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Add an Oberheim-SEM morph law to the SVF filter: HP->notch->LP alongside HP->BP->LP, selected at prepare() time, free on the per-sample path

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This commit is contained in:
Daniel Harvey
2026-07-30 10:22:49 -04:00
parent f12700c997
commit d2364eb5ac
10 changed files with 971 additions and 483 deletions
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tests/test_filter.cpp
+263 -441
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@@ -1,8 +1,11 @@
// Standalone tests for the per-voice TPT/SVF filter — no VST3, no REAPER, no framework. Same
// fast assert loop as the sibling pure tests. The coefficient pins are literals so a refactor
// that changes the DSP fails loudly; they are cross-checked in-test against a derivation that
// shares no code with the implementation, and the responses against the analog 2-pole prototype
// evaluated at the bilinear-warped frequency.
// Standalone tests for the RUNNING per-voice TPT/SVF filter — no VST3, no REAPER, no framework.
// Same fast assert loop as the sibling pure tests. The coefficient pins are literals so a
// refactor that changes the DSP fails loudly; they are cross-checked in-test against a derivation
// that shares no code with the implementation, and the responses against the analog 2-pole
// prototype evaluated at the bilinear-warped frequency. Sibling targets own the neighbouring
// domains: test_filter_params.cpp the control mappings, test_filter_morph.cpp the pure morph-weight
// algebra, test_filter_state.cpp the numerical/state behaviour. This file owns the analytic
// reference and the steady-state gain measurement, and everything here uses them.
#include "../src/core/instrument/engine/filter/filter_coeffs.h"
#include "../src/core/instrument/engine/filter/filter_morph.h"
@@ -10,11 +13,9 @@
#include "../src/core/instrument/engine/filter/filter_saturate.h"
#include "../src/core/instrument/engine/filter/voice_filter.h"
#include <cfloat>
#include <cmath>
#include <cstdio>
#include <initializer_list>
#include <limits>
using namespace reasampler::instrument::engine::filter;
@@ -28,11 +29,18 @@ static int g_fail = 0;
static constexpr double kPi = 3.14159265358979323846;
// Morph positions of the three pure taps.
// Morph positions. The endpoints are the same pure taps under both laws; only the centre differs
// — a band-pass under HighBandLow, a notch under HighNotchLow.
static constexpr float kHighPass = 0.0f;
static constexpr float kBandPass = 0.5f;
static constexpr float kCentre = 0.5f;
static constexpr float kLowPass = 1.0f;
static const MorphLaw kBothLaws[] = {MorphLaw::HighBandLow, MorphLaw::HighNotchLow};
static const char* lawName(MorphLaw law) {
return law == MorphLaw::HighBandLow ? "HP-BP-LP" : "HP-notch-LP";
}
// The rates the invariance claims are made over.
static const double kRates[] = {44100.0, 48000.0, 88200.0, 96000.0, 192000.0};
static constexpr int kRateCount = 5;
@@ -75,101 +83,9 @@ static double measuredGain(const FilterSettings& fs, double sr, double freq, dou
return std::sqrt(sumSq / measure) / (amp / std::sqrt(2.0));
}
static FilterSettings at(double fcHz, float res, float morph, float drive = 0.0f) {
return {filterNormFromCutoffHz(static_cast<float>(fcHz)), res, morph, drive};
}
// ---------------------------------------------------------------------------
// Control mappings (carried over — the cutoff and Q laws are unchanged)
// ---------------------------------------------------------------------------
static void testCutoffMapsThreeDecadesLogarithmically() {
CHECK_NEAR(filterCutoffHzFromNorm(0.0f), 20.0, 1e-3);
CHECK_NEAR(filterCutoffHzFromNorm(1.0f), 20000.0, 1e-2);
// Exactly three decades, so the decade midpoints land on round numbers.
CHECK_NEAR(filterCutoffHzFromNorm(1.0f / 3.0f), 200.0, 1e-3);
CHECK_NEAR(filterCutoffHzFromNorm(2.0f / 3.0f), 2000.0, 1e-2);
// Half-decade steps confirm the sweep is log, not linear.
CHECK_NEAR(filterCutoffHzFromNorm(1.0f / 6.0f), 20.0 * std::sqrt(10.0), 1e-3);
CHECK_NEAR(filterCutoffHzFromNorm(0.5f), 20.0 * std::sqrt(1000.0), 1e-2);
CHECK_NEAR(filterCutoffHzFromNorm(-1.0f), 20.0, 1e-3);
CHECK_NEAR(filterCutoffHzFromNorm(2.0f), 20000.0, 1e-2);
}
static void testCutoffNormRoundTrips() {
for (int i = 0; i <= 20; ++i) {
const float n = static_cast<float>(i) / 20.0f;
CHECK_NEAR(filterNormFromCutoffHz(filterCutoffHzFromNorm(n)), n, 1e-6);
}
CHECK_NEAR(filterNormFromCutoffHz(200.0f), 1.0 / 3.0, 1e-6);
CHECK(filterNormFromCutoffHz(1.0f) == 0.0f);
CHECK(filterNormFromCutoffHz(48000.0f) == 1.0f);
}
static void testQSpansPointOneToTenWithRootTwoAtCenter() {
CHECK_NEAR(filterQFromNorm(0.0f), 0.1, 1e-6);
CHECK_NEAR(filterQFromNorm(0.5f), std::sqrt(2.0), 1e-5);
CHECK_NEAR(filterQFromNorm(1.0f), 10.0, 1e-4);
CHECK_NEAR(filterQFromNorm(-1.0f), 0.1, 1e-6);
CHECK_NEAR(filterQFromNorm(2.0f), 10.0, 1e-4);
// Pins the single quadratic-in-log-Q curve at two interior points, derived independently by
// solving log Q = a + b*n + c*n^2 through the three anchors above rather than read out of
// the implementation. A two-spliced-log-segments curve (log-linear on each half, the design
// this module doc explicitly rejects for its center-detent slope kink) would give 0.376 and
// 3.761 here instead — both comfortably outside this tolerance.
{
const double lo = std::log(static_cast<double>(kFilterQMin));
const double mid = std::log(static_cast<double>(kFilterQCenter));
const double hi = std::log(static_cast<double>(kFilterQMax));
const double c = 2.0 * lo + 2.0 * hi - 4.0 * mid;
const double b = hi - lo - c;
const double a = lo;
auto qLaw = [&](double n) { return std::exp(a + b * n + c * n * n); };
CHECK_NEAR(filterQFromNorm(0.25f), qLaw(0.25), 1e-5);
CHECK_NEAR(filterQFromNorm(0.75f), qLaw(0.75), 1e-5);
}
// Strictly monotonic across the whole travel — no fold-back from the quadratic term.
float prev = -1.0f;
for (int i = 0; i <= 1000; ++i) {
const float q = filterQFromNorm(static_cast<float>(i) / 1000.0f);
CHECK(q > prev);
prev = q;
}
}
static void testQNormRoundTrips() {
for (int i = 0; i <= 20; ++i) {
const float n = static_cast<float>(i) / 20.0f;
CHECK_NEAR(filterNormFromQ(filterQFromNorm(n)), n, 1e-5);
}
CHECK_NEAR(filterNormFromQ(static_cast<float>(std::sqrt(2.0))), 0.5, 1e-5);
CHECK(filterNormFromQ(0.0f) == 0.0f);
CHECK(filterNormFromQ(1000.0f) == 1.0f);
}
static void testDriveDepthIsZeroAtRestAndRisesMonotonically() {
// Exactly zero, not nearly: the limiter is the identity only at depth 0.
CHECK(filterDriveDepthFromNorm(0.0f) == 0.0f);
CHECK(filterDriveDepthFromNorm(-1.0f) == 0.0f);
CHECK_NEAR(filterDriveDepthFromNorm(1.0f), kFilterDriveDepthMax, 1e-6);
CHECK_NEAR(filterDriveDepthFromNorm(2.0f), kFilterDriveDepthMax, 1e-6);
// Pins the SQUARE law at an interior point, not just the anchors: a linear law would give
// kFilterDriveDepthMax/2 (2.0) here, not kFilterDriveDepthMax/4 (1.0).
