diff --git a/src/sfizz/ModifierHelpers.h b/src/sfizz/ModifierHelpers.h
index f853b136..5ea57c02 100644
--- a/src/sfizz/ModifierHelpers.h
+++ b/src/sfizz/ModifierHelpers.h
@@ -1,3 +1,9 @@
+// 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 "Range.h"
@@ -55,6 +61,14 @@ float crossfadeOut(const sfz::Range<T>& crossfadeRange, U value, SfzCrossfadeCur
     return 1.0f;
 }
 
+/**
+ * @brief Compute a linear envelope based on events, with a lambda applied to the event values
+ *
+ * @tparam F
+ * @param events
+ * @param envelope
+ * @param lambda
+ */
 template <class F>
 void linearEnvelope(const EventVector& events, absl::Span<float> envelope, F&& lambda)
 {
@@ -76,6 +90,15 @@ void linearEnvelope(const EventVector& events, absl::Span<float> envelope, F&& l
     fill(envelope.subspan(lastDelay), lastValue);
 }
 
+/**
+ * @brief Compute a quantized linear envelope based on events, with a lambda applied to the event values
+ *
+ * @tparam F
+ * @param events
+ * @param envelope
+ * @param lambda
+ * @param step
+ */
 template <class F>
 void linearEnvelope(const EventVector& events, absl::Span<float> envelope, F&& lambda, float step)
 {
@@ -116,6 +139,15 @@ void linearEnvelope(const EventVector& events, absl::Span<float> envelope, F&& l
     fill(envelope.subspan(lastDelay), lastValue);
 }
 
+
+/**
+ * @brief Compute a multiplicative envelope based on events, with a lambda applied to the event values
+ *
+ * @tparam F
+ * @param events
+ * @param envelope
+ * @param lambda
+ */
 template <class F>
 void multiplicativeEnvelope(const EventVector& events, absl::Span<float> envelope, F&& lambda)
 {
@@ -139,6 +171,16 @@ void multiplicativeEnvelope(const EventVector& events, absl::Span<float> envelop
     fill(envelope.subspan(lastDelay), lastValue);
 }
 
+/**
+ * @brief Compute a quantized multiplicative envelope based on events, with a lambda applied to the event values
+ *
+ * @tparam F
+ * @tparam Round is true if the quantization rounds rather than truncs the elements
+ * @param events
+ * @param envelope
+ * @param lambda
+ * @param step
+ */
 template <class F, bool Round = false>
 void multiplicativeEnvelope(const EventVector& events, absl::Span<float> envelope, F&& lambda, float step)
 {
@@ -186,18 +228,46 @@ void multiplicativeEnvelope(const EventVector& events, absl::Span<float> envelop
     fill(envelope.subspan(lastDelay), lastValue);
 }
 
+/**
+ * @brief Alias for a multiplicative envelope that rounds the elements
+ *
+ * @tparam F
+ * @param events
+ * @param envelope
+ * @param lambda
+ * @param step
+ */
 template <class F>
 void pitchBendEnvelope(const EventVector& events, absl::Span<float> envelope, F&& lambda, float step)
 {
     multiplicativeEnvelope<F, true>(events, envelope, std::forward<F>(lambda), step);
 }
 
+/**
+ * @brief Alias for a multiplicative envelope
+ *
+ * @tparam F
+ * @param events
+ * @param envelope
+ * @param lambda
+ */
 template <class F>
 void pitchBendEnvelope(const EventVector& events, absl::Span<float> envelope, F&& lambda)
 {
     multiplicativeEnvelope<F>(events, envelope, std::forward<F>(lambda));
 }
 
+/**
+ * @brief Builds a linear envelope, possibly quantized, based on the events fetched
+ * from a midi state and the modifier data. This is a helper function for recurrent
+ * code in the voice logic.
+ *
+ * @tparam F
+ * @param resources
+ * @param span
+ * @param ccData
+ * @param lambda
+ */
 template <class F>
 void linearModifier(const sfz::Resources& resources, absl::Span<float> span, const sfz::CCData<sfz::Modifier>& ccData, F&& lambda)
 {
@@ -217,6 +287,17 @@ void linearModifier(const sfz::Resources& resources, absl::Span<float> span, con
     }
 }
 
+/**
+ * @brief Builds a multiplicative envelope, possibly quantized, based on the events fetched
+ * from a midi state and the modifier data. This is a helper function for recurrent
+ * code in the voice logic.
+ *
+ * @tparam F
+ * @param resources
+ * @param span
+ * @param ccData
+ * @param lambda
+ */
 template <class F>
 void multiplicativeModifier(const sfz::Resources& resources, absl::Span<float> span, const sfz::CCData<sfz::Modifier>& ccData, F&& lambda)
 {
@@ -236,6 +317,15 @@ void multiplicativeModifier(const sfz::Resources& resources, absl::Span<float> s
     }
 }
 
