feat: add APO export for legacy EQ and fix shelf filter Q support

- Add Export APO button to legacy graphic EQ (GraphicEQ config line format)
- Fix shelf filters ignoring Q: use IIR filters with RBJ cookbook coefficients
- Update graph visualization to use actual Q for shelf curves
- Omit Q from shelf filters in all EQ text exports

index.html

@@ -4381,6 +4381,13 @@
                                             >
                                                 Export
                                             </button>
+                                            <button
+                                                id="legacy-geq-export-csv-btn"
+                                                class="btn-secondary"
+                                                title="Export EQ as Equalizer APO GraphicEQ config line"
+                                            >
+                                                Export APO
+                                            </button>
                                             <input
                                                 type="file"
                                                 id="legacy-geq-import-file"

js/audio-context.js

@@ -5,6 +5,41 @@
 import { isIos } from './platform-detection.js';
 import { equalizerSettings, monoAudioSettings } from './storage.js';
 
+/**
+ * Compute RBJ cookbook IIR coefficients for shelf filters with Q support.
+ * Web Audio API's BiquadFilterNode ignores Q for lowshelf/highshelf,
+ * so we use IIRFilterNode with these coefficients instead.
+ */
+function computeShelfCoefficients(type, freq, gainDb, q, sampleRate) {
+    const A = Math.pow(10, gainDb / 40);
+    const w0 = (2 * Math.PI * freq) / sampleRate;
+    const alpha = Math.sin(w0) / (2 * q);
+    const cosW0 = Math.cos(w0);
+    const sqA = 2 * Math.sqrt(A) * alpha;
+    let b0, b1, b2, a0, a1, a2;
+
+    if (type === 'lowshelf') {
+        b0 = A * (A + 1 - (A - 1) * cosW0 + sqA);
+        b1 = 2 * A * (A - 1 - (A + 1) * cosW0);
+        b2 = A * (A + 1 - (A - 1) * cosW0 - sqA);
+        a0 = A + 1 + (A - 1) * cosW0 + sqA;
+        a1 = -2 * (A - 1 + (A + 1) * cosW0);
+        a2 = A + 1 + (A - 1) * cosW0 - sqA;
+    } else {
+        b0 = A * (A + 1 + (A - 1) * cosW0 + sqA);
+        b1 = -2 * A * (A - 1 + (A + 1) * cosW0);
+        b2 = A * (A + 1 + (A - 1) * cosW0 - sqA);
+        a0 = A + 1 - (A - 1) * cosW0 + sqA;
+        a1 = 2 * (A - 1 - (A + 1) * cosW0);
+        a2 = A + 1 - (A - 1) * cosW0 - sqA;
+    }
+
+    return {
+        feedforward: [b0 / a0, b1 / a0, b2 / a0],
+        feedback: [1, a1 / a0, a2 / a0],
+    };
+}
+
 // Generate frequency array for given number of bands using logarithmic spacing
 function generateFrequencies(bandCount, minFreq = 20, maxFreq = 20000) {
     const frequencies = [];
@@ -245,14 +280,24 @@ class AudioContextManager {
         const gainValue = Math.pow(10, preampValue / 20);
         this.preampNode.gain.value = gainValue;
 
-        // Create biquad filters for each frequency band
+        // Create filters for each frequency band
         this.filters = this.frequencies.map((freq, index) => {
+            const type = (this.currentTypes && this.currentTypes[index]) || 'peaking';
+            const q = this.currentQs && this.currentQs[index] > 0 ? this.currentQs[index] : this._calculateQ(index);
+            const gain = this.currentGains[index] || 0;
+
+            if (type === 'lowshelf' || type === 'highshelf') {
+                const coeffs = computeShelfCoefficients(type, freq, gain, q, this.audioContext.sampleRate);
+                const iir = this.audioContext.createIIRFilter(coeffs.feedforward, coeffs.feedback);
+                iir._shelfType = type;
+                return iir;
+            }
+
             const filter = this.audioContext.createBiquadFilter();
-            filter.type = (this.currentTypes && this.currentTypes[index]) || 'peaking';
+            filter.type = type;
             filter.frequency.value = freq;
-            filter.Q.value =
+            filter.Q.value = q;
-                this.currentQs && this.currentQs[index] > 0 ? this.currentQs[index] : this._calculateQ(index);
+            filter.gain.value = gain;
-            filter.gain.value = this.currentGains[index] || 0;
             return filter;
         });
 