CHECK_NEAR(filterDriveDepthFromNorm(0.5f), kFilterDriveDepthMax * 0.25, 1e-6);
float prev = -1.0f;
for (int i = 0; i <= 100; ++i) {
const float d = filterDriveDepthFromNorm(static_cast<float>(i) / 100.0f);
CHECK(d > prev);
prev = d;
}
static FilterSettings at(double fcHz, float res, float morph, float drive = 0.0f,
MorphLaw law = MorphLaw::HighBandLow) {
return {filterNormFromCutoffHz(static_cast<float>(fcHz)), res, morph, drive, law};
}
// ---------------------------------------------------------------------------
@@ -253,88 +169,47 @@ static void testNonPositiveRatePassesSignalThroughAtEveryMorph() {
}
// ---------------------------------------------------------------------------
// Morph
// Morph — measured, under both laws
// ---------------------------------------------------------------------------
// The endpoints are pure taps EXACTLY, not to within a rounding of cos/sin. Asserted on the
// folded mix, where "pure" is an exact statement about three floats.
static void testMorphEndpointMixesAreExactlyPureTaps() {
const float k = 1.0f / filterQFromNorm(0.5f);
const MorphMix hp = morphMix(morphWeights(kHighPass), k);
CHECK(hp.m0 == 1.0f && hp.m1 == -k && hp.m2 == -1.0f); // v0 - k*v1 - v2
const MorphMix bp = morphMix(morphWeights(kBandPass), k);
CHECK(bp.m0 == 0.0f && bp.m1 == 1.0f && bp.m2 == 0.0f); // v1
const MorphMix lp = morphMix(morphWeights(kLowPass), k);
CHECK(lp.m0 == 0.0f && lp.m1 == 0.0f && lp.m2 == 1.0f); // v2
// Out-of-range clamps to the endpoints rather than extrapolating.
CHECK(morphWeights(-1.0f).hp == 1.0f);
CHECK(morphWeights(2.0f).lp == 1.0f);
// NaN clamps to neither endpoint (every comparison against it is false) and lands on pure
// band-pass instead -- no crash, a sane fallback rather than an extrapolation.
const MorphWeights nanW = morphWeights(std::numeric_limits<float>::quiet_NaN());
CHECK(nanW.hp == 0.0f && nanW.bp == 1.0f && nanW.lp == 0.0f);
}
// Pins the cos/sin curve at an interior point, not just the endpoints and the quadrature
// identity (hp^2+bp^2+lp^2=1, which any equal-power reparameterization would also satisfy).
// theta=0.5*pi*t^2 (quadratic in the leg fraction, still equal-power, still exact at both
// ends) would give hp=0.9239/bp=0.3827 here instead of the cos/sin pair's 0.7071/0.7071.
static void testMorphInteriorPointMatchesCosSinNotAnAlternateEqualPowerCurve() {
const MorphWeights w = morphWeights(0.25f); // HP->BP leg, t = 2*0.25 = 0.5
const double theta = 0.5 * kPi * 0.5;
CHECK_NEAR(w.hp, std::cos(theta), 1e-6);
CHECK_NEAR(w.bp, std::sin(theta), 1e-6);
CHECK(w.lp == 0.0f);
}
// HP and LP never carry weight at the same time. That is what keeps the centre a band-pass
// instead of the Oberheim SEM's notch: the two are antiphase at the corner and would cancel.
static void testMorphNeverBlendsHighAgainstLowPass() {
for (int i = 0; i <= 200; ++i) {
const MorphWeights w = morphWeights(static_cast<float>(i) / 200.0f);
CHECK(w.hp == 0.0f || w.lp == 0.0f);
CHECK(w.hp >= 0.0f && w.bp >= 0.0f && w.lp >= 0.0f);
// Equal power: the active pair sums in quadrature to unity.
CHECK_NEAR(w.hp * w.hp + w.bp * w.bp + w.lp * w.lp, 1.0, 1e-6);
}
}
// The endpoints are exact 2-pole HP and LP under BOTH laws; only the centre is law-specific, so
// the centre is asserted here only for the law that has a pure tap there.
static void testMorphEndpointsMatchTheAnalyticTwoPoleTargets() {
const double sr = 48000.0, fc = 1000.0;
for (float res : {0.0f, 0.5f, 1.0f}) {
const double q = filterQFromNorm(res);
for (float morph : {kHighPass, kBandPass, kLowPass}) {
for (double f : {125.0, 500.0, 1000.0, 2000.0, 8000.0}) {
const double got = measuredGain(at(fc, res, morph), sr, f);
const double want = analyticMag(morph, f, fc, q, sr);
if (!(std::fabs(got / want - 1.0) <= kAgreement)) {
std::printf("FAIL line %d: morph %.1f res %.1f at %.0f Hz: %.6f vs analytic "
"%.6f (%.3f%%)\n",
__LINE__, morph, res, f, got, want,
(got / want - 1.0) * 100.0);
++g_fail;
for (MorphLaw law : kBothLaws) {
for (float res : {0.0f, 0.5f, 1.0f}) {
const double q = filterQFromNorm(res);
for (float morph : {kHighPass, kBandPass, kLowPass}) {
if (morph == kBandPass && law != MorphLaw::HighBandLow) continue;
for (double f : {125.0, 500.0, 1000.0, 2000.0, 8000.0}) {
const double got = measuredGain(at(fc, res, morph, 0.0f, law), sr, f);
const double want = analyticMag(morph, f, fc, q, sr);
if (!(std::fabs(got / want - 1.0) <= kAgreement)) {
std::printf("FAIL line %d: %s morph %.1f res %.1f at %.0f Hz: %.6f vs "
"analytic %.6f (%.3f%%)\n",
__LINE__, lawName(law), morph, res, f, got, want,
(got / want - 1.0) * 100.0);
++g_fail;
}
}
}
}
}
}
// The reason the blend is equal-power rather than linear. At the corner the three taps are
// HP = jQ, BP = Q, LP = -jQ — adjacent taps in exact quadrature — so a cos/sin pair holds the
// corner magnitude at exactly Q the whole way across. A linear crossfade would sag to Q/sqrt(2)
// mid-leg, a 3 dB hole that would read as a defect rather than as character.
static void testCornerMagnitudeIsFlatAcrossTheWholeMorphSweep() {
// LAW-SPECIFIC, and deliberately not generalized: this guarantee belongs to HighBandLow alone.
// At the corner the three taps are HP = jQ, BP = Q, LP = -jQ — ADJACENT taps in exact quadrature
// — so a cos/sin pair holds the corner magnitude at exactly Q the whole way across. A linear
// crossfade would sag to Q/sqrt(2) mid-leg, a 3 dB hole that would read as a defect rather than
// as character. HighNotchLow deliberately violates this (its corner magnitude goes to zero at the
// centre); weakening this assertion to accommodate that law would throw the guarantee away.
static void testCornerMagnitudeIsFlatAtQAcrossTheHighBandLowSweep() {
const double sr = 48000.0, fc = 1000.0;
for (float res : {0.0f, 0.5f, 1.0f}) {
const double q = filterQFromNorm(res);
for (int i = 0; i <= 16; ++i) {
const float m = static_cast<float>(i) / 16.0f;
const double got = measuredGain(at(fc, res, m), sr, fc);
const double got = measuredGain(at(fc, res, m, 0.0f, MorphLaw::HighBandLow), sr, fc);
if (!(std::fabs(got / q - 1.0) <= kAgreement)) {
std::printf("FAIL line %d: morph %.4f res %.1f corner gain %.6f, expected Q "
"%.6f (%.3f%%)\n",
@@ -345,38 +220,163 @@ static void testCornerMagnitudeIsFlatAcrossTheWholeMorphSweep() {
}
}
// Continuity as a control, not just at the corner: no step between adjacent morph positions at
// any fixed frequency. A coefficient switch at the centre — the thing an enum would have forced —
// shows up here as a jump.
static void testMorphSweepHasNoDiscontinuity() {
const double sr = 48000.0, fc = 1000.0;
constexpr int kSteps = 40;
for (float res : {0.0f, 0.5f, 1.0f}) {
for (double f : {250.0, 1000.0, 4000.0}) {
double prev = -1.0;
for (int i = 0; i <= kSteps; ++i) {
const float m = static_cast<float>(i) / kSteps;
const double got = measuredGain(at(fc, res, m), sr, f);
if (prev >= 0.0) {
// Scaled by the response's own magnitude at this setting — the passband is
// unity and the corner is Q, so below Q=1 the passband is what a step has to
// be small against, not Q.
const double scale = std::fmax(1.0, filterQFromNorm(res));
// One step is 1/40 of the travel; the steepest leg moves well under a tenth
// of that scale over one step (measured worst case is 0.03).
const double jump = std::fabs(got - prev) / scale;
if (!(jump < 0.1)) {
std::printf("FAIL line %d: morph %.4f res %.1f at %.0f Hz jumps %.4f\n",
__LINE__, m, res, f, jump);
++g_fail;
}
// The SEM's centre is a genuine null, not merely a dip: the corner magnitude falls to the float
// noise floor because HP and LP sit at exactly +90 and -90 degrees there, so equal weights cancel
// by construction. Measured worst case across this whole grid is 3.8e-05 (-88 dB); the typical
// figure is -110 to -145 dB. The settle window has to clear the resonator's ring-down before the
// residual means anything — at 0.15 s and Q=10 the leftover transient alone reads as -52 dB and
// would be mistaken for the floor.
