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Merged
baconpaul merged 1 commit into from
May 9, 2026
Merged

Add LFSR Noise Source #365

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39 changes: 36 additions & 3 deletions src/dsp/noise_helper.h
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,13 @@ namespace baconpaul::six_sines
struct NoiseHelper
{
using NoiseType = Patch::SourceNode::NoiseType;
using LFSRMode = Patch::SourceNode::LFSRMode;

// This wierd constant is roughly the frequency at which the thing would turn over at 48khz in
// a CPU running at 1.789 mhz and a cycle length of 96 cpu cycles.
static constexpr float lfsrFreeReferenceHz{1.789 * 1000000 / 48000 * 96};

static constexpr float lfsrTuningRange{12.f};

// Tilt filter takes ±tiltMaxDb across the bipolar N range.
static constexpr float tiltMaxDb{6.f};
Expand All @@ -48,11 +55,17 @@ struct NoiseHelper
sst::filters::FastTiltNoiseFilter<Host> tiltFilter;
sst::basic_blocks::dsp::RNG &rng;

// 15-bit Galois LFSR shared by both chip modes. Seeded non-zero per helper
// so simultaneous voices don't lock-step.
uint16_t lfsrReg{0x0001};
double lfsrPhaseAcc{0.0};

NoiseHelper(sst::basic_blocks::dsp::RNG &r,
const sst::basic_blocks::tables::DbToLinearProvider &dbProv)
: pinkNoise(r.unifU32()), tiltFilter(host), rng(r)
{
host.db = &dbProv;
lfsrReg = static_cast<uint16_t>((r.unifU32() & 0x7FFFu) | 0x0001u);
}

void setSampleRate(double sr) { host.sri = 1.0 / sr; }
Expand All @@ -70,8 +83,9 @@ struct NoiseHelper
}

// Refill 16 samples of the chosen noise color into buf, normalized to ~±1.
// CHIP_LFSR is silent for now until the LFSR generator lands.
void fill16(float buf[16], NoiseType type, float nValue)
// baseFreq drives the LFSR shift clock when the mode is keytracked; otherwise
// a fixed reference (lfsrFreeReferenceHz) is used.
void fill16(float buf[16], NoiseType type, float nValue, float baseFreq, LFSRMode lfsrMode)
{
switch (type)
{
Expand All @@ -98,10 +112,29 @@ struct NoiseHelper
break;
}
case NoiseType::CHIP_LFSR:
{
const bool isShort =
(lfsrMode == LFSRMode::SHORT || lfsrMode == LFSRMode::SHORT_KEYTRACK);
const bool keytrack =
(lfsrMode == LFSRMode::SHORT_KEYTRACK || lfsrMode == LFSRMode::LONG_KEYTRACK);
const int xorBit = isShort ? 6 : 1;
const float refFreq = (keytrack ? baseFreq : 261.62) * lfsrFreeReferenceHz / 261.62;
const float shiftFreq = refFreq * std::exp2((nValue - 0.5f) * lfsrTuningRange);
const double dPhase = static_cast<double>(shiftFreq) * host.sri;
for (int i = 0; i < 16; ++i)
buf[i] = 0.f;
{
lfsrPhaseAcc += dPhase;
while (lfsrPhaseAcc >= 1.0)
{
uint16_t fb = ((lfsrReg >> 0) ^ (lfsrReg >> xorBit)) & 1u;
lfsrReg = static_cast<uint16_t>((lfsrReg >> 1) | (fb << 14));
lfsrPhaseAcc -= 1.0;
}
buf[i] = (lfsrReg & 1u) ? 1.f : -1.f;
}
break;
}
}
}
};
} // namespace baconpaul::six_sines
Expand Down
6 changes: 5 additions & 1 deletion src/dsp/op_source.h
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Expand Up @@ -493,9 +493,11 @@ struct alignas(16) OpSource : public EnvelopeSupport<Patch::SourceNode>,
using EM = Patch::SourceNode::ExtendedMode;
using NMode = Patch::SourceNode::NoiseMode;
using NT = Patch::SourceNode::NoiseType;
using LM = Patch::SourceNode::LFSRMode;
float nextM{0.f}, dM{0.f};
float nextN{0.f};
NT noiseType{NT::PINK};
LM lfsrMode{LM::LONG_KEYTRACK};
if constexpr (ET == EM::PHASE_REMAP || ET == EM::RESONANT_SWEEP || ET == EM::NOISE)
{
// Raw target m for this block: patch value + external mod + env / lfo contributions.
Expand Down Expand Up @@ -523,6 +525,8 @@ struct alignas(16) OpSource : public EnvelopeSupport<Patch::SourceNode>,
nextN = extendedLagN.v;
noiseType =
static_cast<NT>(static_cast<uint32_t>(std::round(sourceNode.noiseType.value)));
lfsrMode =
static_cast<LM>(static_cast<uint32_t>(std::round(sourceNode.lfsrMode.value)));
}

