Initial effects

src/CMakeLists.txt

@@ -15,6 +15,9 @@ set (SFIZZ_SOURCES
     sfizz/FloatEnvelopes.cpp
     sfizz/Logger.cpp
     sfizz/SfzFilter.cpp
+    sfizz/Effects.cpp
+    sfizz/effects/Nothing.cpp
+    sfizz/effects/Lofi.cpp
 )
 include (SfizzSIMDSourceFiles)
 

src/sfizz/AudioSpan.h

@@ -209,6 +209,22 @@ public:
         return {};
     }
 
+    /**
+     * @brief Convert implicitly to a pointer of channels
+     */
+    operator const float* const *() const noexcept
+    {
+        return spans.data();
+    }
+
+    /**
+     * @brief Convert implicitly to a pointer of channels
+     */
+    operator float* const *() noexcept
+    {
+        return spans.data();
+    }
+
     /**
      * @brief Get a Span<Type> corresponding to a specific channel
      *

src/sfizz/Config.h

@@ -69,6 +69,10 @@ namespace config {
      */
     const absl::string_view midnamManufacturer { "The Sfizz authors" };
     const absl::string_view midnamModel { "Sfizz" };
+    /**
+       Limit of how many "fxN" buses are accepted (in SFZv2, maximum is 4)
+     */
+    constexpr int maxEffectBuses { 256 };
 } // namespace config
 
 // Enable or disable SIMD accelerators by default

src/sfizz/Effects.cpp

@@ -0,0 +1,137 @@
+// SPDX-License-Identifier: BSD-2-Clause
+
+// This code is part of the sfizz library and is licensed under a BSD 2-clause
+// license. You should have receive a LICENSE.md file along with the code.
+// If not, contact the sfizz maintainers at https://github.com/sfztools/sfizz
+
+#include "Effects.h"
+#include "AudioSpan.h"
+#include "Opcode.h"
+#include "SIMDHelpers.h"
+#include "Config.h"
+#include "effects/Nothing.h"
+#include "effects/Lofi.h"
+#include <algorithm>
+
+namespace sfz {
+
+void EffectFactory::registerStandardEffectTypes()
+{
+    // TODO
+    registerEffectType("lofi", fx::Lofi::makeInstance);
+}
+
+void EffectFactory::registerEffectType(absl::string_view name, Effect::MakeInstance& make)
+{
+    FactoryEntry ent;
+    ent.name = std::string(name);
+    ent.make = &make;
+    _entries.push_back(std::move(ent));
+}
+
+Effect* EffectFactory::makeEffect(absl::Span<const Opcode> members)
+{
+    const Opcode* opcode = nullptr;
+
+    for (auto it = members.rbegin(); it != members.rend() && !opcode; ++it) {
+        if (it->lettersOnlyHash == hash("type"))
+            opcode = &*it;
+    }
+
+    if (!opcode) {
+        DBG("The effect does not specify a type");
+        return new sfz::fx::Nothing;
+    }
+
+    absl::string_view type = opcode->value;
+
+    auto it = _entries.begin();
+    auto end = _entries.end();
+    for (; it != end && it->name != type; ++it)
+        ;
+
+    if (it == end) {
+        DBG("Unsupported effect type: " << type);
+        return new sfz::fx::Nothing;
+    }
+
+    Effect* fx = it->make(members);
+    if (!fx) {
+        DBG("Could not instantiate effect of type: " << type);
+        return new sfz::fx::Nothing;
+    }
+
+    return fx;
+}
+
+///
+EffectBus::EffectBus()
+{
+}
+
+EffectBus::~EffectBus()
+{
+}
+
+void EffectBus::addEffect(std::unique_ptr<Effect> fx)
+{
+    _effects.emplace_back(std::move(fx));
+}
+
+void EffectBus::clearInputs(unsigned nframes)
+{
+    AudioSpan<float>(_inputs).first(nframes).fill(0.0f);
+    AudioSpan<float>(_outputs).first(nframes).fill(0.0f);
+}
+
+void EffectBus::addToInputs(const float* const addInput[], float addGain, unsigned nframes)
+{
+    if (addGain == 0)
+        return;
+
+    for (unsigned c = 0; c < EffectChannels; ++c) {
+        absl::Span<const float> addIn(addInput[c], nframes);
+        sfz::multiplyAdd(addGain, addIn, _inputs.getSpan(c));
+    }
+}
+
+void EffectBus::init(double sampleRate)
+{
+    for (const auto& effectPtr : _effects)
+        effectPtr->init(sampleRate);
+}
+
+void EffectBus::clear()
+{
+    for (const auto& effectPtr : _effects)
+        effectPtr->clear();
+}
+
+void EffectBus::process(unsigned nframes)
+{
+    size_t numEffects = _effects.size();
+
+    if (numEffects > 0 && hasNonZeroOutput()) {
+        _effects[0]->process(
+            AudioSpan<float>(_inputs), AudioSpan<float>(_outputs), nframes);
+        for (size_t i = 1; i < numEffects; ++i)
+            _effects[i]->process(
+                AudioSpan<float>(_outputs), AudioSpan<float>(_outputs), nframes);
+    } else
+        fx::Nothing().process(
+            AudioSpan<float>(_inputs), AudioSpan<float>(_outputs), nframes);
+}
+
+void EffectBus::mixOutputsTo(float* const mainOutput[], float* const mixOutput[], unsigned nframes)
+{
+    const float gainToMain = _gainToMain;
+    const float gainToMix = _gainToMix;
+
+    for (unsigned c = 0; c < EffectChannels; ++c) {
+        absl::Span<const float> fxOut = _outputs.getConstSpan(c);
+        sfz::multiplyAdd(gainToMain, fxOut, absl::Span<float>(mainOutput[c], nframes));
+        sfz::multiplyAdd(gainToMix, fxOut, absl::Span<float>(mixOutput[c], nframes));
+    }
+}
+
+} // namespace sfz

