fm-rds-tx/internal/stereo/delay_test.go

package stereo

import (
	"math"
	"testing"

	"github.com/jan/fm-rds-tx/internal/audio"
)

func TestSSBAndVSBDelayMonoToMatchDiffPath(t *testing.T) {
	const sampleRate = 228000
	const wantDelay = (ssbHilbertTaps - 1) / 2

	for _, mode := range []Mode{ModeSSB, ModeVSB} {
		enc := NewStereoEncoder(sampleRate)
		enc.SetMode(mode, sampleRate)

		for i := 0; i < wantDelay; i++ {
			c := enc.Encode(audio.NewFrame(1, 1))
			if math.Abs(c.Mono) > 1e-12 {
				t.Fatalf("mode %s: mono leaked before delay filled at sample %d: got %.9f want 0", mode, i, c.Mono)
			}
		}

		c := enc.Encode(audio.NewFrame(1, 1))
		if math.Abs(c.Mono-1) > 1e-12 {
			t.Fatalf("mode %s: mono did not emerge after expected delay: got %.9f want 1", mode, c.Mono)
		}
	}
}

func TestDSBMonoRemainsUndelayed(t *testing.T) {
	enc := NewStereoEncoder(228000)
	enc.SetMode(ModeDSB, 228000)
	c := enc.Encode(audio.NewFrame(1, 1))
	if math.Abs(c.Mono-1) > 1e-12 {
		t.Fatalf("DSB mono should be immediate: got %.9f want 1", c.Mono)
	}
}

func TestResetClearsMonoDelayState(t *testing.T) {
	const sampleRate = 228000
	const wantDelay = (ssbHilbertTaps - 1) / 2

	enc := NewStereoEncoder(sampleRate)
	enc.SetMode(ModeSSB, sampleRate)

	for i := 0; i < wantDelay+4; i++ {
		_ = enc.Encode(audio.NewFrame(1, 1))
	}

	enc.Reset()

	for i := 0; i < wantDelay; i++ {
		c := enc.Encode(audio.NewFrame(1, 1))
		if math.Abs(c.Mono) > 1e-12 {
			t.Fatalf("reset did not clear mono delay at sample %d: got %.9f want 0", i, c.Mono)
		}
	}
}