Add EMA smoothing and hysteresis to detector

cmd/sdrd/main.go

@@ -314,7 +314,9 @@ func main() {
 
 	det := detector.New(cfg.Detector.ThresholdDb, cfg.SampleRate, cfg.FFTSize,
 		time.Duration(cfg.Detector.MinDurationMs)*time.Millisecond,
-		time.Duration(cfg.Detector.HoldMs)*time.Millisecond)
+		time.Duration(cfg.Detector.HoldMs)*time.Millisecond,
+		cfg.Detector.EmaAlpha,
+		cfg.Detector.HysteresisDb)
 
 	window := fftutil.Hann(cfg.FFTSize)
 	h := newHub()
@@ -435,7 +437,9 @@ func main() {
 			if detChanged {
 				newDet = detector.New(next.Detector.ThresholdDb, next.SampleRate, next.FFTSize,
 					time.Duration(next.Detector.MinDurationMs)*time.Millisecond,
-					time.Duration(next.Detector.HoldMs)*time.Millisecond)
+					time.Duration(next.Detector.HoldMs)*time.Millisecond,
+					next.Detector.EmaAlpha,
+					next.Detector.HysteresisDb)
 			}
 			if windowChanged {
 				newWindow = fftutil.Hann(next.FFTSize)

config.yaml

@@ -15,6 +15,8 @@ detector:
   threshold_db: -20
   min_duration_ms: 250
   hold_ms: 500
+  ema_alpha: 0.2
+  hysteresis_db: 3
 recorder:
   enabled: true
   min_snr_db: 10

internal/config/config.go

@@ -17,6 +17,8 @@ type DetectorConfig struct {
 	ThresholdDb   float64 `yaml:"threshold_db" json:"threshold_db"`
 	MinDurationMs int     `yaml:"min_duration_ms" json:"min_duration_ms"`
 	HoldMs        int     `yaml:"hold_ms" json:"hold_ms"`
+	EmaAlpha      float64 `yaml:"ema_alpha" json:"ema_alpha"`
+	HysteresisDb  float64 `yaml:"hysteresis_db" json:"hysteresis_db"`
 }
 
 type RecorderConfig struct {
@@ -79,7 +81,7 @@ func Default() Config {
 		AGC:        false,
 		DCBlock:    false,
 		IQBalance:  false,
-		Detector:   DetectorConfig{ThresholdDb: -20, MinDurationMs: 250, HoldMs: 500},
+		Detector:   DetectorConfig{ThresholdDb: -20, MinDurationMs: 250, HoldMs: 500, EmaAlpha: 0.2, HysteresisDb: 3},
 		Recorder: RecorderConfig{
 			Enabled:     false,
 			MinSNRDb:    10,

internal/detector/detector.go

@@ -22,14 +22,17 @@ type Event struct {
 }
 
 type Detector struct {
-	ThresholdDb float64
-	MinDuration time.Duration
-	Hold        time.Duration
+	ThresholdDb  float64
+	MinDuration  time.Duration
+	Hold         time.Duration
+	EmaAlpha     float64
+	HysteresisDb float64
 
 	binWidth   float64
 	nbins      int
 	sampleRate int
 
+	ema    []float64
 	active map[int64]*activeEvent
 	nextID int64
 }
@@ -57,22 +60,31 @@ type Signal struct {
 	Class    *classifier.Classification `json:"class,omitempty"`
 }
 
-func New(thresholdDb float64, sampleRate int, fftSize int, minDur, hold time.Duration) *Detector {
+func New(thresholdDb float64, sampleRate int, fftSize int, minDur, hold time.Duration, emaAlpha, hysteresis float64) *Detector {
 	if minDur <= 0 {
 		minDur = 250 * time.Millisecond
 	}
 	if hold <= 0 {
 		hold = 500 * time.Millisecond
 	}
+	if emaAlpha <= 0 || emaAlpha > 1 {
+		emaAlpha = 0.2
+	}
+	if hysteresis <= 0 {
+		hysteresis = 3
+	}
 	return &Detector{
-		ThresholdDb: thresholdDb,
-		MinDuration: minDur,
-		Hold:        hold,
-		binWidth:    float64(sampleRate) / float64(fftSize),
-		nbins:       fftSize,
-		sampleRate:  sampleRate,
-		active:      map[int64]*activeEvent{},
-		nextID:      1,
+		ThresholdDb:  thresholdDb,
+		MinDuration:  minDur,
+		Hold:         hold,
+		EmaAlpha:     emaAlpha,
+		HysteresisDb: hysteresis,
+		binWidth:     float64(sampleRate) / float64(fftSize),
+		nbins:        fftSize,
+		sampleRate:   sampleRate,
+		ema:          make([]float64, fftSize),
+		active:       map[int64]*activeEvent{},
+		nextID:       1,
 	}
 }
 