src/sfizz/Effects.h

@@ -0,0 +1,147 @@
+// SPDX-License-Identifier: BSD-2-Clause
+
+// This code is part of the sfizz library and is licensed under a BSD 2-clause
+// license. You should have receive a LICENSE.md file along with the code.
+// If not, contact the sfizz maintainers at https://github.com/sfztools/sfizz
+
+#pragma once
+#include "AudioBuffer.h"
+#include "absl/strings/string_view.h"
+#include "absl/types/span.h"
+#include <array>
+#include <vector>
+#include <memory>
+
+namespace sfz {
+struct Opcode;
+
+enum {
+    // Number of channels processed by effects
+    EffectChannels = 2,
+};
+
+/**
+   @brief Abstract base of SFZ effects
+ */
+class Effect {
+public:
+    virtual ~Effect() {}
+
+    /**
+       @brief Initializes with the given sample rate.
+     */
+    virtual void init(double sampleRate) = 0;
+
+    /**
+       @brief Reset the state to initial.
+     */
+    virtual void clear() = 0;
+
+    /**
+       @brief Computes a cycle of the effect in stereo.
+     */
+    virtual void process(const float* const inputs[], float* const outputs[], unsigned nframes) = 0;
+
+    /**
+       @brief Type of the factory function used to instantiate an effect given
+              the contents of the <effect> block
+     */
+    typedef Effect* (MakeInstance)(absl::Span<const Opcode> members);
+};
+
+/**
+   @brief SFZ effects factory
+ */
+class EffectFactory {
+public:
+    /**
+       @brief Registers all available standard effects into the factory.
+     */
+    void registerStandardEffectTypes();
+
+    /**
+       @brief Registers a user-defined effect into the factory.
+     */
+    void registerEffectType(absl::string_view name, Effect::MakeInstance& make);
+
+    /**
+       @brief Instantiates an effect given the contents of the <effect> block.
+     */
+    Effect* makeEffect(absl::Span<const Opcode> members);
+
+private:
+    struct FactoryEntry {
+        std::string name;
+        Effect::MakeInstance* make;
+    };
+
+    std::vector<FactoryEntry> _entries;
+};
+
+/**
+   @brief Sequence of effects processed in series
+ */
+class EffectBus {
+public:
+    EffectBus();
+    ~EffectBus();
+
+    /**
+       @brief Adds an effect at the end of the bus.
+     */
+    void addEffect(std::unique_ptr<Effect> fx);
+
+    /**
+       @brief Checks whether this bus can produce output.
+     */
+    bool hasNonZeroOutput() const { return _gainToMain != 0 || _gainToMix != 0; }
+
+    /**
+       @brief Sets the amount of effect output going to the main.
+     */
+    void setGainToMain(float gain) { _gainToMain = gain; }
+
+    /**
+       @brief Sets the amount of effect output going to the mix.
+     */
+    void setGainToMix(float gain) { _gainToMix = gain; }
+
+    /**
+       @brief Resets the input buffers to zero.
+     */
+    void clearInputs(unsigned nframes);
+
+    /**
+       @brief Adds some audio into the input buffer.
+     */
+    void addToInputs(const float* const addInput[], float addGain, unsigned nframes);
+
+    /**
+       @brief Initializes all effects in the bus with the given sample rate.
+     */
+    void init(double sampleRate);
+
+    /**
+       @brief Resets the state of all effects in the bus.
+     */
+    void clear();
+
+    /**
+       @brief Computes a cycle of the effect bus.
+     */
+    void process(unsigned nframes);
+
+    /**
+       @brief Mixes the outputs into a pair of stereo signals: Main and Mix.
+     */
+    void mixOutputsTo(float* const mainOutput[], float* const mixOutput[], unsigned nframes);
+
+private:
+    std::vector<std::unique_ptr<Effect>> _effects;
+    AudioBuffer<float> _inputs { EffectChannels, config::defaultSamplesPerBlock };
+    AudioBuffer<float> _outputs { EffectChannels, config::defaultSamplesPerBlock };
+    float _gainToMain = 0.0;
+    float _gainToMix = 0.0;
+};
+
+} // namespace sfz

