Function testFrequencySteering

tests/client_deess_test.cpp:206–246

Moving the frequency knob should steer the sidechain band: a 2 kHz tone that triggered attenuation at freq=2000 should be untouched at freq=10000.

// 2 kHz tone that triggered attenuation at freq=2000 should be
// untouched at freq=10000.
void testFrequencySteering()
{
    ClientDeEss d;
    d.prepare(kSampleRate);
    d.setEnabled(true);
    d.setQ(2.0f);
    d.setThresholdDb(-40.0f);
    d.setAmountDb(-12.0f);
    d.setAttackMs(0.5f);
    d.setReleaseMs(50.0f);

    const float amp = dbToLin(-6.0f);

    // Tuned to 2 kHz — a 2 kHz tone should trigger attenuation.
    d.setFrequencyHz(2000.0f);
    d.reset();
    auto a = makeTone(2000.0, 12000, amp);
    processBlocks(d, a.data(), 12000);
    auto aTail = makeTone(2000.0, 512, amp);
    processBlocks(d, aTail.data(), 512);
    const float grLow = linToDb(peakAbsStereo(aTail.data(), 512) / amp);

    // Move the sidechain up to 10 kHz; same 2 kHz tone should now
    // slip past it.
    d.setFrequencyHz(10000.0f);
    d.reset();
    auto b = makeTone(2000.0, 12000, amp);
    processBlocks(d, b.data(), 12000);
    auto bTail = makeTone(2000.0, 512, amp);
    processBlocks(d, bTail.data(), 512);
    const float grHigh = linToDb(peakAbsStereo(bTail.data(), 512) / amp);

    // With a broad Q=2 bandpass at 10 kHz the 2 kHz tone still leaks
    // some reduction (skirt rolloff, not brick-wall).  The point is
    // that steering produces a significantly different gate response
    // — require at least 5 dB more reduction on the in-tune side.
    report("frequency: steering changes what counts as sibilant",
           grLow < grHigh - 5.0f,
           "grLow=" + std::to_string(grLow)
           + " grHigh=" + std::to_string(grHigh));
}

// Sanity: complex tone with AM modulation produces finite output, no
// NaN/Inf, peak doesn't exceed input.