static void testHighNotchLowCentreIsATrueNullAtTheCorner() {
for (int r = 0; r < kRateCount; ++r) {
for (double fc : {250.0, 1000.0, 4000.0}) {
for (float res : {0.0f, 0.5f, 1.0f}) {
const double got = measuredGain(at(fc, res, kCentre, 0.0f, MorphLaw::HighNotchLow),
kRates[r], fc, 0.25, 2.0, 0.5);
if (!(got < 2e-4)) {
std::printf("FAIL line %d: SEM notch at sr %.0f fc %.0f res %.1f is %.3e "
"(%.1f dB) — not a null\n",
__LINE__, kRates[r], fc, res, got,
20.0 * std::log10(got + 1e-300));
++g_fail;
}
prev = got;
}
}
}
}
// The null sits AT the cutoff, not merely somewhere nearby: the response falls monotonically into
// fc from both sides and is orders of magnitude below its own immediate neighbours. At fc=1 kHz,
// +/-5% off the notch already reads -20 dB while the notch itself reads -127 dB.
static void testHighNotchLowNullIsLocatedAtTheCutoff() {
const double sr = 48000.0, fc = 1000.0;
for (float res : {0.0f, 0.5f, 1.0f}) {
const FilterSettings fs = at(fc, res, kCentre, 0.0f, MorphLaw::HighNotchLow);
const double below[] = {0.5, 0.8, 0.95};
double prev = 1e30;
for (double ratio : below) {
const double got = measuredGain(fs, sr, fc * ratio);
CHECK(got < prev);
prev = got;
}
const double atCorner = measuredGain(fs, sr, fc, 0.25, 2.0, 0.5);
CHECK(atCorner < prev);
prev = atCorner;
for (double ratio : {1.05, 1.25, 2.0}) {
const double got = measuredGain(fs, sr, fc * ratio);
CHECK(got > prev);
prev = got;
}
// Against its own immediate neighbours, so this is a null rather than a broad scoop.
CHECK(atCorner < 1e-3 * measuredGain(fs, sr, fc * 0.95));
}
}
// The SEM's zero is AT the notch frequency, not a broadband level sag: away from the corner the
// two taps are still an equal-power pair, so the sweep holds constant power on its legs. Measured
// deep in each tap's own passband — 50 Hz for the low tap, 20 kHz for the high tap, both far from
// a 1 kHz corner — and divided by that tap's OWN analytic response there, so what is left is the
// weight the law applied. That normalization is load-bearing, not cosmetic: at Q = 0.1 a 2-pole
// approaches its passband so slowly that the pure low tap still reads 0.896 at 50 Hz, and a raw
// reading would report a 20% "sag" that is the Q, not the morph. A LINEAR crossfade would give
// 0.5 at the centre instead of 1.0, so this tolerance discriminates equal-power from linear
// decisively rather than merely confirming a plausible shape.
static void testHighNotchLowLegsHoldConstantPowerAwayFromTheNotch() {
const double sr = 48000.0, fc = 1000.0;
for (float res : {0.0f, 0.5f, 1.0f}) {
const double q = filterQFromNorm(res);
const double lowRef = analyticMag(kLowPass, 50.0, fc, q, sr);
const double highRef = analyticMag(kHighPass, 20000.0, fc, q, sr);
for (int i = 0; i <= 8; ++i) {
const float m = static_cast<float>(i) / 8.0f;
const FilterSettings fs = at(fc, res, m, 0.0f, MorphLaw::HighNotchLow);
const double low = measuredGain(fs, sr, 50.0) / lowRef;
const double high = measuredGain(fs, sr, 20000.0) / highRef;
const double power = low * low + high * high;
if (!(std::fabs(power - 1.0) <= 0.02)) {
std::printf("FAIL line %d: SEM morph %.3f res %.1f leg power %.6f (low %.6f, "
"high %.6f) — expected 1.0\n",
__LINE__, m, res, power, low, high);
++g_fail;
}
}
}
}
// Continuity as a control, not just at the corner: no step between adjacent morph positions at
// any fixed frequency, under either law. A coefficient switch at the centre — the thing an enum
// over TOPOLOGIES would have forced — shows up here as a jump. Measured off the SEM's notch
// frequency, since the null itself is a legitimate near-step in the response.
static void testMorphSweepHasNoDiscontinuity() {
const double sr = 48000.0, fc = 1000.0;
constexpr int kSteps = 40;
for (MorphLaw law : kBothLaws) {
for (float res : {0.0f, 0.5f, 1.0f}) {
for (double f : {250.0, 1000.0, 4000.0}) {
if (f == fc && law == MorphLaw::HighNotchLow) continue;
double prev = -1.0;
for (int i = 0; i <= kSteps; ++i) {
const float m = static_cast<float>(i) / kSteps;
const double got = measuredGain(at(fc, res, m, 0.0f, law), sr, f);
if (prev >= 0.0) {
// Scaled by the response's own magnitude at this setting — the passband is
// unity and the corner is Q, so below Q=1 the passband is what a step has
// to be small against, not Q.
const double scale = std::fmax(1.0, filterQFromNorm(res));
// One step is 1/40 of the travel; the steepest leg moves well under a
// tenth of that scale over one step (measured worst case is 0.03).
const double jump = std::fabs(got - prev) / scale;
if (!(jump < 0.1)) {
std::printf("FAIL line %d: %s morph %.4f res %.1f at %.0f Hz jumps "
"%.4f\n",
__LINE__, lawName(law), m, res, f, jump);
++g_fail;
}
}
prev = got;
}
}
}
}
}
// The law selects a MIX, computed once per prepare(); it must not reach the coefficient solve at
// all. Asserted bit-exactly rather than by tolerance — the cutoff, the damping term, and the
// zero-delay-loop solution are the same floats under either law, so no cutoff/Q/rate behaviour
// can differ between them by construction.
static void testMorphLawDoesNotDisturbTheCoefficients() {
for (int r = 0; r < kRateCount; ++r) {
for (int ci = 0; ci <= 8; ++ci) {
for (float res : {0.0f, 0.5f, 1.0f}) {
for (int mi = 0; mi <= 4; ++mi) {
VoiceFilter band, sem;
const float m = mi / 4.0f;
band.prepare({ci / 8.0f, res, m, 0.5f, MorphLaw::HighBandLow}, kRates[r]);
sem.prepare({ci / 8.0f, res, m, 0.5f, MorphLaw::HighNotchLow}, kRates[r]);
const SvfCoeffs& a = band.coeffs();
const SvfCoeffs& b = sem.coeffs();
CHECK(a.g == b.g && a.k == b.k);
CHECK(a.a1 == b.a1 && a.a2 == b.a2 && a.a3 == b.a3);
}
}
}
}
}
// The default is the reviewed-and-measured law, not the SEM leg. The editor and any persisted-
// state codec read this default, so a preset saved before the selector existed must still sound
// exactly as it did — asserted on the folded mix, which is the only thing the kernel sees.
static void testFilterSettingsDefaultsToTheHighBandLowLaw() {
CHECK(FilterSettings{}.morphLaw == MorphLaw::HighBandLow);
VoiceFilter defaulted, explicitLaw;
defaulted.prepare({0.5f, 0.5f, kCentre, 0.0f}, 48000.0);
explicitLaw.prepare({0.5f, 0.5f, kCentre, 0.0f, MorphLaw::HighBandLow}, 48000.0);
CHECK(defaulted.mix().m0 == explicitLaw.mix().m0);
CHECK(defaulted.mix().m1 == explicitLaw.mix().m1);
CHECK(defaulted.mix().m2 == explicitLaw.mix().m2);
}
// ---------------------------------------------------------------------------
// Drive
// ---------------------------------------------------------------------------
@@ -411,37 +411,41 @@ static float nextNoise(unsigned& rng) {
static_cast<float>(1 << 22);
}
static void checkDriveZeroBitIdentity(float morph, MorphLaw law) {
VoiceFilter f;
f.prepare(at(1000.0, 1.0f, morph, 0.0f, law), 48000.0);
f.reset();
LinearKernelRef ref0{f.coeffs(), f.mix()};
LinearKernelRef ref1{f.coeffs(), f.mix()};
unsigned rng0 = 0x13579bdfu;
for (int i = 0; i < 4096; ++i) {
const float x = nextNoise(rng0);
CHECK(f.process(0, x) == ref0.step(x));
}
// process(1, ...): channel 1's state is independent of channel 0's above.
unsigned rng1 = 0x2468acefu;
for (int i = 0; i < 4096; ++i) {
const float x = nextNoise(rng1);
CHECK(f.process(1, x) == ref1.step(x));
}
// processFrame(): both channels advanced together through the frame entry point,
// continuing from the state each channel already has.