src/sfizz/Region.cpp

@@ -733,6 +733,20 @@ bool sfz::Region::parseOpcode(const Opcode& opcode)
         setCCPairFromOpcode(opcode, amplitudeEG.ccSustain, Default::egOnCCPercentRange);
         break;
 
+    case hash("effect"): // effect&
+        {
+            const auto effectNumber = opcode.backParameter();
+            if (!effectNumber || *effectNumber < 1 || *effectNumber > config::maxEffectBuses)
+                break;
+            auto value = readOpcode<float>(opcode.value, {0, 100});
+            if (!value)
+                break;
+            if (static_cast<size_t>(*effectNumber + 1) > gainToEffect.size())
+                gainToEffect.resize(*effectNumber + 1);
+            gainToEffect[*effectNumber] = *value / 100;
+            break;
+        }
+
     // Ignored opcodes
     case hash("hichan"):
     case hash("lochan"):
@@ -1073,3 +1087,11 @@ void sfz::Region::offsetAllKeys(int offset) noexcept
         crossfadeKeyOutRange.setEnd(offsetAndClamp(end, offset, Default::keyRange));
     }
 }
+
+float sfz::Region::getGainToEffectBus(unsigned number) const noexcept
+{
+    if (number >= gainToEffect.size())
+        return 0.0;
+
+    return gainToEffect[number];
+}

src/sfizz/Region.h

@@ -39,6 +39,9 @@ struct Region {
     : midiState(midiState), defaultPath(std::move(defaultPath))
     {
         ccSwitched.set();
+
+        gainToEffect.reserve(5); // sufficient room for main and fx1-4
+        gainToEffect.push_back(1.0); // contribute 100% into the main bus
     }
     Region(const Region&) = default;
     ~Region() = default;
@@ -206,6 +209,12 @@ struct Region {
 
     bool hasKeyswitches() const noexcept { return keyswitchDown || keyswitchUp || keyswitch || previousNote; }
 
+    /**
+     * @brief Get the gain this region contributes into the input of the Nth
+     *        effect bus
+     */
+    float getGainToEffectBus(unsigned number) const noexcept;
+
     // Sound source: sample playback
     std::string sample {}; // Sample
     float delay { Default::delay }; // delay
@@ -297,6 +306,10 @@ struct Region {
     EGDescription filterEG;
 
     bool isStereo { false };
+
+    // Effects
+    std::vector<float> gainToEffect;
+
 private:
     const MidiState& midiState;
     bool keySwitched { true };

src/sfizz/Synth.cpp

@@ -21,12 +21,16 @@
 using namespace std::literals;
 
 sfz::Synth::Synth()
+    : Synth(config::numVoices)
 {
-    resetVoices(this->numVoices);
 }
 
 sfz::Synth::Synth(int numVoices)
 {
+    effectFactory.registerStandardEffectTypes();
+
+    effectBuses.reserve(5); // sufficient room for main and fx1-4
+
     resetVoices(numVoices);
 }
 
