the remaining phase variation.

The low-frequency reference was refined during the work, so the plot below shows the final remeasurement on its own. It uses a fitted low-end reference; dotted segments indicate lower vector coherence. Room-related structure and measurement noise remain visible.