@@ -843,12 +888,41 @@ class AudioContextManager {
             // If filter count matches, update params in-place (no graph rebuild)
             if (this.filters.length === count) {
                 const now = this.audioContext.currentTime;
+                let needsReconnect = false;
                 this.filters.forEach((filter, i) => {
-                    filter.type = newTypes[i] || 'peaking';
+                    const type = newTypes[i] || 'peaking';
-                    filter.frequency.setTargetAtTime(newFrequencies[i], now, 0.005);
+                    const q = newQs[i] > 0 ? newQs[i] : this._calculateQ(i);
-                    filter.gain.setTargetAtTime(newGains[i], now, 0.005);
+                    const isShelf = type === 'lowshelf' || type === 'highshelf';
-                    filter.Q.setTargetAtTime(newQs[i] > 0 ? newQs[i] : this._calculateQ(i), now, 0.005);
+                    const wasShelf = !!filter._shelfType;
+
+                    if (isShelf) {
+                        // IIR filters can't update params — must replace the node
+                        const coeffs = computeShelfCoefficients(type, newFrequencies[i], newGains[i], q, this.audioContext.sampleRate);
+                        const iir = this.audioContext.createIIRFilter(coeffs.feedforward, coeffs.feedback);
+                        iir._shelfType = type;
+                        try { filter.disconnect(); } catch { /* ignore */ }
+                        this.filters[i] = iir;
+                        needsReconnect = true;
+                    } else if (wasShelf) {
+                        // Was shelf IIR, now peaking — create new BiquadFilterNode
+                        const biquad = this.audioContext.createBiquadFilter();
+                        biquad.type = type;
+                        biquad.frequency.value = newFrequencies[i];
+                        biquad.gain.value = newGains[i];
+                        biquad.Q.value = q;
+                        try { filter.disconnect(); } catch { /* ignore */ }
+                        this.filters[i] = biquad;
+                        needsReconnect = true;
+                    } else {
+                        filter.type = type;
+                        filter.frequency.setTargetAtTime(newFrequencies[i], now, 0.005);
+                        filter.gain.setTargetAtTime(newGains[i], now, 0.005);
+                        filter.Q.setTargetAtTime(q, now, 0.005);
+                    }
                 });
+                if (needsReconnect) {
+                    this._connectGraph();
+                }
             } else {
                 // Band count changed — must rebuild
                 this._destroyEQ();
@@ -872,10 +946,16 @@ class AudioContextManager {
         const lines = [`Preamp: ${this.preamp.toFixed(1)} dB`];
         sortedBands.forEach((band, index) => {
             if (index >= count) return;
-            const filterType = band.type === 'lowshelf' ? 'LS' : band.type === 'highshelf' ? 'HS' : 'PK';
+            const filterType = band.type === 'lowshelf' ? 'LSC' : band.type === 'highshelf' ? 'HSC' : 'PK';
-            lines.push(
+            if (band.type === 'lowshelf' || band.type === 'highshelf') {
-                `Filter ${index + 1}: ON ${filterType} Fc ${newFrequencies[index]} Hz Gain ${newGains[index].toFixed(1)} dB Q ${newQs[index].toFixed(2)}`
+                lines.push(
-            );
+                    `Filter ${index + 1}: ON ${filterType} Fc ${newFrequencies[index]} Hz Gain ${newGains[index].toFixed(1)} dB`
+                );
+            } else {
+                lines.push(
+                    `Filter ${index + 1}: ON ${filterType} Fc ${newFrequencies[index]} Hz Gain ${newGains[index].toFixed(1)} dB Q ${newQs[index].toFixed(2)}`
+                );
+            }
         });
 
         return lines.join('\n');
@@ -893,12 +973,18 @@ class AudioContextManager {
         this.frequencies.forEach((freq, index) => {
             const gain = this.currentGains[index] || 0;
             const type = (this.currentTypes && this.currentTypes[index]) || 'peaking';
-            const filterType = type === 'lowshelf' ? 'LS' : type === 'highshelf' ? 'HS' : 'PK';
+            const filterType = type === 'lowshelf' ? 'LSC' : type === 'highshelf' ? 'HSC' : 'PK';
-            const q = this.currentQs && this.currentQs[index] > 0 ? this.currentQs[index] : this._calculateQ(index);
             const filterNum = index + 1;
-            lines.push(
+            if (type === 'lowshelf' || type === 'highshelf') {
-                `Filter ${filterNum}: ON ${filterType} Fc ${freq} Hz Gain ${gain.toFixed(1)} dB Q ${q.toFixed(2)}`
+                lines.push(
-            );
+                    `Filter ${filterNum}: ON ${filterType} Fc ${freq} Hz Gain ${gain.toFixed(1)} dB`
+                );
+            } else {
+                const q = this.currentQs && this.currentQs[index] > 0 ? this.currentQs[index] : this._calculateQ(index);
+                lines.push(
+                    `Filter ${filterNum}: ON ${filterType} Fc ${freq} Hz Gain ${gain.toFixed(1)} dB Q ${q.toFixed(2)}`
+                );
+            }
         });
 
         return lines.join('\n');

js/autoeq-engine.js

@@ -24,8 +24,7 @@ function calculateBiquadResponse(f, band, sr = DEFAULT_SR) {
     const w = (2 * PI * band.freq) / sr;
     const p = (2 * PI * f) / sr;
     const t = band.type[0];
-    // WebAudio ignores Q for shelf filters; use 1/√2 (slope = 1) to match
+    const effectiveQ = band.q;
-    const effectiveQ = t === 'l' || t === 'h' ? Math.SQRT1_2 : band.q;
     const s = Math.sin(w) / (2 * effectiveQ);
     const A = Math.pow(DB_BASE, band.gain / DB_DIVISOR);
     const c = Math.cos(w);