@@ -70,7 +74,7 @@ void sfz::Synth::callback(absl::string_view header, const std::vector<Opcode>& m
         numCurves++;
         break;
     case hash("effect"):
-        // TODO: implement effects
+        handleEffectOpcodes(members);
         break;
     default:
         std::cerr << "Unknown header: " << header << '\n';
@@ -118,6 +122,10 @@ void sfz::Synth::clear()
     for (auto& list: ccActivationLists)
         list.clear();
     regions.clear();
+    effectBuses.clear();
+    EffectBus* mainBus = new EffectBus;
+    effectBuses.emplace_back(mainBus);
+    mainBus->setGainToMain(1.0);
     resources.filePool.clear();
     resources.logger.clear();
     numGroups = 0;
@@ -185,6 +193,75 @@ void sfz::Synth::handleControlOpcodes(const std::vector<Opcode>& members)
     }
 }
 
+void sfz::Synth::handleEffectOpcodes(const std::vector<Opcode>& members)
+{
+    absl::string_view busName = "main";
+
+    auto getOrCreateBus = [this](unsigned index) -> EffectBus& {
+        if (index + 1 > effectBuses.size())
+            effectBuses.resize(index + 1);
+        EffectBusPtr &slot = effectBuses[index];
+        if (!slot)
+            slot.reset(new EffectBus);
+        return *slot;
+    };
+
+    for (const Opcode& opcode : members) {
+        switch (opcode.lettersOnlyHash) {
+        case hash("bus"):
+            busName = opcode.value;
+            break;
+
+        // note(jpc): gain opcodes are linear volumes in % units
+
+        case hash("directtomain"):
+            if (auto valueOpt = readOpcode<float>(opcode.value, {0, 100}))
+                getOrCreateBus(0).setGainToMain(*valueOpt / 100);
+            break;
+
+        case hash("fxtomain"): // fx&tomain
+            if (auto numberOpt = opcode.firstParameter()) {
+                unsigned number = *numberOpt;
+                if (number < 1 || number > config::maxEffectBuses)
+                    break;
+                if (auto valueOpt = readOpcode<float>(opcode.value, {0, 100}))
+                    getOrCreateBus(number).setGainToMain(*valueOpt / 100);
+            }
+            break;
+
+        case hash("fxtomix"): // fx&tomix
+            if (auto numberOpt = opcode.firstParameter()) {
+                unsigned number = *numberOpt;
+                if (number < 1 || number > config::maxEffectBuses)
+                    break;
+                if (auto valueOpt = readOpcode<float>(opcode.value, {0, 100}))
+                    getOrCreateBus(number).setGainToMix(*valueOpt / 100);
+            }
+            break;
+        }
+    }
+
+    unsigned busIndex;
+    if (busName.empty() || busName == "main")
+        busIndex = 0;
+    else if (busName.size() > 2 && busName.substr(0, 2) == "fx" &&
+             absl::SimpleAtoi(busName.substr(2), &busIndex) &&
+             busIndex >= 1 && busIndex <= config::maxEffectBuses) {
+        // an effect bus fxN, with N usually in [1,4]
+    }
+    else {
+        DBG("Unsupported effect bus: " << busName);
+        return;
+    }
+
+    // create the effect and add it
+    EffectBus& bus = getOrCreateBus(busIndex);
+    Effect* fx = effectFactory.makeEffect(members);
+    bus.addEffect(std::unique_ptr<Effect>(fx));
+
+    fx->init(sampleRate);
+}
+
 void addEndpointsToVelocityCurve(sfz::Region& region)
 {
     if (region.velocityPoints.size() > 0) {
@@ -385,6 +462,7 @@ void sfz::Synth::setSamplesPerBlock(int samplesPerBlock) noexcept
 
     this->samplesPerBlock = samplesPerBlock;
     this->tempBuffer.resize(samplesPerBlock);
+    this->tempMixNodeBuffer.resize(samplesPerBlock);
     for (auto& voice : voices)
         voice->setSamplesPerBlock(samplesPerBlock);
 }
@@ -402,13 +480,17 @@ void sfz::Synth::setSampleRate(float sampleRate) noexcept
 
     resources.filterPool.setSampleRate(sampleRate);
     resources.eqPool.setSampleRate(sampleRate);
+
+    for (size_t i = 0, n = effectBuses.size(); i < n; ++i) {
+        if (EffectBus* bus = effectBuses[i].get())
+            bus->init(sampleRate);
+    }
 }
 
 void sfz::Synth::renderBlock(AudioSpan<float> buffer) noexcept
 {
     ScopedFTZ ftz;
 
