Function testExpanderBelowThreshold

tests/client_gate_test.cpp:149–177

Signal below threshold, soft expander (ratio 2:1, floor -15 dB): expected reduction = min(floor, (T - env) * (ratio - 1)) with env = -50 dBFS, T = -40 dB, r = 2 → shortfall 10, slope 1 → -10 dB

// expected reduction = min(floor, (T - env) * (ratio - 1))
// with env = -50 dBFS, T = -40 dB, r = 2 → shortfall 10, slope 1 → -10 dB
void testExpanderBelowThreshold()
{
    ClientGate gate;
    gate.prepare(kSampleRate);
    gate.setEnabled(true);
    gate.setThresholdDb(-40.0f);
    gate.setRatio(2.0f);
    gate.setAttackMs(0.5f);
    gate.setReleaseMs(10.0f);       // fast release so envelope settles quickly
    gate.setHoldMs(0.0f);
    gate.setFloorDb(-40.0f);        // deep enough not to clamp the -10 dB expected

    const float ampIn = dbToLin(-50.0f);
    // Long burst for envelope + gain to settle.
    auto prime = makeTone(1000.0, 24000, ampIn);  // 1 s
    processBlocks(gate, prime.data(), 24000);

    const int tailFrames = 512;
    auto tail = makeTone(1000.0, tailFrames, ampIn);
    processBlocks(gate, tail.data(), tailFrames);

    const float outPeak = peakAbsStereo(tail.data(), tailFrames);
    const float grDb = linToDb(outPeak / ampIn);

    // Expected ≈ -10 dB; allow ±1.5 dB for envelope ripple at low frequency.
    report("expander: -50 dBFS → ~-10 dB reduction (2:1)",
           std::fabs(grDb - (-10.0f)) < 1.5f,
           "GR=" + std::to_string(grDb) + " dB (expected ~-10)");
}

// Hard gate (ratio 10:1): signal far below threshold gets clamped to `floor`.
void testGateClampsToRange()