Add AirWindowsVinylDither

CMakeLists.txt

@@ -56,6 +56,7 @@ if(NOT CMAKE_CROSSCOMPILING)
             "lib/grit/audio/dynamic/transient_shaper_test.cpp"
             "lib/grit/audio/envelope/envelope_follower_test.cpp"
             "lib/grit/audio/music/note_test.cpp"
+            "lib/grit/audio/noise/airwindows_vinyl_dither_test.cpp"
             "lib/grit/audio/noise/dither_test.cpp"
             "lib/grit/audio/noise/white_noise_test.cpp"
             "lib/grit/audio/waveshape/full_wave_rectifier_test.cpp"

lib/CMakeLists.txt

@@ -36,6 +36,7 @@ target_sources(grit-eurorack INTERFACE
         "grit/audio/music/note.hpp"
 
         "grit/audio/noise.hpp"
+        "grit/audio/noise/airwindows_vinyl_dither.hpp"
         "grit/audio/noise/dither.hpp"
         "grit/audio/noise/white_noise.hpp"
 

lib/grit/audio/noise.hpp

@@ -1,4 +1,5 @@
 #pragma once
 
+#include <grit/audio/noise/airwindows_vinyl_dither.hpp>
 #include <grit/audio/noise/dither.hpp>
-#include <grit/audio/noise/white_noise.hpp>
+#include <grit/audio/noise/white_noise.hpp>

lib/grit/audio/noise/airwindows_vinyl_dither.hpp

@@ -0,0 +1,124 @@
+#pragma once
+
+#include <etl/algorithm.hpp>
+#include <etl/array.hpp>
+#include <etl/cmath.hpp>
+#include <etl/concepts.hpp>
+#include <etl/random.hpp>
+
+namespace grit {
+
+template<etl::floating_point Float, typename URNG = etl::xoshiro128plusplus>
+struct AirWindowsVinylDither
+{
+    using value_type = Float;
+    using seed_type  = typename URNG::result_type;
+
+    AirWindowsVinylDither() = default;
+    explicit AirWindowsVinylDither(seed_type seed);
+
+    auto setDeRez(Float deRez) -> void;
+    [[nodiscard]] auto getDeRez() const -> Float;
+
+    [[nodiscard]] auto operator()(Float x) -> Float;
+    auto reset() -> void;
+
+private:
+    auto advanceNoise() -> Float;
+
+    Float _deRez{0};
+    Float _inScale{0};
+    Float _outScale{0};
+
+    URNG _rng{42};
+    etl::uniform_real_distribution<Float> _dist{Float(-0.5), Float(0.5)};
+
+    Float _nsOdd{0};
+    Float _prev{0};
+    etl::array<Float, 16> _ns{};
+};
+
+template<etl::floating_point Float, typename URNG>
+AirWindowsVinylDither<Float, URNG>::AirWindowsVinylDither(seed_type seed) : _rng{seed}
+{}
+
+template<etl::floating_point Float, typename URNG>
+auto AirWindowsVinylDither<Float, URNG>::setDeRez(Float deRez) -> void
+{
+    _deRez = deRez;
+
+    auto scaleFactor = Float(32768.0);
+    if (deRez > Float(0)) {
+        scaleFactor *= etl::pow(Float(1) - deRez, Float(6));
+    }
+    if (scaleFactor < Float(0.0001)) {
+        scaleFactor = Float(0.0001);
+    }
+
+    auto outScale = scaleFactor;
+    if (outScale < Float(8)) {
+        outScale = Float(8);
+    }
+
+    _inScale  = scaleFactor;
+    _outScale = Float(1) / outScale;
+}
+
+template<etl::floating_point Float, typename URNG>
+auto AirWindowsVinylDither<Float, URNG>::getDeRez() const -> Float
+{
+    return _deRez;
+}
+
+template<etl::floating_point Float, typename URNG>
+auto AirWindowsVinylDither<Float, URNG>::operator()(Float x) -> Float
+{
+    auto const y = x * _inScale;
+
+    auto absSample = advanceNoise();
+    absSample += y;
+
+    if (_nsOdd > 0) {
+        _nsOdd -= Float(0.97);
+    }
+    if (_nsOdd < 0) {
+        _nsOdd += Float(0.97);
+    }
+
+    _nsOdd -= (_nsOdd * _nsOdd * _nsOdd * Float(0.475));
+    _nsOdd += _prev;
+
+    absSample += (_nsOdd * Float(0.475));
+    auto const floor = etl::floor(absSample);
+
+    _prev = floor - y;
+    return floor * _outScale;
+}
+
+template<etl::floating_point Float, typename URNG>
+auto AirWindowsVinylDither<Float, URNG>::reset() -> void
+{
+    _nsOdd = Float(0);
+    _prev  = Float(0);
+    etl::fill(_ns.begin(), _ns.end(), Float(0));
+}
+
+template<etl::floating_point Float, typename URNG>
+auto AirWindowsVinylDither<Float, URNG>::advanceNoise() -> Float
+{
+    auto absSample = _dist(_rng);
+    _ns[0] += absSample;
+    _ns[0] *= Float(0.5);
+    absSample -= _ns[0];
+
+    for (auto i{1U}; i < _ns.size(); ++i) {
+        absSample += _dist(_rng);
+        _ns[i] += absSample;
+        _ns[i] *= Float(0.5);
+        absSample -= _ns[i];
+    }
+
+    return absSample;
+}
+
+}  // namespace grit

lib/grit/audio/noise/airwindows_vinyl_dither_test.cpp

@@ -0,0 +1,19 @@
+#include "airwindows_vinyl_dither.hpp"
+
+#include <catch2/catch_approx.hpp>
+#include <catch2/catch_template_test_macros.hpp>
+
+TEMPLATE_TEST_CASE("grit/audio/noise: AirWindowsVinylDither", "", float, double)
+{
+    using Float = TestType;
+
+    auto proc = grit::AirWindowsVinylDither<Float>{42};
+    proc.reset();
+    REQUIRE(proc(Float(0.0)) == Catch::Approx(Float(0.0)));
+
+    proc.setDeRez(Float(0.5));
+    REQUIRE(proc.getDeRez() == Catch::Approx(Float(0.5)));
+    REQUIRE(proc(Float(0.125)) != Float(0.0));
+    REQUIRE(proc(Float(0.111)) != Float(0.0));
+    REQUIRE(proc(Float(0.113)) != Float(0.0));
+}

lib/grit/audio/noise/dither_test.cpp

@@ -6,7 +6,7 @@
 #include <random>
 
 TEMPLATE_PRODUCT_TEST_CASE(
-    "grit/audio/dither:",
+    "grit/audio/noise: Dither",
     "",
     (grit::NoDither, grit::RectangleDither, grit::TriangleDither),
     (etl::xorshift32, etl::xoshiro128plus, std::mt19937)