-
     if (freeWheeling)
         resources.filePool.waitForBackgroundLoading();
 
@@ -416,32 +498,71 @@ void sfz::Synth::renderBlock(AudioSpan<float> buffer) noexcept
     if (!canEnterCallback)
         return;
 
+    size_t numFrames = buffer.getNumFrames();
+    size_t numEffectBuses = effectBuses.size();
+    auto temp = AudioSpan<float>(tempBuffer).first(numFrames);
+    auto tempMixNode = AudioSpan<float>(tempMixNodeBuffer).first(numFrames);
+
+    // Prepare the effect inputs. They are mixes of per-region outputs.
+    for (size_t i = 0; i < numEffectBuses; ++i) {
+        if (EffectBus* bus = effectBuses[i].get())
+            bus->clearInputs(numFrames);
+    }
+
+    //
     CallbackBreakdown callbackBreakdown;
     int numActiveVoices { 0 };
     { // Main render block
         ScopedTiming logger { callbackBreakdown.renderMethod };
         buffer.fill(0.0f);
+        tempMixNode.fill(0.0f);
         resources.filePool.cleanupPromises();
 
-
-        auto tempSpan = AudioSpan<float>(tempBuffer).first(buffer.getNumFrames());
         for (auto& voice : voices) {
-            if (!voice->isFree()) {
+            if (voice->isFree())
-                numActiveVoices++;
+                continue;
-                voice->renderBlock(tempSpan);
-                buffer.add(tempSpan);
-                callbackBreakdown.data += voice->getLastDataDuration();
-                callbackBreakdown.amplitude += voice->getLastAmplitudeDuration();
-                callbackBreakdown.filters += voice->getLastFilterDuration();
-                callbackBreakdown.panning += voice->getLastPanningDuration();
-            }
-        }
 
-        buffer.applyGain(db2mag(volume));
+            const Region* region = voice->getRegion();
+
+            numActiveVoices++;
+            voice->renderBlock(temp);
+
+            // Add the output into the effects linked to this region
+            for (size_t i = 0; i < numEffectBuses; ++i) {
+                if (EffectBus* bus = effectBuses[i].get()) {
+                    float addGain = region->getGainToEffectBus(i);
+                    bus->addToInputs(temp, addGain, numFrames);
+                }
+            }
+
+            callbackBreakdown.data += voice->getLastDataDuration();
+            callbackBreakdown.amplitude += voice->getLastAmplitudeDuration();
+            callbackBreakdown.filters += voice->getLastFilterDuration();
+            callbackBreakdown.panning += voice->getLastPanningDuration();
+        }
     }
 
+    // Apply effect buses
+    // -- note(jpc) there is always a "main" bus which is initially empty.
+    //    without any <effect>, the signal is just going to flow through it.
+    for (size_t i = 0; i < numEffectBuses; ++i) {
+        if (EffectBus* bus = effectBuses[i].get()) {
+            bus->process(numFrames);
+            bus->mixOutputsTo(buffer, tempMixNode, numFrames);
+        }
+    }
+
+    // Add the Mix output (fxNtomix opcodes)
+    // -- note(jpc) the purpose of the Mix output is not known.
+    //    perhaps it's designed as extension point for custom processing?
+    //    as default behavior, it adds itself to the Main signal.
+    buffer.add(tempMixNode);
+
+    // Apply the master volume
+    buffer.applyGain(db2mag(volume));
+
     callbackBreakdown.dispatch = dispatchDuration;
-    resources.logger.logCallbackTime(std::move(callbackBreakdown), numActiveVoices, buffer.getNumFrames());
+    resources.logger.logCallbackTime(std::move(callbackBreakdown), numActiveVoices, numFrames);
 
