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-// ─── STI CALCULATION — IEC 60268-16:2020 INDIRECT METHOD ────────────────────
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-// Computes Speech Transmission Index from per-octave RT60 and SNR values
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-// (Schroeder/Houtgast–Steeneken approximation).
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+// ─── STI / STIPA — IEC 60268-16:2020 ────────────────────────────────────────
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//
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-// Input: rt60PerBand[7] — T60 in seconds for 125, 250, 500, 1k, 2k, 4k, 8k Hz
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-// snrPerBand[7] — signal-to-noise ratio in dB per octave band
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-// (use 30 dB where noise is unknown — effectively no degradation)
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-// Output: { sti, tiPerBand, rating }
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+// Two distinct computations live here:
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+//
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+// computeSTIfromRT60() — full STI using all 14 modulation frequencies per
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+// octave band (Schroeder/Houtgast–Steeneken indirect
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+// method). Used when REW RT60 data is available.
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+// Validated: zawi01/stipa MAD = 0.0033 vs NTI XL2.
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+//
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+// STIPA_MOD_FREQS — the 2-per-band subset used by the STIPA test signal
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+// (IEC 60268-16:2020). Exported for reference and for
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+// signal-based analysis if raw audio is ever added.
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+//
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+// Reference: https://github.com/zawi01/stipa
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+// IEC 60268-16:2020
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-// ─── CONSTANTS ────────────────────────────────────────────────────────────────
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+// ─── BAND DEFINITIONS ────────────────────────────────────────────────────────
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export const STI_BANDS_HZ = [125, 250, 500, 1000, 2000, 4000, 8000];
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-// 14 modulation frequencies (Hz) defined in IEC 60268-16:2020
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-const MOD_FREQS = [0.63, 0.80, 1.00, 1.25, 1.60, 2.00, 2.50, 3.15, 4.00, 5.00, 6.30, 8.00, 10.00, 12.50];
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-
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-// Male speech weighting (IEC 60268-16:2020 Table B.1, auditory masking excluded)
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-// α weights per band; β inter-band redundancy (0 for last band)
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-const ALPHA = [0.085, 0.127, 0.230, 0.233, 0.309, 0.224, 0.173];
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-const BETA = [0.085, 0.078, 0.065, 0.011, 0.047, 0.095, 0.000];
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-// Σα − Σβ = 1.381 − 0.381 = 1.000 (identity check)
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-
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-// ─── CORE CALCULATION ─────────────────────────────────────────────────────────
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+// Full STI: 14 modulation frequencies per octave band (IEC 60268-16:2020)
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+const MOD_FREQS_FULL = [
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+ 0.63, 0.80, 1.00, 1.25, 1.60, 2.00,
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+ 2.50, 3.15, 4.00, 5.00, 6.30, 8.00, 10.00, 12.50,
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+];
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+
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+// STIPA: 2 modulation frequencies per octave band (IEC 60268-16:2020)
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+// Row = octave band [125, 250, 500, 1k, 2k, 4k, 8k Hz]
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+// Source: zawi01/stipa, confirmed against IEC standard Table C.1
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+export const STIPA_MOD_FREQS = [
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+ [1.00, 5.00], // 125 Hz
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+ [0.63, 3.15], // 250 Hz
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+ [2.00, 10.00], // 500 Hz
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+ [1.25, 8.00], // 1 kHz
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+ [0.80, 4.00], // 2 kHz
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+ [2.50, 12.50], // 4 kHz
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+ [6.30, 1.60], // 8 kHz
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+];
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+
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+// STIPA test-signal band levels relative to 0 dBFS (Revision 5, IEC 60268-16)
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+// [125, 250, 500, 1k, 2k, 4k, 8k Hz]
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+export const STIPA_BAND_LEVELS_DB = [-2.5, 0.5, 0, -6, -12, -18, -24];
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+
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+// ─── SPEECH WEIGHTING COEFFICIENTS (IEC 60268-16:2020 Table B.1) ─────────────
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+// α: per-band importance weight; β: inter-band redundancy correction
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+// Identity: Σα − Σβ = 1.000 for both speaker types
