[fix](trx-backend-soapysdr,trx-frontend-http): make wfm mono mode real

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

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

@@ -1252,6 +1252,13 @@ function render(update) {
     if (wfmDeemphasisEl && typeof update.filter.wfm_deemphasis_us === "number") {
       wfmDeemphasisEl.value = String(update.filter.wfm_deemphasis_us);
     }
+    if (wfmAudioModeEl && typeof update.filter.wfm_stereo === "boolean") {
+      const nextMode = update.filter.wfm_stereo ? "stereo" : "mono";
+      if (wfmAudioModeEl.value !== nextMode) {
+        wfmAudioModeEl.value = nextMode;
+        saveSetting("wfmAudioMode", nextMode);
+      }
+    }
     if (wfmDenoiseBtn && typeof update.filter.wfm_denoise === "boolean") {
       const on = update.filter.wfm_denoise;
       wfmDenoiseBtn.textContent = on ? "On" : "Off";
@@ -2587,6 +2594,8 @@ if (wfmAudioModeEl) {
   wfmAudioModeEl.value = loadSetting("wfmAudioMode", "stereo");
   wfmAudioModeEl.addEventListener("change", () => {
     saveSetting("wfmAudioMode", wfmAudioModeEl.value);
+    const enabled = wfmAudioModeEl.value !== "mono";
+    postPath(`/set_wfm_stereo?enabled=${enabled ? "true" : "false"}`).catch(() => {});
   });
 }
 if (wfmDeemphasisEl) {

src/trx-client/trx-frontend/trx-frontend-http/src/api.rs

@@ -486,6 +486,19 @@ pub async fn set_wfm_deemphasis(
     send_command(&rig_tx, RigCommand::SetWfmDeemphasis(query.us)).await
 }
 
+#[derive(serde::Deserialize)]
+pub struct WfmStereoQuery {
+    pub enabled: bool,
+}
+
+#[post("/set_wfm_stereo")]
+pub async fn set_wfm_stereo(
+    query: web::Query<WfmStereoQuery>,
+    rig_tx: web::Data<mpsc::Sender<RigRequest>>,
+) -> Result<HttpResponse, Error> {
+    send_command(&rig_tx, RigCommand::SetWfmStereo(query.enabled)).await
+}
+
 #[post("/toggle_wfm_denoise")]
 pub async fn toggle_wfm_denoise(
     state: web::Data<watch::Receiver<RigState>>,
@@ -713,6 +726,7 @@ pub fn configure(cfg: &mut web::ServiceConfig) {
         .service(set_bandwidth)
         .service(set_fir_taps)
         .service(set_wfm_deemphasis)
+        .service(set_wfm_stereo)
         .service(toggle_wfm_denoise)
         .service(toggle_aprs_decode)
         .service(toggle_cw_decode)

src/trx-core/src/rig/command.rs

@@ -34,6 +34,7 @@ pub enum RigCommand {
     SetBandwidth(u32),
     SetFirTaps(u32),
     SetWfmDeemphasis(u32),
+    SetWfmStereo(bool),
     SetWfmDenoise(bool),
     GetSpectrum,
 }

src/trx-core/src/rig/controller/handlers.rs

@@ -517,6 +517,7 @@ pub fn command_from_rig_command(cmd: RigCommand) -> Box<dyn RigCommandHandler> {
         | RigCommand::SetBandwidth(_)
         | RigCommand::SetFirTaps(_)
         | RigCommand::SetWfmDeemphasis(_)
+        | RigCommand::SetWfmStereo(_)
         | RigCommand::SetWfmDenoise(_)
         | RigCommand::GetSpectrum => Box::new(GetSnapshotCommand),
     }