     // Reset the dispatch counter
     dispatchDuration = Duration(0);

src/sfizz/Synth.h

@@ -9,6 +9,7 @@
 #include "Parser.h"
 #include "Voice.h"
 #include "Region.h"
+#include "Effects.h"
 #include "LeakDetector.h"
 #include "MidiState.h"
 #include "AudioSpan.h"
@@ -400,6 +401,12 @@ private:
      * @param members the opcodes of the <control> block
      */
     void handleControlOpcodes(const std::vector<Opcode>& members);
+    /**
+     * @brief Helper function to dispatch <effect> opcodes
+     *
+     * @param members the opcodes of the <effect> block
+     */
+    void handleEffectOpcodes(const std::vector<Opcode>& members);
     /**
      * @brief Helper function to merge all the currently active opcodes
      * as set by the successive callbacks and create a new region to store
@@ -441,8 +448,14 @@ private:
     std::array<RegionPtrVector, 128> noteActivationLists;
     std::array<RegionPtrVector, config::numCCs> ccActivationLists;
 
-    // Internal temporary buffer
+    // Effect factory and buses
+    EffectFactory effectFactory;
+    typedef std::unique_ptr<EffectBus> EffectBusPtr;
+    std::vector<EffectBusPtr> effectBuses; // 0 is "main", 1-N are "fx1"-"fxN"
+
+    // Intermediate buffers
     AudioBuffer<float> tempBuffer { 2, config::defaultSamplesPerBlock };
+    AudioBuffer<float> tempMixNodeBuffer { 2, config::defaultSamplesPerBlock };
 
     int samplesPerBlock { config::defaultSamplesPerBlock };
     float sampleRate { config::defaultSampleRate };

