Add audio compressor

libs/audio/include/psemek/audio/effect/compressor.hpp

@@ -0,0 +1,13 @@
+#pragma once
+
+#include <psemek/audio/stream.hpp>
+#include <psemek/audio/constants.hpp>
+
+namespace psemek::audio
+{
+
+	stream_ptr compressor(stream_ptr stream, float volume_threshold = from_db(-1.f), float strength = 0.9f, float envelope_attack = 0.01f, float envelope_release = 1.f);
+
+	stream_ptr limiter(stream_ptr stream, float volume_threshold = from_db(0.f), float envelope_attack = 0.01f, float envelope_release = 1.f);
+
+}

libs/audio/source/effect/compressor.cpp

@@ -0,0 +1,78 @@
+#include <psemek/audio/effect/compressor.hpp>
+#include <psemek/audio/smooth.hpp>
+#include <psemek/geom/math.hpp>
+
+namespace psemek::audio
+{
+
+	namespace
+	{
+
+		struct compressor_impl
+			: stream
+		{
+			compressor_impl(stream_ptr stream, float volume_threshold, float strength, float envelope_attack, float envelope_release)
+				: stream_(std::move(stream))
+				, volume_threshold_log_(std::log(volume_threshold))
+				, strength_(strength)
+				, envelope_attack_multiplier_(smoothness_to_multiplier(envelope_attack))
+				, envelope_release_multiplier_(smoothness_to_multiplier(envelope_release))
+			{}
+
+			std::optional<std::size_t> length() const override
+			{
+				return stream_->length();
+			}
+
+			std::size_t read(float * data, std::size_t sample_count) override
+			{
+				auto result = stream_->read(data, sample_count);
+
+				for (std::size_t i = 0; i < result; i += 2)
+				{
+					float v = std::max(std::abs(data[i]), std::abs(data[i + 1]));
+
+					float multiplier = (v > envelope_) ? envelope_attack_multiplier_ : envelope_release_multiplier_;
+
+					envelope_ += (v - envelope_) * multiplier;
+
+					float strength = strength_;
+
+					float log_gain = strength * std::min(0.f, volume_threshold_log_ - std::log(envelope_));
+
+					float gain = std::exp(log_gain);
+
+					data[i + 0] *= gain;
+					data[i + 1] *= gain;
+				}
+
+				return result;
+			}
+
+			std::size_t played() const override
+			{
+				return stream_->played();
+			}
+
+		private:
+			stream_ptr stream_;
+			float volume_threshold_log_;
+			float strength_;
+			float envelope_attack_multiplier_;
+			float envelope_release_multiplier_;
+			float envelope_ = 0.f;
+		};
+
+	}
+
+	stream_ptr compressor(stream_ptr stream, float volume_threshold, float strength, float envelope_attack, float envelope_release)
+	{
+		return std::make_shared<compressor_impl>(std::move(stream), volume_threshold, strength, envelope_attack, envelope_release);
+	}
+
+	stream_ptr limiter(stream_ptr stream, float volume_threshold, float envelope_attack, float envelope_release)
+	{
+		return compressor(std::move(stream), volume_threshold, 1.f, envelope_attack, envelope_release);
+	}
+
+}