[fix](trx-rs): sync sdr rds tuning and deemphasis default

Make the primary SoapySDR DSP channel follow the tuned\nfrequency so RDS decoding stays aligned with the active\nfrequency rather than the hardware center.\n\nMove the default WFM deemphasis setting to server SDR\nconfig and default it to 50 us, then pass that value into\nthe SoapySDR backend.\n\nCo-authored-by: Codex <codex@openai.com>

Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-server/src/config.rs

@@ -331,6 +331,8 @@ pub struct SdrConfig {
     pub sample_rate: u32,
     /// Hardware IF filter bandwidth (Hz).
     pub bandwidth: u32,
+    /// WFM deemphasis time constant in microseconds (50 or 75).
+    pub wfm_deemphasis_us: u32,
     /// SDR tunes this many Hz below the dial frequency to keep signal off DC.
     pub center_offset_hz: i64,
     /// Gain configuration.
@@ -344,6 +346,7 @@ impl Default for SdrConfig {
         Self {
             sample_rate: 1_920_000,
             bandwidth: 1_500_000,
+            wfm_deemphasis_us: 50,
             center_offset_hz: 100_000,
             gain: SdrGainConfig::default(),
             channels: Vec::new(),

src/trx-server/src/main.rs

@@ -316,6 +316,7 @@ fn build_sdr_rig_from_instance(
         rig_cfg.audio.sample_rate,
         rig_cfg.audio.channels as usize,
         rig_cfg.audio.frame_duration_ms,
+        rig_cfg.sdr.wfm_deemphasis_us,
         Freq {
             hz: rig_cfg.rig.initial_freq_hz,
         },

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

@@ -296,6 +296,15 @@ pub struct ChannelDsp {
 }
 
 impl ChannelDsp {
+    pub fn set_channel_if_hz(&mut self, channel_if_hz: f64) {
+        self.channel_if_hz = channel_if_hz;
+        self.mixer_phase_inc = if self.sdr_sample_rate == 0 {
+            0.0
+        } else {
+            2.0 * std::f64::consts::PI * channel_if_hz / self.sdr_sample_rate as f64
+        };
+    }
+
     fn pipeline_rates(
         mode: &RigMode,
         sdr_sample_rate: u32,

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

@@ -73,6 +73,7 @@ impl SoapySdrRig {
         audio_sample_rate: u32,
         audio_channels: usize,
         frame_duration_ms: u16,
+        wfm_deemphasis_us: u32,
         initial_freq: Freq,
         initial_mode: RigMode,
         sdr_sample_rate: u32,
@@ -113,7 +114,7 @@ impl SoapySdrRig {
             audio_sample_rate,
             audio_channels,
             frame_duration_ms,
-            75,
+            wfm_deemphasis_us,
             channels,
         );
 
@@ -180,7 +181,7 @@ impl SoapySdrRig {
             center_offset_hz,
             center_hz: hardware_center_hz,
             retune_cmd,
-            wfm_deemphasis_us: 75,
+            wfm_deemphasis_us,
         })
     }
 
@@ -196,6 +197,7 @@ impl SoapySdrRig {
             48_000,
             1,
             20,
+            50,
             Freq { hz: 144_300_000 },
             RigMode::USB,
             1_920_000,
@@ -266,6 +268,11 @@ impl RigCat for SoapySdrRig {
                     *cmd = Some(hardware_hz as f64);
                 }
             }
+
+            if let Some(dsp_arc) = self.pipeline.channel_dsps.get(self.primary_channel_idx) {
+                let channel_if_hz = (self.freq.hz as i64 - self.center_hz) as f64;
+                dsp_arc.lock().unwrap().set_channel_if_hz(channel_if_hz);
+            }
             Ok(())
         })
     }
@@ -280,6 +287,10 @@ impl RigCat for SoapySdrRig {
             if let Ok(mut cmd) = self.retune_cmd.lock() {
                 *cmd = Some(self.center_hz as f64);
             }
+            if let Some(dsp_arc) = self.pipeline.channel_dsps.get(self.primary_channel_idx) {
+                let channel_if_hz = (self.freq.hz as i64 - self.center_hz) as f64;
+                dsp_arc.lock().unwrap().set_channel_if_hz(channel_if_hz);
+            }
             Ok(())
         })
     }