src/trx-core/src/rig/mod.rs

@@ -175,6 +175,16 @@ pub trait RigCat: Rig + Send {
         )))
     }
 
+    fn set_wfm_stereo<'a>(
+        &'a mut self,
+        _enabled: bool,
+    ) -> Pin<Box<dyn Future<Output = DynResult<()>> + Send + 'a>> {
+        Box::pin(std::future::ready(Err(
+            Box::new(response::RigError::not_supported("set_wfm_stereo"))
+                as Box<dyn std::error::Error + Send + Sync>,
+        )))
+    }
+
     /// Return the current filter state if this backend supports filter controls.
     fn filter_state(&self) -> Option<state::RigFilterState> {
         None

src/trx-core/src/rig/state.rs

@@ -271,6 +271,8 @@ pub struct RigFilterState {
     pub cw_center_hz: u32,
     #[serde(default = "default_wfm_deemphasis_us")]
     pub wfm_deemphasis_us: u32,
+    #[serde(default = "default_wfm_stereo")]
+    pub wfm_stereo: bool,
     #[serde(default = "default_wfm_denoise")]
     pub wfm_denoise: bool,
 }
@@ -283,6 +285,10 @@ fn default_wfm_denoise() -> bool {
     true
 }
 
+fn default_wfm_stereo() -> bool {
+    true
+}
+
 /// Spectrum data from SDR backends (FFT magnitude over the full capture bandwidth).
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct SpectrumData {

src/trx-protocol/src/codec.rs

@@ -298,6 +298,7 @@ mod tests {
                 fir_taps: 64,
                 cw_center_hz: 700,
                 wfm_deemphasis_us: 75,
+                wfm_stereo: true,
                 wfm_denoise: true,
             }),
             ..minimal_snapshot()
@@ -335,6 +336,7 @@ mod tests {
                 fir_taps: 128,
                 cw_center_hz: 700,
                 wfm_deemphasis_us: 50,
+                wfm_stereo: true,
                 wfm_denoise: true,
             }),
             ..minimal_snapshot()

src/trx-protocol/src/mapping.rs

@@ -51,6 +51,7 @@ pub fn client_command_to_rig(cmd: ClientCommand) -> RigCommand {
         ClientCommand::SetWfmDeemphasis { deemphasis_us } => {
             RigCommand::SetWfmDeemphasis(deemphasis_us)
         }
+        ClientCommand::SetWfmStereo { enabled } => RigCommand::SetWfmStereo(enabled),
         ClientCommand::SetWfmDenoise { enabled } => RigCommand::SetWfmDenoise(enabled),
         ClientCommand::GetSpectrum => RigCommand::GetSpectrum,
     }
@@ -96,6 +97,7 @@ pub fn rig_command_to_client(cmd: RigCommand) -> ClientCommand {
         RigCommand::SetWfmDeemphasis(deemphasis_us) => {
             ClientCommand::SetWfmDeemphasis { deemphasis_us }
         }
+        RigCommand::SetWfmStereo(enabled) => ClientCommand::SetWfmStereo { enabled },
         RigCommand::SetWfmDenoise(enabled) => ClientCommand::SetWfmDenoise { enabled },
         RigCommand::GetSpectrum => ClientCommand::GetSpectrum,
     }

src/trx-protocol/src/types.rs

@@ -39,6 +39,7 @@ pub enum ClientCommand {
     SetBandwidth { bandwidth_hz: u32 },
     SetFirTaps { taps: u32 },
     SetWfmDeemphasis { deemphasis_us: u32 },
+    SetWfmStereo { enabled: bool },
     SetWfmDenoise { enabled: bool },
     GetSpectrum,
 }

src/trx-server/src/rig_task.rs

@@ -462,6 +462,16 @@ async fn process_command(
             let _ = ctx.state_tx.send(ctx.state.clone());
             return snapshot_from(ctx.state);
         }
+        RigCommand::SetWfmStereo(enabled) => {
+            if let Err(e) = ctx.rig.set_wfm_stereo(enabled).await {
+                return Err(RigError::communication(format!("set_wfm_stereo: {e}")));
+            }
+            if let Some(f) = ctx.state.filter.as_mut() {
+                f.wfm_stereo = enabled;
+            }
+            let _ = ctx.state_tx.send(ctx.state.clone());
+            return snapshot_from(ctx.state);
+        }
         RigCommand::SetWfmDenoise(enabled) => {
             if let Err(e) = ctx.rig.set_wfm_denoise(enabled).await {
                 return Err(RigError::communication(format!("set_wfm_denoise: {e}")));