@@ -102,16 +114,18 @@ func (d *Detector) detectSignals(spectrum []float64, centerHz float64) []Signal
 	if n == 0 {
 		return nil
 	}
-	threshold := d.ThresholdDb
-	noise := median(spectrum)
+	smooth := d.smoothSpectrum(spectrum)
+	thresholdOn := d.ThresholdDb
+	thresholdOff := d.ThresholdDb - d.HysteresisDb
+	noise := median(smooth)
 	var signals []Signal
 	in := false
 	start := 0
 	peak := -1e9
 	peakBin := 0
 	for i := 0; i < n; i++ {
-		v := spectrum[i]
-		if v >= threshold {
+		v := smooth[i]
+		if v >= thresholdOn {
 			if !in {
 				in = true
 				start = i
@@ -121,13 +135,13 @@ func (d *Detector) detectSignals(spectrum []float64, centerHz float64) []Signal
 				peak = v
 				peakBin = i
 			}
-		} else if in {
-			signals = append(signals, d.makeSignal(start, i-1, peak, peakBin, noise, centerHz, spectrum))
+		} else if in && v < thresholdOff {
+			signals = append(signals, d.makeSignal(start, i-1, peak, peakBin, noise, centerHz, smooth))
 			in = false
 		}
 	}
 	if in {
-		signals = append(signals, d.makeSignal(start, n-1, peak, peakBin, noise, centerHz, spectrum))
+		signals = append(signals, d.makeSignal(start, n-1, peak, peakBin, noise, centerHz, smooth))
 	}
 	return signals
 }
@@ -147,6 +161,20 @@ func (d *Detector) makeSignal(first, last int, peak float64, peakBin int, noise
 	}
 }
 
+func (d *Detector) smoothSpectrum(spectrum []float64) []float64 {
+	if d.ema == nil || len(d.ema) != len(spectrum) {
+		d.ema = make([]float64, len(spectrum))
+		copy(d.ema, spectrum)
+		return d.ema
+	}
+	alpha := d.EmaAlpha
+	for i := range spectrum {
+		v := spectrum[i]
+		d.ema[i] = alpha*v + (1-alpha)*d.ema[i]
+	}
+	return d.ema
+}
+
 func (d *Detector) matchSignals(now time.Time, signals []Signal) []Event {
 	used := make(map[int64]bool, len(d.active))
 	for _, s := range signals {

internal/detector/detector_test.go

@@ -6,7 +6,7 @@ import (
 )
 
 func TestDetectorCreatesEvent(t *testing.T) {
-	d := New(-10, 1000, 10, 1*time.Millisecond, 10*time.Millisecond)
+	d := New(-10, 1000, 10, 1*time.Millisecond, 10*time.Millisecond, 0.2, 3)
 	center := 0.0
 	spectrum := []float64{-30, -30, -30, -5, -5, -30, -30, -30, -30, -30}
 	now := time.Now()

internal/runtime/runtime.go

@@ -19,9 +19,11 @@ type ConfigUpdate struct {
 }
 
 type DetectorUpdate struct {
-	ThresholdDb *float64 `json:"threshold_db"`
-	MinDuration *int     `json:"min_duration_ms"`
-	HoldMs      *int     `json:"hold_ms"`
+	ThresholdDb  *float64 `json:"threshold_db"`
+	MinDuration  *int     `json:"min_duration_ms"`
+	HoldMs       *int     `json:"hold_ms"`
+	EmaAlpha     *float64 `json:"ema_alpha"`
+	HysteresisDb *float64 `json:"hysteresis_db"`
 }
 
 type SettingsUpdate struct {
@@ -121,6 +123,12 @@ func (m *Manager) ApplyConfig(update ConfigUpdate) (config.Config, error) {
 			}
 			next.Detector.HoldMs = *update.Detector.HoldMs
 		}
+		if update.Detector.EmaAlpha != nil {
+			next.Detector.EmaAlpha = *update.Detector.EmaAlpha
+		}
+		if update.Detector.HysteresisDb != nil {
+			next.Detector.HysteresisDb = *update.Detector.HysteresisDb
+		}
 	}
 	if update.Recorder != nil {
 		if update.Recorder.Enabled != nil {