for (int i = 0; i < blockSize; ++i)
Expand Down Expand Up @@ -587,7 +591,7 @@ struct alignas(16) OpSource : public EnvelopeSupport<Patch::SourceNode>,
{
if (noisePos >= 16)
{
noiseHelper.fill16(noiseBuf, noiseType, nextN);
noiseHelper.fill16(noiseBuf, noiseType, nextN, baseFrequency, lfsrMode);
noisePos = 0;
}
float noise = noiseBuf[noisePos++];
Expand Down
27 changes: 25 additions & 2 deletions src/synth/patch.h
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Original file line number Diff line number Diff line change
Expand Up @@ -544,6 +544,14 @@ struct Patch : pats::PatchBase<Patch, Param>
CHIP_LFSR = 3,
};

enum struct LFSRMode : uint32_t
{
SHORT = 0,
SHORT_KEYTRACK = 1,
LONG = 2,
LONG_KEYTRACK = 3,
};

// Noise samples come out of NoiseHelper normalized to ~±1. ADD_TO_PHASE
// attenuates further since one full cycle of phase jitter is too much.
static constexpr float noisePhaseScale = 0.33f;
Expand Down Expand Up @@ -761,6 +769,7 @@ struct Patch : pats::PatchBase<Patch, Param>
.withID(id(176, idx))),
extendedModeN(floatMd(version_120b)
.asPercent()
.withPolarity(md_t::Polarity::BIPOLAR)
.withName(name(idx) + " Extended Mode N")
.withGroupName(name(idx))
.withDefault(0.5f)
Expand Down Expand Up @@ -854,7 +863,19 @@ struct Patch : pats::PatchBase<Patch, Param>
{(int)NoiseType::PINK, "Pink"},
{(int)NoiseType::TILT, "Tilt"},
{(int)NoiseType::CHIP_LFSR, "Chip LFSR"},
}))
})),
lfsrMode(intMd(version_120f)
.withRange(0, 3)
.withDefault((int)LFSRMode::LONG_KEYTRACK)
.withID(id(187, idx))
.withName(name(idx) + " LFSR Mode")
.withGroupName(name(idx))
.withUnorderedMapFormatting({
{(int)LFSRMode::SHORT, "Short"},
{(int)LFSRMode::SHORT_KEYTRACK, "Short Keytrack"},
{(int)LFSRMode::LONG, "Long"},
{(int)LFSRMode::LONG_KEYTRACK, "Long Keytrack"},
}))

{
index = idx;
Expand Down Expand Up @@ -899,6 +920,7 @@ struct Patch : pats::PatchBase<Patch, Param>
Param resonantSweepFrequencyDepth;
Param noiseMode;
Param noiseType;
Param lfsrMode;

std::array<Param, numModsPer> modtarget;

Expand Down Expand Up @@ -931,7 +953,8 @@ struct Patch : pats::PatchBase<Patch, Param>
&resonantSweepWindowShape,
&resonantSweepFrequencyDepth,
&noiseMode,
&noiseType};
&noiseType,
&lfsrMode};
for (int i = 0; i < numModsPer; ++i)
res.push_back(&modtarget[i]);
appendDAHDSRParams(res);
Expand Down
40 changes: 33 additions & 7 deletions src/ui/source-sub-panel.cpp
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Expand Up @@ -410,7 +410,7 @@ struct ResSweepPlotter : juce::Component
*/
struct NoisePainter : juce::Component
{
const Param &wf, &ph, &mp, &np, &noiseMode, &noiseType;
const Param &wf, &ph, &mp, &np, &noiseMode, &noiseType, &lfsrMode;
SixSinesEditor &editor;
SinTable st;

Expand All @@ -431,8 +431,9 @@ struct NoisePainter : juce::Component
}

NoisePainter(const Param &w, const Param &p, const Param &mParam, const Param &nParam,
const Param &nMode, const Param &nType, SixSinesEditor &e)
: wf(w), ph(p), mp(mParam), np(nParam), noiseMode(nMode), noiseType(nType), editor(e)
const Param &nMode, const Param &nType, const Param &lMode, SixSinesEditor &e)
: wf(w), ph(p), mp(mParam), np(nParam), noiseMode(nMode), noiseType(nType), lfsrMode(lMode),
editor(e)
{
}

Expand Down Expand Up @@ -473,8 +474,10 @@ struct NoisePainter : juce::Component

using NM = Patch::SourceNode::NoiseMode;
using NT = Patch::SourceNode::NoiseType;
using LM = Patch::SourceNode::LFSRMode;
const auto nm = static_cast<NM>(static_cast<uint32_t>(std::round(noiseMode.value)));
const auto nt = static_cast<NT>(static_cast<uint32_t>(std::round(noiseType.value)));
const auto lm = static_cast<LM>(static_cast<uint32_t>(std::round(lfsrMode.value)));
const float m = mp.value;
const float nVal = np.value;