for (int i = 0; i < 4096; ++i) {
float frame[2] = {nextNoise(rng0), nextNoise(rng1)};
const float want0 = ref0.step(frame[0]);
const float want1 = ref1.step(frame[1]);
f.processFrame(frame, 2);
CHECK(frame[0] == want0);
CHECK(frame[1] == want1);
}
}
static void testDriveZeroIsBitIdenticalToTheLinearKernel() {
for (float morph : {kHighPass, kBandPass, kLowPass}) {
VoiceFilter f;
f.prepare(at(1000.0, 1.0f, morph, 0.0f), 48000.0);
f.reset();
LinearKernelRef ref0{f.coeffs(), f.mix()};
LinearKernelRef ref1{f.coeffs(), f.mix()};
unsigned rng0 = 0x13579bdfu;
for (int i = 0; i < 4096; ++i) {
const float x = nextNoise(rng0);
CHECK(f.process(0, x) == ref0.step(x));
}
// process(1, ...): channel 1's state is independent of channel 0's above.
unsigned rng1 = 0x2468acefu;
for (int i = 0; i < 4096; ++i) {
const float x = nextNoise(rng1);
CHECK(f.process(1, x) == ref1.step(x));
}
// processFrame(): both channels advanced together through the frame entry point,
// continuing from the state each channel already has.
for (int i = 0; i < 4096; ++i) {
float frame[2] = {nextNoise(rng0), nextNoise(rng1)};
const float want0 = ref0.step(frame[0]);
const float want1 = ref1.step(frame[1]);
f.processFrame(frame, 2);
CHECK(frame[0] == want0);
CHECK(frame[1] == want1);
}
for (MorphLaw law : kBothLaws) {
for (float morph : {kHighPass, kBandPass, kLowPass}) checkDriveZeroBitIdentity(morph, law);
}
}
@@ -478,20 +482,22 @@ static void testFullDriveStaysBoundedAtEveryCutoffResonanceAndRate() {
for (int r = 0; r < kRateCount; ++r) {
const double sr = kRates[r];
for (int ci = 0; ci <= 8; ++ci) {
for (int mi = 0; mi <= 4; ++mi) {
for (float res : {0.0f, 0.5f, 1.0f}) {
VoiceFilter f;
f.prepare({ci / 8.0f, res, mi / 4.0f, 1.0f}, sr);
f.reset();
for (int i = 0; i < 4000; ++i) {
const float y = f.process(0, noise());
if (!std::isfinite(y) || std::fabs(y) > 8.0f) {
std::printf("FAIL line %d: sr=%.0f cutoff=%.2f morph=%.2f res=%.1f "
"full drive produced %g\n",
__LINE__, sr, ci / 8.0, mi / 4.0, res, y);
++g_fail;
return;
for (MorphLaw law : kBothLaws) {
for (int ci = 0; ci <= 8; ++ci) {
for (int mi = 0; mi <= 4; ++mi) {
for (float res : {0.0f, 0.5f, 1.0f}) {
VoiceFilter f;
f.prepare({ci / 8.0f, res, mi / 4.0f, 1.0f, law}, sr);
f.reset();
for (int i = 0; i < 4000; ++i) {
const float y = f.process(0, noise());
if (!std::isfinite(y) || std::fabs(y) > 8.0f) {
std::printf("FAIL line %d: %s sr=%.0f cutoff=%.2f morph=%.2f "
"res=%.1f full drive produced %g\n",
__LINE__, lawName(law), sr, ci / 8.0, mi / 4.0, res, y);
++g_fail;
return;
}
}
}
}
@@ -505,16 +511,18 @@ static void testFullDriveStaysBoundedAtEveryCutoffResonanceAndRate() {
static void testFullDriveDoesNotSelfOscillate() {
for (int r = 0; r < kRateCount; ++r) {
const double sr = kRates[r];
for (float morph : {kHighPass, kBandPass, kLowPass}) {
VoiceFilter f;
f.prepare(at(1000.0, 1.0f, morph, 1.0f), sr);
f.reset();
const int excite = static_cast<int>(sr * 0.01);
for (int i = 0; i < excite; ++i) {
f.process(0, static_cast<float>(std::sin(2.0 * kPi * 1000.0 * i / sr)));
for (MorphLaw law : kBothLaws) {
for (float morph : {kHighPass, kBandPass, kLowPass}) {
VoiceFilter f;
f.prepare(at(1000.0, 1.0f, morph, 1.0f, law), sr);
f.reset();
const int excite = static_cast<int>(sr * 0.01);
for (int i = 0; i < excite; ++i) {
f.process(0, static_cast<float>(std::sin(2.0 * kPi * 1000.0 * i / sr)));
}
for (int i = 0; i < static_cast<int>(sr * 0.5); ++i) f.process(0, 0.0f);
CHECK(f.isSilent());
}
for (int i = 0; i < static_cast<int>(sr * 0.5); ++i) f.process(0, 0.0f);
CHECK(f.isSilent());
}
}
}
@@ -621,198 +629,20 @@ static void testLowCutoffHighRateCornerHoldsTheAnalyticPeak() {
}
}
// ---------------------------------------------------------------------------
// Stability, denormals, and state
// ---------------------------------------------------------------------------
static void testFullRangeCutoffSweepAtAudioRateStaysBounded() {
unsigned rng = 0x13579bdfu;
auto noise = [&rng]() {
rng = rng * 1664525u + 1013904223u;
return static_cast<float>(static_cast<int>(rng >> 9) - (1 << 22)) /
static_cast<float>(1 << 22);
};
for (int r = 0; r < kRateCount; ++r) {
const double sr = kRates[r];
for (float morph : {kHighPass, kBandPass, kLowPass}) {
for (float res : {0.0f, 1.0f}) {
for (float drive : {0.0f, 1.0f}) {
VoiceFilter f;
f.reset();
// A fixed WALL-CLOCK sweep: the same cutoff travel per second at every rate,
// so the per-sample coefficient step gets no gentler as the rate rises.
const int n = static_cast<int>(sr * 0.25);
for (int i = 0; i < n; ++i) {
const float t = static_cast<float>(i) / static_cast<float>(n - 1);
f.prepare({t, res, morph, drive}, sr);
const float y = f.process(0, noise());
CHECK(std::isfinite(y));
CHECK(std::fabs(y) < 100.0f);
if (!std::isfinite(y)) return; // stop before the log floods
}
}
}
}
}
}
// The flush tests the ENVELOPE — both integrators — not one sample. ic1 and ic2 are in
// quadrature, so a resonator swings each through zero twice a cycle; flushing on a single one
// injects a step in phase with the resonance, which the resonance amplifies, and the filter
// limit-cycles at the floor forever instead of going quiet. Re-verified for TPT rather than
// assumed to carry over from the retired Direct Form I state.
static void testStateFlushesToZeroWithoutStallingInDenormals() {
for (int r = 0; r < kRateCount; ++r) {
const double sr = kRates[r];
// The decay to the floor is a fixed WALL-CLOCK time, so the budget scales with the rate.
const int budget = static_cast<int>(sr * 0.5);
for (float morph : {kHighPass, kBandPass, kLowPass}) {
for (float drive : {0.0f, 1.0f}) {
VoiceFilter f;
f.prepare(at(1000.0, 1.0f, morph, drive), sr);
f.reset();
// Excite, then hard-cut to silence the way a released voice does.
const int excite = static_cast<int>(sr * 0.01);
for (int i = 0; i < excite; ++i) {
f.process(0, 0.5f * static_cast<float>(std::sin(2.0 * kPi * 1000.0 * i / sr)));
}
int subnormalSamples = 0, silentAt = -1;
for (int i = 0; i < budget; ++i) {
f.process(0, 0.0f);
const VoiceFilter::State& s = f.state(0);
if ((s.ic1 != 0.0f && std::fabs(s.ic1) < FLT_MIN) ||
(s.ic2 != 0.0f && std::fabs(s.ic2) < FLT_MIN)) {
++subnormalSamples;
}
if (silentAt < 0 && f.isSilent()) silentAt = i;
}
// Without the flush the state grinds down through the subnormal range for
// thousands of samples; a stray sample or two at a zero crossing is not a stall.
CHECK(subnormalSamples <= 2);
CHECK(silentAt >= 0);
CHECK(silentAt < budget);
// And it stays silent — a flush that perturbs the loop would re-excite it.
for (int i = 0; i < 1000; ++i) CHECK(f.process(0, 0.0f) == 0.0f);
CHECK(f.isSilent());
}
}
}
}
// A high-pass under sustained DC must settle to zero and STAY there. Sampling only the final
// value is not enough: a resonator swings through zero twice a cycle, so a single late sample
// can land near zero while the envelope still rings well above it. This regressed a click train
// on the retired topology, where flushing the FIR history discarded the pinned DC and the next
// sample recomputed a full-amplitude step. TPT has no FIR history to discard, so the hazard is
// structural rather than a tuning — but the assertion is cheap and pins the outcome.
static void testHighPassSustainedDCDoesNotReRing() {
for (int r = 0; r < kRateCount; ++r) {
const double sr = kRates[r];
for (float drive : {0.0f, 1.0f}) {
VoiceFilter f;
f.prepare(at(1000.0, 1.0f, kHighPass, drive), sr);
f.reset();
const int settle = static_cast<int>(sr * 0.05);
float worstAfterSettle = 0.0f;
for (int i = 0; i < static_cast<int>(sr * 0.5); ++i) {
const float y = f.process(0, 1.0f);
if (i >= settle) worstAfterSettle = std::fmax(worstAfterSettle, std::fabs(y));
}
CHECK(worstAfterSettle < 1e-3f);
}
}
}
static void testImpulseResponseMatchesTheKernel() {
VoiceFilter f;
f.prepare(at(1000.0, 0.5f, kLowPass), 48000.0);
f.reset();
const SvfCoeffs c = f.coeffs();
// From a cleared state the first sample reduces to the coefficients alone: v1 == a2, v2 == a3.