js/equalizer.js

@@ -621,9 +621,17 @@ export class Equalizer {
 
         this.frequencies.forEach((freq, index) => {
             const gain = this.currentGains[index] || 0;
-            const q = this.filters[index] ? this.filters[index].Q.value : this._calculateQ(index);
+            const filter = this.filters[index];
+            const type = filter ? filter.type : 'peaking';
+            const typeMap = { peaking: 'PK', lowshelf: 'LSC', highshelf: 'HSC' };
+            const typeStr = typeMap[type] || 'PK';
             const filterNum = index + 1;
-            lines.push(`Filter ${filterNum}: ON PK Fc ${freq} Hz Gain ${gain.toFixed(1)} dB Q ${q.toFixed(2)}`);
+            if (type === 'lowshelf' || type === 'highshelf') {
+                lines.push(`Filter ${filterNum}: ON ${typeStr} Fc ${freq} Hz Gain ${gain.toFixed(1)} dB`);
+            } else {
+                const q = filter ? filter.Q.value : this._calculateQ(index);
+                lines.push(`Filter ${filterNum}: ON ${typeStr} Fc ${freq} Hz Gain ${gain.toFixed(1)} dB Q ${q.toFixed(2)}`);
+            }
         });
 
         return lines.join('\n');

js/settings.js

@@ -1385,14 +1385,19 @@ export async function initializeSettings(scrobbler, player, api, ui) {
 
     // Legacy EQ Import / Export
     const parseGeqLabelFrequency = (label) => {
-        const normalized = String(label).trim().toLowerCase().replace(/hz$/, '').trim();
+        const normalized = String(label).trim().toLowerCase().replace(/\s+/g, '');
-        if (normalized.endsWith('k')) {
+        if (normalized.endsWith('khz')) {
-            return Number.parseFloat(normalized.slice(0, -1)) * 1000;
+            return Number.parseFloat(normalized.slice(0, -3)) * 1000;
         }
-        return Number.parseFloat(normalized);
+        const withoutHz = normalized.replace(/hz$/, '');
+        if (withoutHz.endsWith('k')) {
+            return Number.parseFloat(withoutHz.slice(0, -1)) * 1000;
+        }
+        return Number.parseFloat(withoutHz);
     };
     const GEQ_FREQUENCIES = GEQ_LABELS.map((label) => parseGeqLabelFrequency(label));
     const legacyGeqExportBtn = document.getElementById('legacy-geq-export-btn');
+    const legacyGeqExportCsvBtn = document.getElementById('legacy-geq-export-csv-btn');
     const legacyGeqImportBtn = document.getElementById('legacy-geq-import-btn');
     const legacyGeqImportFile = document.getElementById('legacy-geq-import-file');
 
@@ -1408,7 +1413,21 @@ export async function initializeSettings(scrobbler, player, api, ui) {
             a.href = url;
             a.download = 'legacy-eq.txt';
             a.click();
-            URL.revokeObjectURL(url);
+            setTimeout(() => URL.revokeObjectURL(url), 0);
+        });
+    }
+
+    if (legacyGeqExportCsvBtn) {
+        legacyGeqExportCsvBtn.addEventListener('click', () => {
+            const pairs = GEQ_FREQUENCIES.map((freq, i) => `${freq} ${geqGains[i].toFixed(1)}`).join('; ');
+            const lines = [`Preamp: ${geqPreamp.toFixed(1)} dB`, `GraphicEQ: ${pairs}`];
+            const blob = new Blob([lines.join('\n')], { type: 'text/plain' });
+            const url = URL.createObjectURL(blob);
+            const a = document.createElement('a');
+            a.href = url;
+            a.download = 'legacy-eq-apo.txt';
+            a.click();
+            setTimeout(() => URL.revokeObjectURL(url), 0);
         });
     }
 
@@ -1445,11 +1464,11 @@ export async function initializeSettings(scrobbler, player, api, ui) {
                             continue;
                         }
                         // Simple two-column format: freq gain (whitespace/tab/comma separated)
-                        const simpleMatch = line.trim().match(/^([\d.]+[kK]?)\s*(?:Hz|kHz)?\s*[,\s\t]+([+-]?[\d.]+)/);
+                        const simpleMatch = line.trim().match(/^([\d.]+)\s*([kK])?(?:Hz)?\s*[,\s\t]+([+-]?[\d.]+)/);
                         if (simpleMatch) {
                             importedPoints.push({
-                                freq: parseGeqLabelFrequency(simpleMatch[1]),
+                                freq: parseGeqLabelFrequency(`${simpleMatch[1]}${simpleMatch[2] || ''}`),
-                                gain: parseFloat(simpleMatch[2]),
+                                gain: parseFloat(simpleMatch[3]),
                             });
                         }
                     }