Expand Down Expand Up @@ -506,7 +509,7 @@ struct NoisePainter : juce::Component

if (noisePos >= 16)
{
helper.fill16(noiseBuf, nt, nVal);
helper.fill16(noiseBuf, nt, nVal, 220.f, lm);
noisePos = 0;
}
float n = noiseBuf[noisePos++];
Expand Down Expand Up @@ -828,9 +831,16 @@ void SourceSubPanel::setSelectedIndex(size_t idx)
noiseTypeL->setText("Type");
addChildComponent(*noiseTypeL);

noisePainter =
std::make_unique<NoisePainter>(sn.waveForm, sn.startingPhase, sn.extendedModeM,
sn.extendedModeN, sn.noiseMode, sn.noiseType, editor);
createComponent(editor, *this, sn.lfsrMode, lfsrMode, lfsrModeD);
addChildComponent(*lfsrMode);
traverse(lfsrMode);
lfsrModeL = std::make_unique<jcmp::Label>();
lfsrModeL->setText("LFSR");
addChildComponent(*lfsrModeL);

noisePainter = std::make_unique<NoisePainter>(sn.waveForm, sn.startingPhase, sn.extendedModeM,
sn.extendedModeN, sn.noiseMode, sn.noiseType,
sn.lfsrMode, editor);
addChildComponent(*noisePainter);

// Live-repaint extended-mode painters when any of their inputs change.
Expand All @@ -855,18 +865,22 @@ void SourceSubPanel::setSelectedIndex(size_t idx)
{
if (!w)
return;
w->setExtendedModeVisibility();
w->setEnabledState();
w->resized();
if (w->noisePainter)
w->noisePainter->repaint();
};
noiseTypeD->onGuiSetValue = noiseTypeChanged;
lfsrModeD->onGuiSetValue = repaintExt;
editor.componentRefreshByID[sn.extendedModeM.meta.id] = repaintExt;
editor.componentRefreshByID[sn.extendedModeN.meta.id] = repaintExt;
editor.componentRefreshByID[sn.phaseMapModeShape.meta.id] = repaintExt;
editor.componentRefreshByID[sn.resonantSweepWindowShape.meta.id] = repaintExt;
editor.componentRefreshByID[sn.resonantSweepFrequencyDepth.meta.id] = repaintExt;
editor.componentRefreshByID[sn.noiseMode.meta.id] = repaintExt;
editor.componentRefreshByID[sn.noiseType.meta.id] = noiseTypeChanged;
editor.componentRefreshByID[sn.lfsrMode.meta.id] = repaintExt;

setExtendedModeVisibility();

Expand Down Expand Up @@ -1118,6 +1132,7 @@ void SourceSubPanel::resized()
auto leftStack = jlo::VList().withAutoGap(uicMargin);
leftStack.add(labelJogRow(*noiseModeL, *noiseMode));
leftStack.add(labelJogRow(*noiseTypeL, *noiseType));
leftStack.add(labelJogRow(*lfsrModeL, *lfsrMode));
auto leftCol = jlo::VList().withWidth(leftColW);
leftCol.add(leftStack.centerInParent());
topLo.add(leftCol);
Expand Down Expand Up @@ -1184,6 +1199,15 @@ void SourceSubPanel::setExtendedModeVisibility()
noiseTypeL->setVisible(isNoise);
if (noisePainter)
noisePainter->setVisible(isNoise);

using NT = Patch::SourceNode::NoiseType;
auto &sn = editor.patchCopy.sourceNodes[index];
auto nt = static_cast<NT>(static_cast<int>(std::round(sn.noiseType.value)));
auto showLfsr = isNoise && (nt == NT::CHIP_LFSR);
if (lfsrMode)
lfsrMode->setVisible(showLfsr);
if (lfsrModeL)
lfsrModeL->setVisible(showLfsr);
}

void SourceSubPanel::setEnabledState()
Expand Down Expand Up @@ -1239,6 +1263,8 @@ void SourceSubPanel::setEnabledState()
noiseMode->setEnabled(!isAudioIn);
if (noiseType)
noiseType->setEnabled(!isAudioIn);
if (lfsrMode)
lfsrMode->setEnabled(!isAudioIn);

using NT = Patch::SourceNode::NoiseType;
auto nt = static_cast<NT>(static_cast<int>(std::round(sn.noiseType.value)));
Expand Down
3 changes: 3 additions & 0 deletions src/ui/source-sub-panel.h
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Expand Up @@ -110,6 +110,9 @@ struct SourceSubPanel : juce::Component,
std::unique_ptr<jcmp::JogUpDownButton> noiseType;
std::unique_ptr<PatchDiscrete> noiseTypeD;
std::unique_ptr<jcmp::Label> noiseTypeL;
std::unique_ptr<jcmp::JogUpDownButton> lfsrMode;
std::unique_ptr<PatchDiscrete> lfsrModeD;
std::unique_ptr<jcmp::Label> lfsrModeL;
std::unique_ptr<juce::Component> noisePainter;

void setExtendedModeVisibility();
Expand Down
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