CHECK_NEAR(f.process(0, 1.0f), c.a3, 1e-7);
VoiceFilter bp;
bp.prepare(at(1000.0, 0.5f, kBandPass), 48000.0);
bp.reset();
CHECK_NEAR(bp.process(0, 1.0f), c.a2, 1e-7);
VoiceFilter hp;
hp.prepare(at(1000.0, 0.5f, kHighPass), 48000.0);
hp.reset();
CHECK_NEAR(hp.process(0, 1.0f), 1.0 - c.k * c.a2 - c.a3, 1e-7);
}
static void testLowpassStepSettlesToUnityAndHighpassRejectsDC() {
const double sr = 48000.0;
VoiceFilter f;
f.prepare(at(1000.0, 0.0f, kLowPass), sr);
f.reset();
float y = 0.0f;
for (int i = 0; i < 48000; ++i) y = f.process(0, 1.0f);
CHECK_NEAR(y, 1.0, 1e-3); // DC passes a lowpass at unity
VoiceFilter hp;
hp.prepare(at(1000.0, 0.0f, kHighPass), sr);
hp.reset();
float worstAfterSettle = 0.0f;
for (int i = 0; i < 48000; ++i) {
y = hp.process(0, 1.0f);
if (i >= 200) worstAfterSettle = std::fmax(worstAfterSettle, std::fabs(y));
}
CHECK(worstAfterSettle < 1e-3f);
}
static void testResetClearsStateButPrepareKeepsIt() {
VoiceFilter f;
f.prepare({0.5f, 0.5f, kLowPass, 0.0f}, 48000.0);
f.process(0, 1.0f);
CHECK(!f.isSilent());
// A live parameter move must not zero the state — that is what would click.
f.prepare({0.6f, 0.5f, kLowPass, 0.0f}, 48000.0);
CHECK(!f.isSilent());
f.prepare({0.6f, 0.5f, kBandPass, 1.0f}, 48000.0);
CHECK(!f.isSilent());
f.reset();
CHECK(f.isSilent());
}
static void testChannelStateIsIndependent() {
VoiceFilter f;
f.prepare({0.5f, 0.5f, kLowPass, 0.0f}, 48000.0);
f.reset();
f.process(0, 1.0f);
CHECK(f.state(0).ic2 != 0.0f);
CHECK(f.state(1).ic2 == 0.0f);
float frame[2] = {1.0f, -1.0f};
f.processFrame(frame, 2);
CHECK(f.state(1).ic2 < 0.0f);
CHECK(frame[0] != frame[1]);
}
int main() {
testCutoffMapsThreeDecadesLogarithmically();
testCutoffNormRoundTrips();
testQSpansPointOneToTenWithRootTwoAtCenter();
testQNormRoundTrips();
testDriveDepthIsZeroAtRestAndRisesMonotonically();
testSvfCoefficientsMatchPinnedValues();
testTheSampleRateEntersOnlyThroughG();
testNonPositiveRatePrepareClearsStaleStateAndReportsSilent();
testNonPositiveRatePassesSignalThroughAtEveryMorph();
testMorphEndpointMixesAreExactlyPureTaps();
testMorphInteriorPointMatchesCosSinNotAnAlternateEqualPowerCurve();
testMorphNeverBlendsHighAgainstLowPass();
testMorphEndpointsMatchTheAnalyticTwoPoleTargets();
testCornerMagnitudeIsFlatAcrossTheWholeMorphSweep();
testCornerMagnitudeIsFlatAtQAcrossTheHighBandLowSweep();
testHighNotchLowCentreIsATrueNullAtTheCorner();
testHighNotchLowNullIsLocatedAtTheCutoff();
testHighNotchLowLegsHoldConstantPowerAwayFromTheNotch();
testMorphSweepHasNoDiscontinuity();
testMorphLawDoesNotDisturbTheCoefficients();
testFilterSettingsDefaultsToTheHighBandLowLaw();
testDriveZeroIsBitIdenticalToTheLinearKernel();
testDriveZeroResponseIsLevelInvariant();
@@ -824,14 +654,6 @@ int main() {
testResponseIsRateInvariantAtEveryMorph();
testLowCutoffHighRateCornerHoldsTheAnalyticPeak();
testFullRangeCutoffSweepAtAudioRateStaysBounded();
testStateFlushesToZeroWithoutStallingInDenormals();
testHighPassSustainedDCDoesNotReRing();
testImpulseResponseMatchesTheKernel();
testLowpassStepSettlesToUnityAndHighpassRejectsDC();
testResetClearsStateButPrepareKeepsIt();
testChannelStateIsIndependent();
if (g_fail == 0) std::printf("filter_tests: all passed\n");
else std::printf("filter_tests: %d FAILED\n", g_fail);
return g_fail == 0 ? 0 : 1;
tests/test_filter_morph.cpp
+208
View File
@@ -0,0 +1,208 @@
// Standalone tests for the pure morph domain: normalized position -> tap weights under both
// morph laws, and the fold of those weights into the kernel's three multipliers. Algebra only —
// no filter is run here. Interior expectations are derived from the intended law (in radicals,
// so they share not even a trig call with the implementation) rather than read back out of it.
// The MEASURED consequences of each law — HP-BP-LP's flat corner, HP-notch-LP's null — live in
// test_filter.cpp, where a filter is actually driven.
#include "../src/core/instrument/engine/filter/filter_morph.h"
#include "../src/core/instrument/engine/filter/filter_params.h"
#include <cmath>
#include <cstdio>
#include <initializer_list>
#include <limits>
#include <type_traits>
using namespace reasampler::instrument::engine::filter;
static int g_fail = 0;
#define CHECK(cond) do { if(!(cond)) { \
std::printf("FAIL line %d: %s\n", __LINE__, #cond); ++g_fail; } } while(0)
#define CHECK_NEAR(a, b, eps) do { const double a_ = (a), b_ = (b); \
if (!(std::fabs(a_ - b_) <= (eps))) { \
std::printf("FAIL line %d: %s (%.10f) != %s (%.10f), delta %.3e\n", \
__LINE__, #a, a_, #b, b_, std::fabs(a_ - b_)); ++g_fail; } } while(0)
static constexpr double kPi = 3.14159265358979323846;
static constexpr float kHighPass = 0.0f;
static constexpr float kCentre = 0.5f;
static constexpr float kLowPass = 1.0f;
// cos and sin of pi/8, from the half-angle identity in radicals: cos(pi/8) = sqrt((1+cos(pi/4))/2)
// with cos(pi/4) = sqrt(2)/2. No trig call, so nothing here is shared with filter_morph's cos/sin.
static double cosPi8() { return std::sqrt((1.0 + std::sqrt(2.0) / 2.0) / 2.0); } // 0.9238795325
static double sinPi8() { return std::sqrt((1.0 - std::sqrt(2.0) / 2.0) / 2.0); } // 0.3826834324
// ---------------------------------------------------------------------------
// Shared across both laws
// ---------------------------------------------------------------------------
// HighBandLow is enumerator 0 by design: a zero-initialized field, or one absent from an older
// persisted blob and left default-constructed, must land on the default law rather than the SEM
// leg. A codec written against this enum depends on that.
static void testHighBandLowIsTheZeroEnumerator() {
CHECK(static_cast<std::underlying_type_t<MorphLaw>>(MorphLaw::HighBandLow) == 0);
CHECK(MorphLaw{} == MorphLaw::HighBandLow);
}
// The endpoints are pure taps EXACTLY under BOTH laws, not to within a rounding of cos/sin — the
// laws differ only in the interior. Asserted on the folded mix, where "pure" is an exact
// statement about three floats.
static void testMorphEndpointMixesAreExactlyPureTapsUnderBothLaws() {
const float k = 1.0f / filterQFromNorm(0.5f);
for (MorphLaw law : {MorphLaw::HighBandLow, MorphLaw::HighNotchLow}) {
const MorphMix hp = morphMix(morphWeights(kHighPass, law), k);
CHECK(hp.m0 == 1.0f && hp.m1 == -k && hp.m2 == -1.0f); // v0 - k*v1 - v2
const MorphMix lp = morphMix(morphWeights(kLowPass, law), k);
CHECK(lp.m0 == 0.0f && lp.m1 == 0.0f && lp.m2 == 1.0f); // v2
// Out-of-range clamps to the endpoints rather than extrapolating.
