Add selectable RTA filter characteristics

www/core/audio.js

@@ -516,6 +516,7 @@ function buildPhoenixMeterPacket(frame) {
     xyR,
     rta: rta ? {
       engine: String(rta?.engine || 'iir'),
+      filterbank: String(rta?.filterbank || 'legacy'),
       bands_avg: Array.isArray(rta?.bands_avg) ? rta.bands_avg : (Array.isArray(rta?.bands) ? rta.bands : []),
       bands_peak: Array.isArray(rta?.bands_peak) ? rta.bands_peak : [],
       bands: Array.isArray(rta?.bands) ? rta.bands : (Array.isArray(rta?.bands_avg) ? rta.bands_avg : []),
@@ -871,6 +872,7 @@ export function buildRtaRuntimeConfig(CONFIG = {}) {
   const runtimeBpoMode = bpoMode;
   return {
     engine: rtwProfile ? 'iir' : (CONFIG.RTA_ENGINE || 'iir'),
+    filterbank: CONFIG.RTA_IIR_FILTERBANK === 'butterworth' ? 'butterworth' : 'legacy',
     fftSize: CONFIG.FFT_SIZE || 4096,
     monoInput: !!CONFIG.MONO_INPUT,
     lrFractionalDelayEnabled: !!CONFIG.LR_FRACTIONAL_DELAY_ENABLED,

www/core/config.js

@@ -50,6 +50,7 @@ const CONFIG = {
   REALTIME_BAR_HOLD_MS: 800,
   REALTIME_BAR_DECAY_DB_PER_S: 20,
   RTA_ENGINE: 'iir',             // 'fft' | 'iir'
+  RTA_IIR_FILTERBANK: 'legacy',  // 'legacy' | 'butterworth'
   RTA_FREQ_RANGE: 'norm',        // 'norm' | 'lf'
   RTA_BPO_MODE: '1_3',
   RTA_WEIGHTING: 'z',            // 'z' | 'a' | 'c'
@@ -784,6 +785,9 @@ function loadConfig(opts = {}) {
     if (typeof saved.PPM_DIN_DECAY_DB_PER_S === 'number') CONFIG.PPM_DIN_DECAY_DB_PER_S = saved.PPM_DIN_DECAY_DB_PER_S;
     if (typeof saved.PPM_DIN_HOLD_MS === 'number') CONFIG.PPM_DIN_HOLD_MS = saved.PPM_DIN_HOLD_MS;
     if (CONFIG.RTA_BAR_LAYOUT === 'classic') CONFIG.RTA_BAR_LAYOUT = 'rtw';
+    CONFIG.RTA_IIR_FILTERBANK = CONFIG.RTA_IIR_FILTERBANK === 'butterworth'
+      ? 'butterworth'
+      : 'legacy';
     if (CONFIG.RTA_BAR_LAYOUT === 'rtw') {
       CONFIG.RTA_ENGINE = 'iir';
       CONFIG.RTA_IIR_ORDER = 6;