Add WFM de-emphasis and stabilize live audio playback

internal/demod/fm.go

@@ -109,6 +109,20 @@ func RDSBaseband(iq []complex64, sampleRate int) []float32 {
 	return dsp.ApplyFIRReal(out, lp)
 }
 
+func deemphasis(x []float32, sampleRate int, tau float64) []float32 {
+	if len(x) == 0 || sampleRate <= 0 {
+		return x
+	}
+	alpha := math.Exp(-1.0 / (float64(sampleRate) * tau))
+	out := make([]float32, len(x))
+	var y float64
+	for i, v := range x {
+		y = alpha*y + (1-alpha)*float64(v)
+		out[i] = float32(y)
+	}
+	return out
+}
+
 func init() {
 	Register(NFM{})
 	Register(WFM{})

web/app.js

@@ -92,6 +92,7 @@ const liveListenBtn = qs('liveListenBtn');
 
 let latest = null;
 let currentConfig = null;
+let liveAudio = null;
 let stats = { buffer_samples: 0, dropped: 0, resets: 0, last_sample_ago_ms: -1 };
 let gpuInfo = { available: false, active: false, error: '' };
 
@@ -1327,3 +1328,5 @@ setInterval(loadGPU, 1000);
 setInterval(() => fetchEvents(false), 2000);
 setInterval(fetchRecordings, 5000);
 setInterval(loadSignals, 1500);
+ordings, 5000);
+setInterval(loadSignals, 1500);