CHECK(morphWeights(-1.0f, law).hp == 1.0f);
CHECK(morphWeights(2.0f, law).lp == 1.0f);
}
// Only the centre differs: a band-pass under one law, an HP+LP sum under the other.
const MorphMix bp = morphMix(morphWeights(kCentre, MorphLaw::HighBandLow), k);
CHECK(bp.m0 == 0.0f && bp.m1 == 1.0f && bp.m2 == 0.0f); // v1
const MorphMix notch = morphMix(morphWeights(kCentre, MorphLaw::HighNotchLow), k);
CHECK(notch.m0 != 0.0f && notch.m1 != 0.0f);
}
// NaN clamps to neither endpoint (every comparison against it is false) and lands on each law's
// degenerate — no crash, a sane fallback rather than an extrapolation. HighNotchLow has no band
// tap to fall back to, so it lands on the leg-zero endpoint instead.
static void testNaNFallsBackToASaneTapPerLaw() {
const float nan = std::numeric_limits<float>::quiet_NaN();
const MorphWeights band = morphWeights(nan, MorphLaw::HighBandLow);
CHECK(band.hp == 0.0f && band.bp == 1.0f && band.lp == 0.0f);
const MorphWeights sem = morphWeights(nan, MorphLaw::HighNotchLow);
CHECK(sem.hp == 1.0f && sem.bp == 0.0f && sem.lp == 0.0f);
}
// ---------------------------------------------------------------------------
// HighBandLow — adjacent taps only
// ---------------------------------------------------------------------------
// Pins the cos/sin curve at an interior point, not just the endpoints and the quadrature
// identity (hp^2+bp^2+lp^2=1, which any equal-power reparameterization would also satisfy).
// theta=0.5*pi*t^2 (quadratic in the leg fraction, still equal-power, still exact at both
// ends) would give hp=0.9239/bp=0.3827 here instead of the cos/sin pair's 0.7071/0.7071.
static void testHighBandLowInteriorMatchesCosSinNotAnAlternateEqualPowerCurve() {
const MorphWeights w = morphWeights(0.25f, MorphLaw::HighBandLow); // HP->BP leg, t = 0.5
const double theta = 0.5 * kPi * 0.5;
CHECK_NEAR(w.hp, std::cos(theta), 1e-6);
CHECK_NEAR(w.bp, std::sin(theta), 1e-6);
CHECK(w.lp == 0.0f);
// Each leg is half the sweep, so a leg reaches at 0.125 what the SEM's single crossfade
// reaches at 0.25 — the crispest algebraic statement of how the two laws differ.
const MorphWeights eighth = morphWeights(0.125f, MorphLaw::HighBandLow);
CHECK_NEAR(eighth.hp, cosPi8(), 1e-6);
CHECK_NEAR(eighth.bp, sinPi8(), 1e-6);
}
// HP and LP never carry weight at the same time under THIS law. That is what keeps its centre a
// band-pass: the two are antiphase at the corner and would otherwise cancel into a notch. This
// assertion is law-specific and is deliberately inverted for HighNotchLow below — do not relax
// it to cover both, which would give up the guarantee entirely.
static void testHighBandLowNeverBlendsHighAgainstLowPass() {
for (int i = 0; i <= 200; ++i) {
const MorphWeights w = morphWeights(static_cast<float>(i) / 200.0f, MorphLaw::HighBandLow);
CHECK(w.hp == 0.0f || w.lp == 0.0f);
CHECK(w.hp >= 0.0f && w.bp >= 0.0f && w.lp >= 0.0f);
// Equal power: the active pair sums in quadrature to unity.
CHECK_NEAR(w.hp * w.hp + w.bp * w.bp + w.lp * w.lp, 1.0, 1e-6);
}
}
// ---------------------------------------------------------------------------
// HighNotchLow — HP against LP, which is the whole mechanism
// ---------------------------------------------------------------------------
// The exact inverse of the HighBandLow assertion above: blending HP against LP is not a defect
// to be avoided here, it is what produces the notch. The band tap is silent throughout.
static void testHighNotchLowBlendsHighAgainstLowPassWithNoBandTap() {
for (int i = 0; i <= 200; ++i) {
const float n = static_cast<float>(i) / 200.0f;
const MorphWeights w = morphWeights(n, MorphLaw::HighNotchLow);
CHECK(w.bp == 0.0f);
CHECK(w.hp >= 0.0f && w.lp >= 0.0f);
// Both taps carry weight everywhere strictly between the endpoints.
if (i > 0 && i < 200) CHECK(w.hp > 0.0f && w.lp > 0.0f);
// Equal power, which is what keeps the legs from sagging away from the notch frequency.
CHECK_NEAR(w.hp * w.hp + w.lp * w.lp, 1.0, 1e-6);
}
}
// Pins the single equal-power crossfade at interior points against radical-derived values, so a
// law that still hits both endpoints but bends differently between them fails. Discriminators at
// n=0.25: a LINEAR crossfade gives 0.75/0.25; a two-leg construction (HighBandLow's spacing
// applied to an HP/LP pair) gives 0.7071/0.7071. Both are far outside this tolerance.
static void testHighNotchLowInteriorWeightsMatchTheSingleEqualPowerCrossfade() {
// cos/sin of pi/8 and 3pi/8; the latter pair is the former swapped.
const double c8 = cosPi8(), s8 = sinPi8();
CHECK_NEAR(c8, 0.9238795325112867, 1e-15);
CHECK_NEAR(s8, 0.3826834323650898, 1e-15);
const MorphWeights quarter = morphWeights(0.25f, MorphLaw::HighNotchLow);
CHECK_NEAR(quarter.hp, c8, 1e-6);
CHECK_NEAR(quarter.lp, s8, 1e-6);
const MorphWeights threeQuarters = morphWeights(0.75f, MorphLaw::HighNotchLow);
CHECK_NEAR(threeQuarters.hp, s8, 1e-6);
CHECK_NEAR(threeQuarters.lp, c8, 1e-6);
const MorphWeights centre = morphWeights(kCentre, MorphLaw::HighNotchLow);
CHECK_NEAR(centre.hp, std::sqrt(2.0) / 2.0, 1e-6);
CHECK_NEAR(centre.lp, std::sqrt(2.0) / 2.0, 1e-6);
// Symmetric about the centre, so the sweep reads the same in either direction.
for (int i = 0; i <= 100; ++i) {
const float n = static_cast<float>(i) / 100.0f;
const MorphWeights a = morphWeights(n, MorphLaw::HighNotchLow);
const MorphWeights b = morphWeights(1.0f - n, MorphLaw::HighNotchLow);
CHECK_NEAR(a.hp, b.lp, 1e-6);
}
}
// The centre's cancellation is STRUCTURAL, not a runtime near-miss of two large numbers. The fold
// is m2 = lp - hp, and at the centre the two weights are the same float — cos and sin of pi/4
// differ by about an ulp of DOUBLE, ~1e-16, which is nine orders below float's ~6e-8 spacing
// there, so they round to one value. m2 is therefore exactly 0 and the output reduces to
// hp*(x - k*v1): the high and low taps cannot drift apart by a rounding.
static void testHighNotchLowCentreFoldsToAnExactlyCancellingMix() {
for (float res : {0.0f, 0.5f, 1.0f}) {
const float k = 1.0f / filterQFromNorm(res);
const MorphWeights w = morphWeights(kCentre, MorphLaw::HighNotchLow);
CHECK(w.hp == w.lp);
const MorphMix m = morphMix(w, k);
CHECK(m.m2 == 0.0f);
CHECK(m.m0 == w.hp);
CHECK(m.m1 == -w.hp * k);
}
}
int main() {
testHighBandLowIsTheZeroEnumerator();
testMorphEndpointMixesAreExactlyPureTapsUnderBothLaws();
testNaNFallsBackToASaneTapPerLaw();
testHighBandLowInteriorMatchesCosSinNotAnAlternateEqualPowerCurve();
testHighBandLowNeverBlendsHighAgainstLowPass();
testHighNotchLowBlendsHighAgainstLowPassWithNoBandTap();
testHighNotchLowInteriorWeightsMatchTheSingleEqualPowerCrossfade();
testHighNotchLowCentreFoldsToAnExactlyCancellingMix();
if (g_fail == 0) std::printf("filter_morph_tests: all passed\n");
else std::printf("filter_morph_tests: %d FAILED\n", g_fail);
return g_fail == 0 ? 0 : 1;
}
tests/test_filter_params.cpp
+121
View File
@@ -0,0 +1,121 @@
// Standalone tests for the filter's control domain — normalized knob position to cutoff Hz, Q,
// and drive depth, plus the exact inverses. No DSP is run here and no sample rate appears, which
// is the point: filter_params is deliberately rate-free. Interior points are pinned against a
// derivation of the intended law written out in-test, so a curve that still hits the anchors but
// bends differently between them fails.
