UnrealEngineUWP/Engine/Source/Runtime/SignalProcessing/Private/DynamicsProcessor.cpp

// Copyright 1998-2019 Epic Games, Inc. All Rights Reserved.

#include "DSP/DynamicsProcessor.h"

namespace Audio
{
	FDynamicsProcessor::FDynamicsProcessor()
		: ProcessingMode(EDynamicsProcessingMode::Compressor)
		, LookaheedDelayMsec(10.0f)
		, AttackTimeMsec(20.0f)
		, ReleaseTimeMsec(1000.0f)
		, ThresholdDb(-6.0f)
		, Ratio(1.0f)
		, HalfKneeBandwidthDb(5.0f)
		, InputGain(1.0f)
		, OutputGain(1.0f)
		, NumChannels(0)
		, bIsChannelLinked(true)
		, bIsAnalogMode(true)
	{
		// The knee will have 2 points
		KneePoints.Init(FVector2D(), 2);
	}

	FDynamicsProcessor::~FDynamicsProcessor()
	{
	}

	void FDynamicsProcessor::Init(const float SampleRate, const int32 InNumChannels)
	{
		NumChannels = InNumChannels;
		for (int32 Channel = 0; Channel < InNumChannels; ++Channel)
		{
			int32 Index = LookaheadDelay.Add(FDelay());
			LookaheadDelay[Index].Init(SampleRate, 0.1f);
			LookaheadDelay[Index].SetDelayMsec(LookaheedDelayMsec);

			Index = EnvFollower.Add(FEnvelopeFollower());
			EnvFollower[Index].Init(SampleRate, AttackTimeMsec, ReleaseTimeMsec, EPeakMode::RootMeanSquared, bIsAnalogMode);
		}
	}

	void FDynamicsProcessor::SetLookaheadMsec(const float InLookAheadMsec)
	{
		LookaheedDelayMsec = InLookAheadMsec;
		for (int32 Channel = 0; Channel < LookaheadDelay.Num(); ++Channel)
		{
			LookaheadDelay[Channel].SetDelayMsec(LookaheedDelayMsec);
		}
	}

	void FDynamicsProcessor::SetAttackTime(const float InAttackTimeMsec)
	{
		AttackTimeMsec = InAttackTimeMsec;
		for (int32 Channel = 0; Channel < EnvFollower.Num(); ++Channel)
		{
			EnvFollower[Channel].SetAttackTime(InAttackTimeMsec);
		}
	}

	void FDynamicsProcessor::SetReleaseTime(const float InReleaseTimeMsec)
	{
		ReleaseTimeMsec = InReleaseTimeMsec;
		for (int32 Channel = 0; Channel < EnvFollower.Num(); ++Channel)
		{
			EnvFollower[Channel].SetReleaseTime(InReleaseTimeMsec);
		}
	}

	void FDynamicsProcessor::SetThreshold(const float InThresholdDb)
	{
		ThresholdDb = InThresholdDb;
	}

	void FDynamicsProcessor::SetRatio(const float InCompressionRatio)
	{
		// Don't let the compression ratio be 0.0!
		Ratio = FMath::Max(InCompressionRatio, SMALL_NUMBER);
	}

	void FDynamicsProcessor::SetKneeBandwidth(const float InKneeBandwidthDb)
	{
		HalfKneeBandwidthDb = 0.5f * InKneeBandwidthDb;
	}

	void FDynamicsProcessor::SetInputGain(const float InInputGainDb)
	{
		InputGain = ConvertToLinear(InInputGainDb);
	}

	void FDynamicsProcessor::SetOutputGain(const float InOutputGainDb)
	{
		OutputGain = ConvertToLinear(InOutputGainDb);
	}

	void FDynamicsProcessor::SetChannelLinked(const bool bInIsChannelLinked)
	{
		bIsChannelLinked = bInIsChannelLinked;
	}

	void FDynamicsProcessor::SetAnalogMode(const bool bInIsAnalogMode)
	{
		bIsAnalogMode = bInIsAnalogMode;
		for (int32 Channel = 0; Channel < EnvFollower.Num(); ++Channel)
		{
			EnvFollower[Channel].SetAnalog(bInIsAnalogMode);
		}
	}

	void FDynamicsProcessor::SetPeakMode(const EPeakMode::Type InEnvelopeFollowerModeType)
	{
		for (int32 Channel = 0; Channel < EnvFollower.Num(); ++Channel)
		{
			EnvFollower[Channel].SetMode(InEnvelopeFollowerModeType);
		}
	}

	void FDynamicsProcessor::SetProcessingMode(const EDynamicsProcessingMode::Type InProcessingMode)
	{
		ProcessingMode = InProcessingMode;
	}

	void FDynamicsProcessor::ProcessAudioFrame(const float* InFrame, float* OutFrame)
	{
		// Get detector outputs
		DetectorOuts.Reset();
		 
		for (int32 Channel = 0; Channel < NumChannels; ++Channel)
		{
			DetectorOuts.Add(EnvFollower[Channel].ProcessAudio(InputGain * InFrame[Channel]));
		}

