fix: resolve remaining PR #523 review issues

Guard generateFrequencies against bandCount=1 division by zero, fix
inverted HRTF ITD delays for left-side sources, remove unused variable,
promote _interpolateGains to public API, and add NaN guard to widening.

js/audio-context.js

@@ -12,6 +12,12 @@ function generateFrequencies(bandCount, minFreq = 20, maxFreq = 20000) {
     const safeMin = Math.max(10, minFreq);
     const safeMax = Math.min(96000, maxFreq);
 
+    if (bandCount <= 1) {
+        // Single band: use geometric mean of range
+        frequencies.push(Math.round(Math.sqrt(safeMin * safeMax)));
+        return frequencies;
+    }
+
     for (let i = 0; i < bandCount; i++) {
         // Logarithmic interpolation
         const t = i / (bandCount - 1);
@@ -175,7 +181,7 @@ class AudioContextManager {
         this.frequencies = generateFrequencies(newCount, this.freqRange.min, this.freqRange.max);
 
         // Interpolate current gains to new band count
-        const newGains = equalizerSettings._interpolateGains(this.currentGains, newCount);
+        const newGains = equalizerSettings.interpolateGains(this.currentGains, newCount);
         this.currentGains = newGains;
         equalizerSettings.setGains(newGains);
 
@@ -1079,7 +1085,7 @@ class AudioContextManager {
         // Ensure gains array matches current band count
         let adjustedGains = gains;
         if (gains.length !== this.bandCount) {
-            adjustedGains = equalizerSettings._interpolateGains(gains, this.bandCount);
+            adjustedGains = equalizerSettings.interpolateGains(gains, this.bandCount);
         }
 
         const now = this.audioContext?.currentTime || 0;
@@ -1535,7 +1541,7 @@ class AudioContextManager {
         const oldGains = this.geqGains;
         this.geqBandCount = newCount;
         this.geqFrequencies = generateFrequencies(newCount, this.geqFreqRange.min, this.geqFreqRange.max);
-        this.geqGains = equalizerSettings._interpolateGains(oldGains, newCount);
+        this.geqGains = equalizerSettings.interpolateGains(oldGains, newCount);
 
         equalizerSettings.setGraphicEqBandCount(newCount);
         equalizerSettings.setGraphicEqGains(this.geqGains);

js/equalizer.js

@@ -201,7 +201,7 @@ export class Equalizer {
         this.frequencyLabels = generateFrequencyLabels(this.frequencies);
 
         // Interpolate current gains to new band count
-        const newGains = equalizerSettings._interpolateGains(this.currentGains, newCount);
+        const newGains = equalizerSettings.interpolateGains(this.currentGains, newCount);
         this.currentGains = newGains;
         equalizerSettings.setGains(newGains);
 
@@ -455,7 +455,7 @@ export class Equalizer {
         // Ensure gains array matches current band count
         let adjustedGains = gains;
         if (gains.length !== this.bandCount) {
-            adjustedGains = equalizerSettings._interpolateGains(gains, this.bandCount);
+            adjustedGains = equalizerSettings.interpolateGains(gains, this.bandCount);
         }
 
         const now = this.audioContext?.currentTime || 0;

js/hrtf-generator.js

@@ -65,8 +65,9 @@ export function generateHRTF(audioContext, azimuthDeg, elevationDeg = 0) {
     const contraData = sourceOnRight ? leftData : rightData;
 
     // Generate ipsilateral (near ear) IR — mostly a delayed impulse with slight coloring
-    const ipsiDelay = Math.max(0, sourceOnRight ? 0 : itdSamples);
+    // Ipsilateral ear (near source) receives sound first; contralateral ear is delayed by ITD
-    const contraDelay = Math.max(0, sourceOnRight ? itdSamples : 0);
+    const ipsiDelay = 0;
+    const contraDelay = Math.abs(itdSamples);
 
     // Create frequency-domain representation for head shadow
     const fftSize = IR_LENGTH;

js/settings.js

@@ -1512,7 +1512,7 @@ export async function initializeSettings(scrobbler, player, api, ui) {
             const newCount = Math.max(3, Math.min(32, parseInt(geqBandCountInput.value, 10) || 16));
             geqBandCountInput.value = newCount;
             if (newCount === geqBandCount) return;
-            geqGains = equalizerSettings._interpolateGains(geqGains, newCount);
+            geqGains = equalizerSettings.interpolateGains(geqGains, newCount);
             geqBandCount = newCount;
             equalizerSettings.setGraphicEqGains(geqGains);
             audioContextManager.setGraphicEqBandCount(newCount);
@@ -1778,7 +1778,7 @@ export async function initializeSettings(scrobbler, player, api, ui) {
                     return;
                 }
                 const adjusted =
-                    gains.length !== geqBandCount ? equalizerSettings._interpolateGains(gains, geqBandCount) : gains;
+                    gains.length !== geqBandCount ? equalizerSettings.interpolateGains(gains, geqBandCount) : gains;
                 geqGains = adjusted.map((g) => {
                     const n = Number(g);
                     return Number.isFinite(n)
@@ -2446,7 +2446,6 @@ export async function initializeSettings(scrobbler, player, api, ui) {
             else if (meas) graphShift = 75 - getNormalizationOffset(meas);
         }
 
-        const sampleRate = autoeqSampleRate ? parseInt(autoeqSampleRate.value, 10) : 48000;
         let closest = -1,
             closestDist = Infinity;
         activeBands.forEach((band, i) => {

js/storage.js

@@ -1329,7 +1329,7 @@ export const equalizerSettings = {
                     }
                     // If different band count, try to interpolate or return flat
                     if (gains.length > 0) {
-                        return this._interpolateGains(gains, count);
+                        return this.interpolateGains(gains, count);
                     }
                 }
             }
@@ -1425,7 +1425,7 @@ export const equalizerSettings = {
                 }
                 // Interpolate stored Qs to match requested band count instead of discarding
                 if (Array.isArray(qs) && qs.length >= this.MIN_BANDS) {
-                    return this._interpolateGains(qs, count);
+                    return this.interpolateGains(qs, count);
                 }
             }
         } catch {
@@ -1473,7 +1473,7 @@ export const equalizerSettings = {
     /**
      * Interpolate gains array to match target band count
      */
-    _interpolateGains(sourceGains, targetCount) {
+    interpolateGains(sourceGains, targetCount) {
         if (sourceGains.length === targetCount) {
             return [...sourceGains];
         }
@@ -1808,7 +1808,7 @@ export const equalizerSettings = {
                     return parsed.map((v) => (Number.isFinite(v) ? v : 0));
                 }
                 if (Array.isArray(parsed) && parsed.length > 0) {
-                    return this._interpolateGains(parsed, expectedCount);
+                    return this.interpolateGains(parsed, expectedCount);
                 }
             }
         } catch {
@@ -1944,7 +1944,8 @@ export const binauralDspSettings = {
 
     setWideningAmount(amount) {
         const all = this._getAll();
-        all.wideningAmount = Math.max(0, Math.min(2, amount));
+        const n = Number(amount);
+        all.wideningAmount = Number.isFinite(n) ? Math.max(0, Math.min(2, n)) : 1.0;
         this._setAll(all);
     },