#include "../src/core/instrument/engine/filter/filter_params.h"
#include <cmath>
#include <cstdio>
using namespace reasampler::instrument::engine::filter;
static int g_fail = 0;
#define CHECK(cond) do { if(!(cond)) { \
std::printf("FAIL line %d: %s\n", __LINE__, #cond); ++g_fail; } } while(0)
#define CHECK_NEAR(a, b, eps) do { const double a_ = (a), b_ = (b); \
if (!(std::fabs(a_ - b_) <= (eps))) { \
std::printf("FAIL line %d: %s (%.10f) != %s (%.10f), delta %.3e\n", \
__LINE__, #a, a_, #b, b_, std::fabs(a_ - b_)); ++g_fail; } } while(0)
static void testCutoffMapsThreeDecadesLogarithmically() {
CHECK_NEAR(filterCutoffHzFromNorm(0.0f), 20.0, 1e-3);
CHECK_NEAR(filterCutoffHzFromNorm(1.0f), 20000.0, 1e-2);
// Exactly three decades, so the decade midpoints land on round numbers.
CHECK_NEAR(filterCutoffHzFromNorm(1.0f / 3.0f), 200.0, 1e-3);
CHECK_NEAR(filterCutoffHzFromNorm(2.0f / 3.0f), 2000.0, 1e-2);
// Half-decade steps confirm the sweep is log, not linear.
CHECK_NEAR(filterCutoffHzFromNorm(1.0f / 6.0f), 20.0 * std::sqrt(10.0), 1e-3);
CHECK_NEAR(filterCutoffHzFromNorm(0.5f), 20.0 * std::sqrt(1000.0), 1e-2);
CHECK_NEAR(filterCutoffHzFromNorm(-1.0f), 20.0, 1e-3);
CHECK_NEAR(filterCutoffHzFromNorm(2.0f), 20000.0, 1e-2);
}
static void testCutoffNormRoundTrips() {
for (int i = 0; i <= 20; ++i) {
const float n = static_cast<float>(i) / 20.0f;
CHECK_NEAR(filterNormFromCutoffHz(filterCutoffHzFromNorm(n)), n, 1e-6);
}
CHECK_NEAR(filterNormFromCutoffHz(200.0f), 1.0 / 3.0, 1e-6);
CHECK(filterNormFromCutoffHz(1.0f) == 0.0f);
CHECK(filterNormFromCutoffHz(48000.0f) == 1.0f);
}
static void testQSpansPointOneToTenWithRootTwoAtCenter() {
CHECK_NEAR(filterQFromNorm(0.0f), 0.1, 1e-6);
CHECK_NEAR(filterQFromNorm(0.5f), std::sqrt(2.0), 1e-5);
CHECK_NEAR(filterQFromNorm(1.0f), 10.0, 1e-4);
CHECK_NEAR(filterQFromNorm(-1.0f), 0.1, 1e-6);
CHECK_NEAR(filterQFromNorm(2.0f), 10.0, 1e-4);
// Pins the single quadratic-in-log-Q curve at two interior points, derived independently by
// solving log Q = a + b*n + c*n^2 through the three anchors above rather than read out of
// the implementation. A two-spliced-log-segments curve (log-linear on each half, the design
// this module doc explicitly rejects for its center-detent slope kink) would give 0.376 and
// 3.761 here instead — both comfortably outside this tolerance.
{
const double lo = std::log(static_cast<double>(kFilterQMin));
const double mid = std::log(static_cast<double>(kFilterQCenter));
const double hi = std::log(static_cast<double>(kFilterQMax));
const double c = 2.0 * lo + 2.0 * hi - 4.0 * mid;
const double b = hi - lo - c;
const double a = lo;
auto qLaw = [&](double n) { return std::exp(a + b * n + c * n * n); };
CHECK_NEAR(filterQFromNorm(0.25f), qLaw(0.25), 1e-5);
CHECK_NEAR(filterQFromNorm(0.75f), qLaw(0.75), 1e-5);
}
// Strictly monotonic across the whole travel — no fold-back from the quadratic term.
float prev = -1.0f;
for (int i = 0; i <= 1000; ++i) {
const float q = filterQFromNorm(static_cast<float>(i) / 1000.0f);
CHECK(q > prev);
prev = q;
}
}
static void testQNormRoundTrips() {
for (int i = 0; i <= 20; ++i) {
const float n = static_cast<float>(i) / 20.0f;
CHECK_NEAR(filterNormFromQ(filterQFromNorm(n)), n, 1e-5);
}
CHECK_NEAR(filterNormFromQ(static_cast<float>(std::sqrt(2.0))), 0.5, 1e-5);
CHECK(filterNormFromQ(0.0f) == 0.0f);
CHECK(filterNormFromQ(1000.0f) == 1.0f);
}
static void testDriveDepthIsZeroAtRestAndRisesMonotonically() {
// Exactly zero, not nearly: the limiter is the identity only at depth 0.
CHECK(filterDriveDepthFromNorm(0.0f) == 0.0f);
CHECK(filterDriveDepthFromNorm(-1.0f) == 0.0f);
CHECK_NEAR(filterDriveDepthFromNorm(1.0f), kFilterDriveDepthMax, 1e-6);
CHECK_NEAR(filterDriveDepthFromNorm(2.0f), kFilterDriveDepthMax, 1e-6);
// Pins the SQUARE law at an interior point, not just the anchors: a linear law would give
// kFilterDriveDepthMax/2 (2.0) here, not kFilterDriveDepthMax/4 (1.0).
CHECK_NEAR(filterDriveDepthFromNorm(0.5f), kFilterDriveDepthMax * 0.25, 1e-6);
float prev = -1.0f;
for (int i = 0; i <= 100; ++i) {
const float d = filterDriveDepthFromNorm(static_cast<float>(i) / 100.0f);
CHECK(d > prev);
prev = d;
}
}
int main() {
testCutoffMapsThreeDecadesLogarithmically();
testCutoffNormRoundTrips();
testQSpansPointOneToTenWithRootTwoAtCenter();
testQNormRoundTrips();
testDriveDepthIsZeroAtRestAndRisesMonotonically();
if (g_fail == 0) std::printf("filter_params_tests: all passed\n");
else std::printf("filter_params_tests: %d FAILED\n", g_fail);
return g_fail == 0 ? 0 : 1;
}
tests/test_filter_state.cpp
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// Standalone tests for the running filter's NUMERICAL behaviour and state lifecycle — bounded
// output under a live parameter sweep, the denormal flush, DC handling, the impulse response
// against the coefficients, and reset/prepare/per-channel state rules. Split from test_filter.cpp
// along the one seam that costs nothing: none of these need the frequency-response measurement
// harness, so the analytic reference lives in exactly one file and cannot fork.
#include "../src/core/instrument/engine/filter/filter_coeffs.h"
#include "../src/core/instrument/engine/filter/filter_morph.h"
#include "../src/core/instrument/engine/filter/filter_params.h"
#include "../src/core/instrument/engine/filter/voice_filter.h"
#include <cfloat>
#include <cmath>
#include <cstdio>
#include <initializer_list>
using namespace reasampler::instrument::engine::filter;
static int g_fail = 0;
#define CHECK(cond) do { if(!(cond)) { \
std::printf("FAIL line %d: %s\n", __LINE__, #cond); ++g_fail; } } while(0)
#define CHECK_NEAR(a, b, eps) do { const double a_ = (a), b_ = (b); \
if (!(std::fabs(a_ - b_) <= (eps))) { \
std::printf("FAIL line %d: %s (%.10f) != %s (%.10f), delta %.3e\n", \
__LINE__, #a, a_, #b, b_, std::fabs(a_ - b_)); ++g_fail; } } while(0)
static constexpr double kPi = 3.14159265358979323846;
static constexpr float kHighPass = 0.0f;
static constexpr float kBandPass = 0.5f;
static constexpr float kCentre = 0.5f;
static constexpr float kLowPass = 1.0f;
static const MorphLaw kBothLaws[] = {MorphLaw::HighBandLow, MorphLaw::HighNotchLow};
// The rates the invariance claims are made over.
