[fix](trx-backend-soapysdr,trx-frontend-http): reset stereo state and soften wfm top end

Co-authored-by: OpenAI Codex <codex@openai.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/app.js

@@ -964,11 +964,19 @@ function resetRdsDisplay() {
   updateRdsPsOverlay(null);
 }
 
+function resetWfmStereoIndicator() {
+  if (!wfmStFlagEl) return;
+  wfmStFlagEl.textContent = "MO";
+  wfmStFlagEl.classList.remove("wfm-st-flag-stereo");
+  wfmStFlagEl.classList.add("wfm-st-flag-mono");
+}
+
 function applyLocalTunedFrequency(hz, forceDisplay = false) {
   if (!Number.isFinite(hz)) return;
   const freqChanged = lastFreqHz !== hz;
   if (freqChanged) {
     resetRdsDisplay();
+    resetWfmStereoIndicator();
   }
   lastFreqHz = hz;
   updateDocumentTitle(lastSpectrumData?.rds ?? null);

src/trx-server/trx-backend/trx-backend-soapysdr/src/demod.rs

@@ -23,8 +23,6 @@ const BW4_Q1: f32 = 0.5412;
 const BW4_Q2: f32 = 1.3066;
 /// Q for the 19 kHz pilot notch (~3.8 kHz 3 dB bandwidth).
 const PILOT_NOTCH_Q: f32 = 5.0;
-/// Tighter post-matrix stereo notch for suppressing residual pilot leakage.
-const STEREO_PILOT_NOTCH_Q: f32 = 12.0;
 /// Narrow 19 kHz band-pass used to derive zero-crossings for switching stereo demod.
 const PILOT_BPF_Q: f32 = 20.0;
 /// Fixed phase trim on the recovered L-R channel to compensate pilot-path delay.
@@ -362,9 +360,6 @@ pub struct WfmStereoDecoder {
     dc_m: DcBlocker,
     dc_l: DcBlocker,
     dc_r: DcBlocker,
-    /// Post-matrix pilot notches for stereo outputs.
-    pilot_notch_l: BiquadNotch,
-    pilot_notch_r: BiquadNotch,
     deemph_m: Deemphasis,
     deemph_l: Deemphasis,
     deemph_r: Deemphasis,
@@ -431,8 +426,6 @@ impl WfmStereoDecoder {
             dc_m: DcBlocker::new(0.9999),
             dc_l: DcBlocker::new(0.9999),
             dc_r: DcBlocker::new(0.9999),
-            pilot_notch_l: BiquadNotch::new(audio_rate.max(1) as f32, PILOT_HZ, STEREO_PILOT_NOTCH_Q),
-            pilot_notch_r: BiquadNotch::new(audio_rate.max(1) as f32, PILOT_HZ, STEREO_PILOT_NOTCH_Q),
             deemph_m: Deemphasis::new(audio_rate.max(1) as f32, deemphasis_us),
             deemph_l: Deemphasis::new(audio_rate.max(1) as f32, deemphasis_us),
             deemph_r: Deemphasis::new(audio_rate.max(1) as f32, deemphasis_us),
@@ -553,11 +546,11 @@ impl WfmStereoDecoder {
                 let right_corr = (sum_i - diff) * 0.5;
                 let left = self
                     .dc_l
-                    .process(self.pilot_notch_l.process(self.deemph_l.process(left_corr)))
+                    .process(self.deemph_l.process(left_corr))
                     .clamp(-1.0, 1.0);
                 let right = self
                     .dc_r
-                    .process(self.pilot_notch_r.process(self.deemph_r.process(right_corr)))
+                    .process(self.deemph_r.process(right_corr))
                     .clamp(-1.0, 1.0);
                 output.push(left);
                 output.push(right);
@@ -591,6 +584,11 @@ impl WfmStereoDecoder {
         self.rds_decoder.reset();
     }
 
+    pub fn reset_stereo_detect(&mut self) {
+        self.stereo_detect_level = 0.0;
+        self.stereo_detected = false;
+    }
+
     pub fn stereo_detected(&self) -> bool {
         self.stereo_detected
     }

src/trx-server/trx-backend/trx-backend-soapysdr/src/dsp.rs

@@ -568,6 +568,13 @@ impl ChannelDsp {
         }
     }
 
+    pub fn reset_wfm_state(&mut self) {
+        if let Some(decoder) = &mut self.wfm_decoder {
+            decoder.reset_rds();
+            decoder.reset_stereo_detect();
+        }
+    }
+
     /// Process a block of raw IQ samples through the full DSP chain.
     ///
     /// 1. **Batch mixer**: compute the full LO signal for the block at once,
@@ -990,7 +997,7 @@ mod tests {
     fn channel_dsp_processes_silence() {
         let (pcm_tx, _pcm_rx) = broadcast::channel::<Vec<f32>>(8);
         let mut dsp =
-            ChannelDsp::new(0.0, &RigMode::USB, 48_000, 8_000, 1, 20, 3000, 75, true, true, 31, pcm_tx);
+            ChannelDsp::new(0.0, &RigMode::USB, 48_000, 8_000, 1, 20, 3000, 75, true, 31, pcm_tx);
         let block = vec![Complex::new(0.0_f32, 0.0_f32); 4096];
         dsp.process_block(&block);
     }
@@ -999,7 +1006,7 @@ mod tests {
     fn channel_dsp_set_mode() {
         let (pcm_tx, _) = broadcast::channel::<Vec<f32>>(8);
         let mut dsp =
-            ChannelDsp::new(0.0, &RigMode::USB, 48_000, 8_000, 1, 20, 3000, 75, true, true, 31, pcm_tx);
+            ChannelDsp::new(0.0, &RigMode::USB, 48_000, 8_000, 1, 20, 3000, 75, true, 31, pcm_tx);
         assert_eq!(dsp.demodulator, Demodulator::Usb);
         dsp.set_mode(&RigMode::FM);
         assert_eq!(dsp.demodulator, Demodulator::Fm);
@@ -1015,7 +1022,6 @@ mod tests {
             20,
             75,
             true,
-            true,
             &[(200_000.0, RigMode::USB, 3000, 64)],
         );
         assert_eq!(pipeline.pcm_senders.len(), 1);
@@ -1024,7 +1030,7 @@ mod tests {
 
     #[test]
     fn pipeline_empty_channels() {
-        let pipeline = SdrPipeline::start(Box::new(MockIqSource), 1_920_000, 48_000, 1, 20, 75, true, true, &[]);
+        let pipeline = SdrPipeline::start(Box::new(MockIqSource), 1_920_000, 48_000, 1, 20, 75, true, &[]);
         assert_eq!(pipeline.pcm_senders.len(), 0);
         assert_eq!(pipeline.channel_dsps.len(), 0);
     }

src/trx-server/trx-backend/trx-backend-soapysdr/src/lib.rs

@@ -279,7 +279,7 @@ impl RigCat for SoapySdrRig {
                 let mut dsp = dsp_arc.lock().unwrap();
                 dsp.set_channel_if_hz(channel_if_hz);
                 if freq_changed {
-                    dsp.reset_rds();
+                    dsp.reset_wfm_state();
                 }
             }
             Ok(())