		Gain.Reset();

		if (bIsChannelLinked)
		{
			// average all channels
			float DetectorOutLinked = 0.0f;
			for (int32 Channel = 0; Channel < NumChannels; ++Channel)
			{
				DetectorOutLinked += DetectorOuts[Channel];
			}
			DetectorOutLinked /= (float)NumChannels;

			// convert to decibels
			const float DetectorOutLinkedDb = ConvertToDecibels(DetectorOutLinked);

			const float ComputedGain = ComputeGain(DetectorOutLinkedDb);

			for (int32 Channel = 0; Channel < NumChannels; ++Channel)
			{
				Gain.Add(ComputedGain);
			}
		}
		else
		{
			// compute gain individually per channel
			for (int32 Channel = 0; Channel < NumChannels; ++Channel)
			{
				// convert to decibels
				const float DetectorOutLinkedDb = ConvertToDecibels(DetectorOuts[Channel]);

				const float ComputedGain = ComputeGain(DetectorOutLinkedDb);

				Gain.Add(ComputedGain);
			}
		}

		for (int32 Channel = 0; Channel < NumChannels; ++Channel)
		{
			// Write and read into the look ahead delay line.
			// We apply the compression output of the direct input to the output of this delay line
			// This way sharp transients can be "caught" with the gain.
			float LookaheadOutput = LookaheadDelay[Channel].ProcessAudioSample(InFrame[Channel]);

			// Write into the output with the computed gain value
			OutFrame[Channel] = Gain[Channel] * LookaheadOutput * OutputGain * InputGain;
		}
	}

	void FDynamicsProcessor::ProcessAudio(const float* InBuffer, const int32 InNumSamples, float* OutBuffer)
	{
		for (int32 SampleIndex = 0; SampleIndex < InNumSamples; SampleIndex += NumChannels)
		{
			ProcessAudioFrame(&InBuffer[SampleIndex], &OutBuffer[SampleIndex]);
		}
	}

	float FDynamicsProcessor::ComputeGain(const float InEnvFollowerDb)
	{
		float SlopeFactor = 0.0f;

		// Depending on the mode, we define the "slope". 
		switch (ProcessingMode)
		{
			default:

			// Compressors smoothly reduce the gain as the gain gets louder
			// CompressionRatio -> Inifinity is a limiter
			case EDynamicsProcessingMode::Compressor:
				SlopeFactor = 1.0f - 1.0f / Ratio;
				break;

			// Limiters do nothing until it hits the threshold then clamps the output hard
			case EDynamicsProcessingMode::Limiter:
				SlopeFactor = 1.0f;
				break;

			// Expanders smoothly increase the gain as the gain gets louder
			// CompressionRatio -> Infinity is a gate
			case EDynamicsProcessingMode::Expander:
				SlopeFactor = 1.0f / Ratio - 1.0f;
				break;

			// Gates are opposite of limiter. They stop sound (stop gain) until the threshold is hit
			case EDynamicsProcessingMode::Gate:
				SlopeFactor = -1.0f;
				break;
		}

		// If we are in the range of compression
		if (HalfKneeBandwidthDb > 0.0f && InEnvFollowerDb > (ThresholdDb - HalfKneeBandwidthDb) && InEnvFollowerDb < ThresholdDb + HalfKneeBandwidthDb)
		{
			// Setup the knee for interpolation. Don't allow the top knee point to exceed 0.0
			KneePoints[0].X = ThresholdDb - HalfKneeBandwidthDb;
			KneePoints[1].X = FMath::Min(ThresholdDb + HalfKneeBandwidthDb, 0.0f);

			KneePoints[0].Y = 0.0f;
			KneePoints[1].Y = SlopeFactor;

			// The knee calculation adjusts the slope to use via lagrangian interpolation through the slope
			SlopeFactor = LagrangianInterpolation(KneePoints, InEnvFollowerDb);
		}

		float OutputGainDb = SlopeFactor * (ThresholdDb - InEnvFollowerDb);
		OutputGainDb = FMath::Min(0.0f, OutputGainDb);
		return ConvertToLinear(OutputGainDb);
	}


}