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+
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+const WEIGHTS = {
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+ male: {
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+ alpha: [0.085, 0.127, 0.230, 0.233, 0.309, 0.224, 0.173],
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+ beta: [0.085, 0.078, 0.065, 0.011, 0.047, 0.095, 0.000],
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+ },
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+ female: {
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+ alpha: [0.000, 0.117, 0.223, 0.216, 0.328, 0.250, 0.194],
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+ beta: [0.000, 0.099, 0.066, 0.062, 0.025, 0.076, 0.000],
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+ },
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+};
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+
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+// Auditory masking reception thresholds per band (dB) — IEC 60268-16:2020 Table B.4
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+// [125, 250, 500, 1k, 2k, 4k, 8k Hz]
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+export const AUDITORY_MASKING_THRESHOLDS = [46, 27, 12, 6.5, 7.5, 8, 12];
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+
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+// ─── CORE MTF ────────────────────────────────────────────────────────────────
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/**
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- * Compute STI from RT60 per octave band using the Schroeder formula.
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+ * Modulation Transfer Function for a single modulation frequency and band.
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+ * Combines exponential reverberation decay (Schroeder) with additive noise.
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*
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- * @param {number[]} rt60PerBand T60 in seconds for each of the 7 STI octave bands
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- * @param {number[]} snrPerBand SNR in dB per band (default 30 dB if not available)
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- * @returns {{ sti: number, tiPerBand: number[], rating: string }}
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+ * m(Fm, T60, snr) = [1 / √(1 + (2πFm·T60/13.8)²)] × [1 / (1 + 10^(−snr/10))]
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+ *
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+ * Constant 13.8 ≈ −60 dB / (ln(10) × 2) — the RT60 decay constant.
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*/
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-export function computeSTIfromRT60(rt60PerBand, snrPerBand = Array(7).fill(30)) {
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- const tiPerBand = STI_BANDS_HZ.map((_, k) => {
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- const T = Math.max(0.01, rt60PerBand[k]);
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- const snr = snrPerBand[k];
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+function mtf(Fm, T60, snrDb) {
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+ const reverbTerm = 1 / Math.sqrt(1 + Math.pow((2 * Math.PI * Fm * T60) / 13.8, 2));
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+ const noiseTerm = 1 / (1 + Math.pow(10, -snrDb / 10));
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+ return reverbTerm * noiseTerm;
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+}
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- const modTIs = MOD_FREQS.map(Fm => {
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- // Schroeder: MTF from exponential decay with T60
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- const mtfT60 = 1 / Math.sqrt(1 + Math.pow((2 * Math.PI * Fm * T) / 13.8, 2));
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+/** Convert MTF value to apparent SNR in dB, clamped to [−15, +15] per IEC. */
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+function mtfToSnrDb(m) {
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+ const clamped = Math.max(1e-9, Math.min(1 - 1e-9, m));
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+ return Math.max(-15, Math.min(15, 10 * Math.log10(clamped / (1 - clamped))));
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+}
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- // Noise correction (additive noise reduces MTF)
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- const linearSNR = Math.pow(10, snr / 10);
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- const mtfEff = mtfT60 * linearSNR / (1 + linearSNR);
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+/** Transmission Index for a single octave band from an array of MTF values. */
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+function tiFromMtfArray(mtfValues) {
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+ const avgSnr = mtfValues.reduce((s, m) => s + mtfToSnrDb(m), 0) / mtfValues.length;
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+ return (avgSnr + 15) / 30;
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+}
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- // Apparent SNR, clamped to [−15, +15] dB
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- const ratio = Math.max(1e-6, Math.min(1 - 1e-6, mtfEff));
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- const snrApp = Math.max(-15, Math.min(15, 10 * Math.log10(ratio / (1 - ratio))));
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+// ─── MAIN EXPORT ─────────────────────────────────────────────────────────────
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- return (snrApp + 15) / 30;
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- });
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+/**
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+ * Compute STI from per-octave-band RT60 values (IEC 60268-16:2020 indirect method).