src/sfizz/effects/Lofi.cpp

@@ -0,0 +1,213 @@
+// SPDX-License-Identifier: BSD-2-Clause
+
+// This code is part of the sfizz library and is licensed under a BSD 2-clause
+// license. You should have receive a LICENSE.md file along with the code.
+// If not, contact the sfizz maintainers at https://github.com/sfztools/sfizz
+
+/**
+   Note(jpc): implementation status
+
+- [x] bitred
+- [ ] bitred_oncc
+- [ ] bitred_smoothcc
+- [ ] bitred_stepcc
+- [ ] bitred_curvecc
+
+- [x] decim
+- [ ] decim_oncc
+- [ ] decim_smoothcc
+- [ ] decim_stepcc
+- [ ] decim_curvecc
+
+- [ ] egN_bitred
+- [ ] egN_bitred_oncc
+- [ ] lfoN_bitred
+- [ ] lfoN_bitred_oncc
+- [ ] lfoN_bitred_smoothcc
+- [ ] lfoN_bitred_stepcc
+
+- [ ] egN_decim
+- [ ] egN_decim_oncc
+- [ ] lfoN_decim
+- [ ] lfoN_decim_oncc
+- [ ] lfoN_decim_smoothcc
+- [ ] lfoN_decim_stepcc
+
+ */
+
+#include "Lofi.h"
+#include "Opcode.h"
+#include <memory>
+#include <algorithm>
+#include <cstring>
+#include <cmath>
+
+namespace sfz {
+namespace fx {
+
+    void Lofi::init(double sampleRate)
+    {
+        for (unsigned c = 0; c < EffectChannels; ++c) {
+            _bitred[c].init(sampleRate);
+            _decim[c].init(sampleRate);
+        }
+    }
+
+    void Lofi::clear()
+    {
+        for (unsigned c = 0; c < EffectChannels; ++c) {
+            _bitred[c].clear();
+            _decim[c].clear();
+        }
+    }
+
+    void Lofi::process(const float* const inputs[2], float* const outputs[2], unsigned nframes)
+    {
+        for (unsigned c = 0; c < EffectChannels; ++c) {
+            _bitred[c].setDepth(_bitred_depth);
+            _bitred[c].process(inputs[c], outputs[c], nframes);
+
+            _decim[c].setDepth(_decim_depth);
+            _decim[c].process(outputs[c], outputs[c], nframes);
+        }
+    }
+
+    Effect* Lofi::makeInstance(absl::Span<const Opcode> members)
+    {
+        std::unique_ptr<Lofi> fx { new Lofi };
+
+        for (const Opcode& opcode : members) {
+            switch (opcode.lettersOnlyHash) {
+            case hash("bitred"):
+                setValueFromOpcode(opcode, fx->_bitred_depth, { 0.0, 100.0 });
+                break;
+            case hash("decim"):
+                setValueFromOpcode(opcode, fx->_decim_depth, { 0.0, 100.0 });
+                break;
+            }
+        }
+
+        return fx.release();
+    }
+
+    ///
+    void Lofi::Bitred::init(double sampleRate)
+    {
+        (void)sampleRate;
+
+        static constexpr double coefs2x[12] = { 0.036681502163648017, 0.13654762463195794, 0.27463175937945444, 0.42313861743656711, 0.56109869787919531, 0.67754004997416184, 0.76974183386322703, 0.83988962484963892, 0.89226081800387902, 0.9315419599631839, 0.96209454837808417, 0.98781637073289585 };
+        fDownsampler2x.set_coefs(coefs2x);
+    }
+
+    void Lofi::Bitred::clear()
+    {
+        fLastValue = 0.0;
+        fDownsampler2x.clear_buffers();
+    }
+
+    void Lofi::Bitred::setDepth(float depth)
+    {
+        fDepth = std::max(0.0f, std::min(100.0f, depth));
+    }
+
+    void Lofi::Bitred::process(const float* in, float* out, uint32_t nframes)
+    {
+        float depth = fDepth;
+
+        if (depth == 0) {
+            if (in != out)
+                std::memcpy(out, in, nframes * sizeof(float));
+            clear();
+            return;
+        }
+
+        float lastValue = fLastValue;
+        hiir::Downsampler2xFpu<12>& downsampler2x = fDownsampler2x;
+
+        float steps = (1.0f + (100.0f - depth)) * 0.75f;
+
+        for (uint32_t i = 0; i < nframes; ++i) {
+            float x = in[i];
+
+            float y = std::copysign((int)(0.5f + std::fabs(x * steps)), x) * (1 / steps);
+
+            float y2x[2];
+            y2x[0] = (y != lastValue) ? (0.5f * (y + lastValue)) : y;
+            y2x[1] = y;
+
+            lastValue = y;
+
+            y = downsampler2x.process_sample(y2x);
+            out[i] = y;
+        }
+
+        fLastValue = lastValue;
+    }
+
+    ///
+    void Lofi::Decim::init(double sampleRate)
+    {
+        fSampleTime = 1.0 / sampleRate;
+
+        static constexpr double coefs2x[12] = { 0.036681502163648017, 0.13654762463195794, 0.27463175937945444, 0.42313861743656711, 0.56109869787919531, 0.67754004997416184, 0.76974183386322703, 0.83988962484963892, 0.89226081800387902, 0.9315419599631839, 0.96209454837808417, 0.98781637073289585 };
+        fDownsampler2x.set_coefs(coefs2x);
+    }
+
+    void Lofi::Decim::clear()
+    {
+        fPhase = 0.0;
+        fLastValue = 0.0;
+        fDownsampler2x.clear_buffers();
+    }
+
+    void Lofi::Decim::setDepth(float depth)
+    {
+        fDepth = std::max(0.0f, std::min(100.0f, depth));
+    }
+
+    void Lofi::Decim::process(const float* in, float* out, uint32_t nframes)
+    {
+        float depth = fDepth;
+
+        if (depth == 0) {
+            if (in != out)
+                std::memcpy(out, in, nframes * sizeof(float));
+            clear();
+            return;
+        }
+
+        float dt;
+        {
+            // exponential curve fit
+            float a = 1.289079e+00, b = 1.384141e-01, c = 1.313298e-04;
+            dt = std::pow(a, b * depth) * c - c;
+            dt = fSampleTime / dt;
+        }
+
+        float phase = fPhase;
+        float lastValue = fLastValue;
+        hiir::Downsampler2xFpu<12>& downsampler2x = fDownsampler2x;
+
+        for (uint32_t i = 0; i < nframes; ++i) {
+            float x = in[i];
+
+            phase += dt;
+            float y = (phase > 1.0f) ? x : lastValue;
+            phase -= (int)phase;
+
+            float y2x[2];
+            y2x[0] = (y != lastValue) ? (0.5f * (y + lastValue)) : y;
+            y2x[1] = y;
+
+            lastValue = y;
+
+            y = downsampler2x.process_sample(y2x);
+            out[i] = y;
+        }
+
+        fPhase = phase;
+        fLastValue = lastValue;
+    }
+
+} // namespace fx
+} // namespace sfz