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

@@ -345,6 +345,7 @@ impl Deemphasis {
 #[derive(Debug, Clone)]
 pub struct WfmStereoDecoder {
     output_channels: usize,
+    stereo_enabled: bool,
     rds_decoder: RdsDecoder,
     rds_bpf: BiquadBandPass,
     rds_dc: DcBlocker,
@@ -393,6 +394,7 @@ impl WfmStereoDecoder {
         composite_rate: u32,
         audio_rate: u32,
         output_channels: usize,
+        stereo_enabled: bool,
         deemphasis_us: u32,
         denoise_enabled: bool,
     ) -> Self {
@@ -401,6 +403,7 @@ impl WfmStereoDecoder {
         let deemphasis_us = deemphasis_us as f32;
         Self {
             output_channels: output_channels.max(1),
+            stereo_enabled,
             rds_decoder: RdsDecoder::new(composite_rate),
             rds_bpf: BiquadBandPass::new(composite_rate_f, RDS_SUBCARRIER_HZ, RDS_BPF_Q),
             rds_dc: DcBlocker::new(0.995),
@@ -499,7 +502,7 @@ impl WfmStereoDecoder {
             let blend_i = prev_blend + frac * (stereo_blend - prev_blend);
 
             // --- Deemphasis + DC block + output ---
-            if self.output_channels >= 2 {
+            if self.output_channels >= 2 && self.stereo_enabled {
                 // Apply multiband or single-band stereo blend at audio rate.
                 let diff_denoised = if self.denoise_enabled {
                     // Multiband: attenuates high-frequency diff more aggressively
@@ -521,11 +524,14 @@ impl WfmStereoDecoder {
                 // Mono path: apply the pilot notch here so the 19 kHz pilot tone
                 // does not leak into mono audio.  Phase matching with diff is not
                 // a concern for mono, so the notch can sit anywhere in the chain.
-                output.push(
-                    self.dc_m
-                        .process(self.deemph_m.process(self.sum_notch.process(sum_i)))
-                        .clamp(-1.0, 1.0),
-                );
+                let mono = self
+                    .dc_m
+                    .process(self.deemph_m.process(self.sum_notch.process(sum_i)))
+                    .clamp(-1.0, 1.0);
+                output.push(mono);
+                if self.output_channels >= 2 {
+                    output.push(mono);
+                }
             }
         }
 
@@ -536,6 +542,10 @@ impl WfmStereoDecoder {
         self.denoise_enabled = enabled;
     }
 
+    pub fn set_stereo_enabled(&mut self, enabled: bool) {
+        self.stereo_enabled = enabled;
+    }
+
     pub fn rds_data(&self) -> Option<RdsData> {
         self.rds_decoder.snapshot()
     }