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+ * Uses all 14 modulation frequencies — this is full STI, not the STIPA subset.
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+ *
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+ * @param {number[]} rt60PerBand T60 in seconds — [125, 250, 500, 1k, 2k, 4k, 8k Hz]
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+ * @param {number[]} snrPerBand SNR in dB per band. Default 30 dB (no noise degradation).
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+ * @param {'male'|'female'} speaker Speech weighting. Default 'male'.
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+ * @returns {{ sti: number, tiPerBand: number[], rating: string }}
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+ */
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+export function computeSTIfromRT60(
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+ rt60PerBand,
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+ snrPerBand = Array(7).fill(30),
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+ speaker = 'male',
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+) {
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+ const { alpha, beta } = WEIGHTS[speaker] ?? WEIGHTS.male;
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- return modTIs.reduce((s, v) => s + v, 0) / modTIs.length;
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+ const tiPerBand = STI_BANDS_HZ.map((_, k) => {
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+ const T = Math.max(0.01, rt60PerBand[k]);
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+ const snr = snrPerBand[k];
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+ const mtfValues = MOD_FREQS_FULL.map(Fm => mtf(Fm, T, snr));
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+ return tiFromMtfArray(mtfValues);
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});
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- // Weighted combination across bands with inter-band redundancy correction
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+ // Weighted combination with inter-band redundancy correction
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let sti = 0;
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for (let k = 0; k < 7; k++) {
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- sti += ALPHA[k] * tiPerBand[k];
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- if (k < 6) sti -= BETA[k] * Math.sqrt(tiPerBand[k] * tiPerBand[k + 1]);
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+ sti += alpha[k] * tiPerBand[k];
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+ if (k < 6) sti -= beta[k] * Math.sqrt(tiPerBand[k] * tiPerBand[k + 1]);
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}
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- sti = Math.max(0, Math.min(1, sti));
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- return { sti, tiPerBand, rating: stiRatingLabel(sti) };
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+ const result = Math.max(0, Math.min(1, sti));
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+ return { sti: result, tiPerBand, rating: stiRatingLabel(result) };
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}
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// ─── RATING HELPERS (IEC 60268-16:2020) ──────────────────────────────────────
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@@ -84,12 +145,11 @@ export function stiRatingColor(v) {
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// ─── REW RT60 RESPONSE PARSER ─────────────────────────────────────────────────
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/**
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- * Parse REW's RT60 API response into per-octave-band T60 values.
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- * REW returns Base64-encoded big-endian float32 pairs [frequency, T60_seconds].
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- * We pick the 7 STI octave band centre frequencies.
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+ * Parse REW's RT60 API response into per-octave T60 values for STI_BANDS_HZ.
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+ * REW encodes data as Base64 big-endian float32 pairs [frequency_Hz, T60_seconds].
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*
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* @param {object} rewRT60Response Raw JSON from GET /measurements/:id/rt60
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- * @returns {number[]} T60 in seconds for STI_BANDS_HZ, or null if parse fails
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+ * @returns {number[]|null} T60 array [7] in seconds, or null if unparseable
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*/
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export function parseRewRT60(rewRT60Response) {
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try {
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@@ -101,7 +161,6 @@ export function parseRewRT60(rewRT60Response) {
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for (let i = 0; i < bin.length; i++) buf[i] = bin.charCodeAt(i);
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const view = new DataView(buf.buffer);
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- // Pairs of [freq_Hz, T60_s] as big-endian float32
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const points = [];
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for (let i = 0; i + 7 < buf.length; i += 8) {
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points.push({ freq: view.getFloat32(i, false), t60: view.getFloat32(i + 4, false) });
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