Add selectable RTA filter characteristics

src/state.rs

@@ -321,6 +321,10 @@ fn normalize_rta_config(mut config: PhoenixRtaConfig) -> PhoenixRtaConfig {
         "fft" => "fft".to_string(),
         _ => "iir".to_string(),
     };
+    config.filterbank = match config.filterbank.trim().to_ascii_lowercase().as_str() {
+        "butterworth" | "butter" => "butterworth".to_string(),
+        _ => "legacy".to_string(),
+    };
     config.fft_size = match config.fft_size {
         2048 | 4096 | 8192 | 16384 => config.fft_size,
         n if n < 3072 => 2048,
@@ -721,6 +725,7 @@ mod tests {
             ..PhoenixRtaConfig::default()
         });
         assert_eq!(config.engine, "iir");
+        assert_eq!(config.filterbank, "legacy");
         assert_eq!(config.bpo, "1_12");
         assert_eq!(config.order, 6);
         assert_eq!(config.freq_range, "norm");
@@ -730,6 +735,7 @@ mod tests {
     fn phoenix_profile_retains_explicit_extensions() {
         let config = normalize_rta_config(PhoenixRtaConfig {
             engine: "fft".to_string(),
+            filterbank: "butterworth".to_string(),
             bpo: "1_12".to_string(),
             order: 8,
             freq_range: "lf".to_string(),
@@ -738,6 +744,7 @@ mod tests {
             ..PhoenixRtaConfig::default()
         });
         assert_eq!(config.engine, "fft");
+        assert_eq!(config.filterbank, "butterworth");
         assert_eq!(config.bpo, "1_12");
         assert_eq!(config.order, 8);
         assert_eq!(config.freq_range, "lf");