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

@@ -309,6 +309,8 @@ pub struct ChannelDsp {
     fir_taps: usize,
     /// WFM deemphasis time constant in microseconds.
     wfm_deemphasis_us: u32,
+    /// Whether WFM stereo decoding is enabled.
+    wfm_stereo: bool,
     /// Whether multiband stereo denoising is enabled for WFM.
     wfm_denoise: bool,
     /// Decimation factor: `sdr_sample_rate / audio_sample_rate`.
@@ -410,6 +412,7 @@ impl ChannelDsp {
                     channel_sample_rate,
                     self.audio_sample_rate,
                     self.output_channels,
+                    self.wfm_stereo,
                     self.wfm_deemphasis_us,
                     self.wfm_denoise,
                 ));
@@ -432,6 +435,7 @@ impl ChannelDsp {
         frame_duration_ms: u16,
         audio_bandwidth_hz: u32,
         wfm_deemphasis_us: u32,
+        wfm_stereo: bool,
         wfm_denoise: bool,
         fir_taps: usize,
         pcm_tx: broadcast::Sender<Vec<f32>>,
@@ -477,6 +481,7 @@ impl ChannelDsp {
             audio_bandwidth_hz,
             fir_taps: taps,
             wfm_deemphasis_us,
+            wfm_stereo,
             wfm_denoise,
             decim_factor,
             output_channels,
@@ -497,6 +502,7 @@ impl ChannelDsp {
                     channel_sample_rate,
                     audio_sample_rate,
                     output_channels,
+                    wfm_stereo,
                     wfm_deemphasis_us,
                     wfm_denoise,
                 ))
@@ -544,6 +550,13 @@ impl ChannelDsp {
         self.rebuild_filters(true);
     }
 
+    pub fn set_wfm_stereo(&mut self, enabled: bool) {
+        self.wfm_stereo = enabled;
+        if let Some(decoder) = &mut self.wfm_decoder {
+            decoder.set_stereo_enabled(enabled);
+        }
+    }
+
     pub fn set_wfm_denoise(&mut self, enabled: bool) {
         self.wfm_denoise = enabled;
         if let Some(decoder) = &mut self.wfm_decoder {
@@ -689,6 +702,7 @@ impl SdrPipeline {
         output_channels: usize,
         frame_duration_ms: u16,
         wfm_deemphasis_us: u32,
+        wfm_stereo: bool,
         wfm_denoise: bool,
         channels: &[(f64, RigMode, u32, usize)],
     ) -> Self {
@@ -711,6 +725,7 @@ impl SdrPipeline {
                 frame_duration_ms,
                 audio_bandwidth_hz,
                 wfm_deemphasis_us,
+                wfm_stereo,
                 wfm_denoise,
                 fir_taps,
                 pcm_tx.clone(),

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

@@ -39,6 +39,8 @@ pub struct SoapySdrRig {
     retune_cmd: Arc<std::sync::Mutex<Option<f64>>>,
     /// Current WFM deemphasis setting in microseconds.
     wfm_deemphasis_us: u32,
+    /// Whether WFM stereo decode is enabled.
+    wfm_stereo: bool,
     /// Whether multiband WFM stereo denoising is enabled.
     wfm_denoise: bool,
 }
@@ -117,6 +119,7 @@ impl SoapySdrRig {
             audio_channels,
             frame_duration_ms,
             wfm_deemphasis_us,
+            true, // wfm_stereo: enabled by default
             true, // wfm_denoise: enabled by default
             channels,
         );
@@ -185,6 +188,7 @@ impl SoapySdrRig {
             center_hz: hardware_center_hz,
             retune_cmd,
             wfm_deemphasis_us,
+            wfm_stereo: true,
             wfm_denoise: true,
         })
     }
@@ -464,6 +468,19 @@ impl RigCat for SoapySdrRig {
         })
     }
 
+    fn set_wfm_stereo<'a>(
+        &'a mut self,
+        enabled: bool,
+    ) -> Pin<Box<dyn std::future::Future<Output = DynResult<()>> + Send + 'a>> {
+        Box::pin(async move {
+            self.wfm_stereo = enabled;
+            if let Some(dsp_arc) = self.pipeline.channel_dsps.get(self.primary_channel_idx) {
+                dsp_arc.lock().unwrap().set_wfm_stereo(enabled);
+            }
+            Ok(())
+        })
+    }
+
     fn set_wfm_denoise<'a>(
         &'a mut self,
         enabled: bool,
@@ -483,6 +500,7 @@ impl RigCat for SoapySdrRig {
             fir_taps: self.fir_taps,
             cw_center_hz: 700,
             wfm_deemphasis_us: self.wfm_deemphasis_us,
+            wfm_stereo: self.wfm_stereo,
             wfm_denoise: self.wfm_denoise,
         })
     }