src/sfizz/effects/Lofi.h

@@ -0,0 +1,79 @@
+// SPDX-License-Identifier: BSD-2-Clause
+
+// This code is part of the sfizz library and is licensed under a BSD 2-clause
+// license. You should have receive a LICENSE.md file along with the code.
+// If not, contact the sfizz maintainers at https://github.com/sfztools/sfizz
+
+#pragma once
+#include "Effects.h"
+#include "hiir/Downsampler2xFpu.h"
+
+namespace sfz {
+namespace fx {
+
+    /**
+     * @brief Bit crushing effect
+     */
+    class Lofi : public Effect {
+    public:
+        /**
+         * @brief Initializes with the given sample rate.
+         */
+        void init(double sampleRate) override;
+
+        /**
+         * @brief Reset the state to initial.
+         */
+        void clear() override;
+
+        /**
+          * @brief Computes a cycle of the effect in stereo.
+          */
+        void process(const float* const inputs[], float* const outputs[], unsigned nframes) override;
+
+        /**
+          * @brief Instantiates given the contents of the <effect> block.
+          */
+        static Effect* makeInstance(absl::Span<const Opcode> members);
+
+    private:
+        float _bitred_depth = 0;
+        float _decim_depth = 0;
+
+        ///
+        class Bitred {
+        public:
+            void init(double sampleRate);
+            void clear();
+            void setDepth(float depth);
+            void process(const float* in, float* out, uint32_t nframes);
+
+        private:
+            float fDepth = 0.0;
+            float fLastValue = 0.0;
+            hiir::Downsampler2xFpu<12> fDownsampler2x;
+        };
+
+        ///
+        class Decim {
+        public:
+            void init(double sampleRate);
+            void clear();
+            void setDepth(float depth);
+            void process(const float* in, float* out, uint32_t nframes);
+
+        private:
+            float fSampleTime = 0.0;
+            float fDepth = 0.0;
+            float fPhase = 0.0;
+            float fLastValue = 0.0;
+            hiir::Downsampler2xFpu<12> fDownsampler2x;
+        };
+
+        ///
+        Bitred _bitred[EffectChannels];
+        Decim _decim[EffectChannels];
+    };
+
+} // namespace fx
+} // namespace sfz

src/sfizz/effects/Nothing.cpp

@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: BSD-2-Clause
+
+// This code is part of the sfizz library and is licensed under a BSD 2-clause
+// license. You should have receive a LICENSE.md file along with the code.
+// If not, contact the sfizz maintainers at https://github.com/sfztools/sfizz
+
+#include "Nothing.h"
+#include <cstring>
+
+namespace sfz {
+namespace fx {
+
+    void Nothing::init(double sampleRate)
+    {
+        (void)sampleRate;
+    }
+
+    void Nothing::clear()
+    {
+    }
+
+    void Nothing::process(const float* const inputs[], float* const outputs[], unsigned nframes)
+    {
+        for (unsigned c = 0; c < EffectChannels; ++c) {
+            if (inputs[c] != outputs[c])
+                std::memcpy(outputs[c], inputs[c], nframes * sizeof(float));
+        }
+    }
+
+} // namespace fx
+} // namespace sfz

src/sfizz/effects/Nothing.h

@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: BSD-2-Clause
+
+// This code is part of the sfizz library and is licensed under a BSD 2-clause
+// license. You should have receive a LICENSE.md file along with the code.
+// If not, contact the sfizz maintainers at https://github.com/sfztools/sfizz
+
+#pragma once
+#include "Effects.h"
+
+namespace sfz {
+namespace fx {
+
+    /**
+     * @brief Effect which does nothing
+     */
+    class Nothing : public Effect {
+    public:
+        /**
+         * @brief Initializes with the given sample rate.
+         */
+        void init(double sampleRate) override;
+
+        /**
+         * @brief Reset the state to initial.
+         */
+        void clear() override;
+
+        /**
+         * @brief Copy the input signal to the output
+         */
+        void process(const float* const inputs[], float* const outputs[], unsigned nframes) override;
+    };
+
+} // namespace fx
+} // namespace sfz