static const double kRates[] = {44100.0, 48000.0, 88200.0, 96000.0, 192000.0};
static constexpr int kRateCount = 5;
static FilterSettings at(double fcHz, float res, float morph, float drive = 0.0f,
MorphLaw law = MorphLaw::HighBandLow) {
return {filterNormFromCutoffHz(static_cast<float>(fcHz)), res, morph, drive, law};
}
static void testFullRangeCutoffSweepAtAudioRateStaysBounded() {
unsigned rng = 0x13579bdfu;
auto noise = [&rng]() {
rng = rng * 1664525u + 1013904223u;
return static_cast<float>(static_cast<int>(rng >> 9) - (1 << 22)) /
static_cast<float>(1 << 22);
};
for (int r = 0; r < kRateCount; ++r) {
const double sr = kRates[r];
for (MorphLaw law : kBothLaws) {
for (float morph : {kHighPass, kBandPass, kLowPass}) {
for (float res : {0.0f, 1.0f}) {
for (float drive : {0.0f, 1.0f}) {
VoiceFilter f;
f.reset();
// A fixed WALL-CLOCK sweep: the same cutoff travel per second at every
// rate, so the per-sample coefficient step gets no gentler as the rate
// rises.
const int n = static_cast<int>(sr * 0.25);
for (int i = 0; i < n; ++i) {
const float t = static_cast<float>(i) / static_cast<float>(n - 1);
f.prepare({t, res, morph, drive, law}, sr);
const float y = f.process(0, noise());
CHECK(std::isfinite(y));
CHECK(std::fabs(y) < 100.0f);
if (!std::isfinite(y)) return; // stop before the log floods
}
}
}
}
}
}
}
// The flush tests the ENVELOPE — both integrators — not one sample. ic1 and ic2 are in
// quadrature, so a resonator swings each through zero twice a cycle; flushing on a single one
// injects a step in phase with the resonance, which the resonance amplifies, and the filter
// limit-cycles at the floor forever instead of going quiet. Re-verified for TPT rather than
// assumed to carry over from the retired Direct Form I state.
static void checkFlushGoesSilent(double sr, float morph, float drive, MorphLaw law) {
// The decay to the floor is a fixed WALL-CLOCK time, so the budget scales with the rate.
const int budget = static_cast<int>(sr * 0.5);
VoiceFilter f;
f.prepare(at(1000.0, 1.0f, morph, drive, law), sr);
f.reset();
// Excite, then hard-cut to silence the way a released voice does.
const int excite = static_cast<int>(sr * 0.01);
for (int i = 0; i < excite; ++i) {
f.process(0, 0.5f * static_cast<float>(std::sin(2.0 * kPi * 1000.0 * i / sr)));
}
int subnormalSamples = 0, silentAt = -1;
for (int i = 0; i < budget; ++i) {
f.process(0, 0.0f);
const VoiceFilter::State& s = f.state(0);
if ((s.ic1 != 0.0f && std::fabs(s.ic1) < FLT_MIN) ||
(s.ic2 != 0.0f && std::fabs(s.ic2) < FLT_MIN)) {
++subnormalSamples;
}
if (silentAt < 0 && f.isSilent()) silentAt = i;
}
// Without the flush the state grinds down through the subnormal range for thousands of
// samples; a stray sample or two at a zero crossing is not a stall.
CHECK(subnormalSamples <= 2);
CHECK(silentAt >= 0);
CHECK(silentAt < budget);
// And it stays silent — a flush that perturbs the loop would re-excite it.
for (int i = 0; i < 1000; ++i) CHECK(f.process(0, 0.0f) == 0.0f);
CHECK(f.isSilent());
}
static void testStateFlushesToZeroWithoutStallingInDenormals() {
for (int r = 0; r < kRateCount; ++r) {
for (MorphLaw law : kBothLaws) {
for (float morph : {kHighPass, kBandPass, kLowPass}) {
for (float drive : {0.0f, 1.0f}) checkFlushGoesSilent(kRates[r], morph, drive, law);
}
}
}
}
// A high-pass under sustained DC must settle to zero and STAY there. Sampling only the final
// value is not enough: a resonator swings through zero twice a cycle, so a single late sample
// can land near zero while the envelope still rings well above it. This regressed a click train
// on the retired topology, where flushing the FIR history discarded the pinned DC and the next
// sample recomputed a full-amplitude step. TPT has no FIR history to discard, so the hazard is
// structural rather than a tuning — but the assertion is cheap and pins the outcome. Morph 0 is
// the same pure high-pass under either law, so this needs no law loop.
static void testHighPassSustainedDCDoesNotReRing() {
for (int r = 0; r < kRateCount; ++r) {
const double sr = kRates[r];
for (float drive : {0.0f, 1.0f}) {
VoiceFilter f;
f.prepare(at(1000.0, 1.0f, kHighPass, drive), sr);
f.reset();
const int settle = static_cast<int>(sr * 0.05);
float worstAfterSettle = 0.0f;
for (int i = 0; i < static_cast<int>(sr * 0.5); ++i) {
const float y = f.process(0, 1.0f);
if (i >= settle) worstAfterSettle = std::fmax(worstAfterSettle, std::fabs(y));
}
CHECK(worstAfterSettle < 1e-3f);
}
}
}
static void testImpulseResponseMatchesTheKernel() {
VoiceFilter f;
f.prepare(at(1000.0, 0.5f, kLowPass), 48000.0);
f.reset();
const SvfCoeffs c = f.coeffs();
// From a cleared state the first sample reduces to the coefficients alone: v1 == a2, v2 == a3.
CHECK_NEAR(f.process(0, 1.0f), c.a3, 1e-7);
VoiceFilter bp;
bp.prepare(at(1000.0, 0.5f, kBandPass), 48000.0);
bp.reset();
CHECK_NEAR(bp.process(0, 1.0f), c.a2, 1e-7);
VoiceFilter hp;
hp.prepare(at(1000.0, 0.5f, kHighPass), 48000.0);
hp.reset();
CHECK_NEAR(hp.process(0, 1.0f), 1.0 - c.k * c.a2 - c.a3, 1e-7);
// Under HighNotchLow the centre's first sample is the SUM of the high and low taps, scaled by
// the shared weight — the same algebra the null rests on, seen one sample in.
VoiceFilter sem;
sem.prepare(at(1000.0, 0.5f, kCentre, 0.0f, MorphLaw::HighNotchLow), 48000.0);
sem.reset();
const double w = morphWeights(kCentre, MorphLaw::HighNotchLow).hp;
const double highTap = 1.0 - c.k * c.a2 - c.a3;
const double lowTap = c.a3;
CHECK_NEAR(sem.process(0, 1.0f), w * (highTap + lowTap), 1e-6);
}
static void testLowpassStepSettlesToUnityAndHighpassRejectsDC() {
const double sr = 48000.0;
VoiceFilter f;
f.prepare(at(1000.0, 0.0f, kLowPass), sr);
f.reset();
float y = 0.0f;
for (int i = 0; i < 48000; ++i) y = f.process(0, 1.0f);
CHECK_NEAR(y, 1.0, 1e-3); // DC passes a lowpass at unity
VoiceFilter hp;
hp.prepare(at(1000.0, 0.0f, kHighPass), sr);
hp.reset();
float worstAfterSettle = 0.0f;
for (int i = 0; i < 48000; ++i) {
y = hp.process(0, 1.0f);
if (i >= 200) worstAfterSettle = std::fmax(worstAfterSettle, std::fabs(y));
}
CHECK(worstAfterSettle < 1e-3f);
}
static void testResetClearsStateButPrepareKeepsIt() {
VoiceFilter f;
f.prepare({0.5f, 0.5f, kLowPass, 0.0f}, 48000.0);
f.process(0, 1.0f);
CHECK(!f.isSilent());
// A live parameter move must not zero the state — that is what would click. Switching the
// morph law is a parameter move like any other: it only recomputes the mix.
f.prepare({0.6f, 0.5f, kLowPass, 0.0f}, 48000.0);
CHECK(!f.isSilent());
f.prepare({0.6f, 0.5f, kBandPass, 1.0f}, 48000.0);
CHECK(!f.isSilent());
f.prepare({0.6f, 0.5f, kCentre, 1.0f, MorphLaw::HighNotchLow}, 48000.0);
CHECK(!f.isSilent());
f.reset();
CHECK(f.isSilent());
}
static void testChannelStateIsIndependent() {
VoiceFilter f;
f.prepare({0.5f, 0.5f, kLowPass, 0.0f}, 48000.0);
f.reset();
f.process(0, 1.0f);
CHECK(f.state(0).ic2 != 0.0f);
CHECK(f.state(1).ic2 == 0.0f);
float frame[2] = {1.0f, -1.0f};
f.processFrame(frame, 2);
CHECK(f.state(1).ic2 < 0.0f);
CHECK(frame[0] != frame[1]);
}
int main() {
testFullRangeCutoffSweepAtAudioRateStaysBounded();
testStateFlushesToZeroWithoutStallingInDenormals();
testHighPassSustainedDCDoesNotReRing();
testImpulseResponseMatchesTheKernel();
testLowpassStepSettlesToUnityAndHighpassRejectsDC();
testResetClearsStateButPrepareKeepsIt();
testChannelStateIsIndependent();
if (g_fail == 0) std::printf("filter_state_tests: all passed\n");
else std::printf("filter_state_tests: %d FAILED\n", g_fail);
return g_fail == 0 ? 0 : 1;
}