+/**
+ * @brief Alias for a simple linear modifier with no lambda
+ *
+ * @tparam F
+ * @param resources
+ * @param span
+ * @param ccData
+ * @param lambda
+ */
 inline void linearModifier(const sfz::Resources& resources, absl::Span<float> span, const sfz::CCData<sfz::Modifier>& ccData)
 {
     linearModifier(resources, span, ccData, [](float x) { return x; });
diff --git a/src/sfizz/Modifiers.h b/src/sfizz/Modifiers.h
index bdf4508a..3a6573be 100644
--- a/src/sfizz/Modifiers.h
+++ b/src/sfizz/Modifiers.h
@@ -1,3 +1,9 @@
+// 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 <numeric>
 #include <array>
@@ -5,6 +11,10 @@
 
 namespace sfz {
 
+/**
+ * @brief Base modifier class
+ *
+ */
 struct Modifier {
     float value { 0.0f };
     float step { 0.0f };
@@ -23,6 +33,11 @@ enum class Mod : size_t {
     sentinel
 };
 
+/**
+ * @brief Vectors of elements indexed on modifiers with casting and iterators
+ *
+ * @tparam T
+ */
 template <class T>
 class ModifierVector : public std::vector<T> {
 public:
@@ -30,6 +45,11 @@ public:
     const T& operator[](sfz::Mod idx) const { return this->std::vector<T>::operator[](static_cast<size_t>(idx)); }
 };
 
+/**
+ * @brief Array of elements indexed on modifiers with casting and iterators
+ *
+ * @tparam T
+ */
 template <class T>
 class ModifierArray {
 public:
diff --git a/src/sfizz/Smoothers.cpp b/src/sfizz/Smoothers.cpp
index 9f40b67d..252d1f50 100644
--- a/src/sfizz/Smoothers.cpp
+++ b/src/sfizz/Smoothers.cpp
@@ -1,3 +1,9 @@
+// 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 "Smoothers.h"
 
 namespace sfz {
diff --git a/src/sfizz/Smoothers.h b/src/sfizz/Smoothers.h
index 4793f423..20eb4e3a 100644
--- a/src/sfizz/Smoothers.h
+++ b/src/sfizz/Smoothers.h
@@ -1,3 +1,9 @@
+// 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 "Config.h"
@@ -9,11 +15,34 @@
 #include <array>
 
 namespace sfz {
+/**
+ * @brief Wrapper class for a one pole filter smoother
+ *
+ */
 class Smoother {
 public:
     Smoother();
+    /**
+     * @brief Set the filter cutoff based on the sfz smoothing value
+     * and the sample rate.
+     *
+     * @param smoothValue
+     * @param sampleRate
+     */
     void setSmoothing(uint8_t smoothValue, float sampleRate);
+    /**
+     * @brief Reset the filter state to a given value
+     *
+     * @param value
+     */
     void reset(float value = 0.0f);
+    /**
+     * @brief Process a span of data. Input and output can refer to the same
+     * memory.
+     *
+     * @param input
+     * @param output
+     */
     void process(absl::Span<const float> input, absl::Span<float> output);
 
 private:
diff --git a/src/sfizz/Voice.h b/src/sfizz/Voice.h
index adbe7d81..6967e780 100644
--- a/src/sfizz/Voice.h
+++ b/src/sfizz/Voice.h
@@ -333,13 +333,46 @@ private:
         const AudioSpan<const float>& source, AudioSpan<float>& dest,
         absl::Span<const int> indices, absl::Span<const float> coeffs);
 
+    /**
+     * @brief Compute the amplitude envelope, applied as a gain to a mono
+     * or stereo buffer
+     *
+     * @param modulationSpan
+     */
     void amplitudeEnvelope(absl::Span<float> modulationSpan) noexcept;
+    /**
+     * @brief Amplitude stage for a mono source
+     *
+     * @param buffer
+     */
     void ampStageMono(AudioSpan<float> buffer) noexcept;
+    /**
+     * @brief Amplitude stage for a stereo source
+     *
+     * @param buffer
+     */
     void ampStageStereo(AudioSpan<float> buffer) noexcept;
+    /**
+     * @brief Amplitude stage for a mono source
+     *
+     * @param buffer
+     */
     void panStageMono(AudioSpan<float> buffer) noexcept;
     void panStageStereo(AudioSpan<float> buffer) noexcept;
+    /**
+     * @brief Amplitude stage for a mono source
+     *
+     * @param buffer
+     */
     void filterStageMono(AudioSpan<float> buffer) noexcept;
     void filterStageStereo(AudioSpan<float> buffer) noexcept;
+    /**
+     * @brief Compute the pitch envelope. This envelope is meant to multiply
+     * the frequency parameter for each sample (which translates to floating
+     * point intervals for sample-based voices, or phases for generators)
+     *
+     * @param pitchSpan
+     */
     void pitchEnvelope(absl::Span<float> pitchSpan) noexcept;
 
     /**
@@ -348,6 +381,14 @@ private:
      */
     void removeVoiceFromRing() noexcept;
 
+    /**
+     * @brief Helper function to iterate jointly on modifiers and smoothers
+     * for a given modulation target of type sfz::Mod
+     *
+     * @tparam F
+     * @param modId
+     * @param lambda
+     */
     template <class F>
     void forEachWithSmoother(sfz::Mod modId, F&& lambda)
     {