Feature Request: AAX Meters

Audio Plugins
14

OK. You can find an implementation of this on develop. Here is an example of a gain reduction meter in the NoiseGate example. Simply replace the NoiseGate.cpp file with the following contents:

/*
 ==============================================================================

 This file is part of the JUCE library.
 Copyright (c) 2015 - ROLI Ltd.

 Permission is granted to use this software under the terms of either:
 a) the GPL v2 (or any later version)
 b) the Affero GPL v3

 Details of these licenses can be found at: www.gnu.org/licenses

 JUCE is distributed in the hope that it will be useful, but WITHOUT ANY
 WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
 A PARTICULAR PURPOSE.  See the GNU General Public License for more details.

 ------------------------------------------------------------------------------

 To release a closed-source product which uses JUCE, commercial licenses are
 available: visit www.juce.com for more information.

 ==============================================================================
 */

#include "../JuceLibraryCode/JuceHeader.h"
#include "../../GenericEditor.h"

class NoiseGate  : public AudioProcessor
{
public:
	//==============================================================================
	//==============================================================================
	NoiseGate()
		: AudioProcessor (BusesProperties().withInput  ("Input",     AudioChannelSet::stereo())
											 .withOutput ("Output",    AudioChannelSet::stereo())
											 .withInput  ("Sidechain", AudioChannelSet::stereo()))
	{
		addParameter (threshold = new AudioParameterFloat ("threshold", "Threshold", 0.0f, 1.0f, 0.5f));
		addParameter (alpha  = new AudioParameterFloat ("alpha",  "Alpha",   0.0f, 1.0f, 0.8f));
		addParameter (gainReduction = new AudioParameterFloat ("reduction", "Gain Reduction",
															   NormalisableRange<float> (0.0f, 1.0f), 0.0f,
															   "", AudioProcessorParameter::expanderGateGainReductionMeter));
	}

	~NoiseGate() {}

	//==============================================================================
	bool isBusesLayoutSupported (const BusesLayout& layouts) const override
	{
		// the sidechain can take any layout, the main bus needs to be the same on the input and output
		return (layouts.getMainInputChannelSet() == layouts.getMainOutputChannelSet() &&
				(! layouts.getMainInputChannelSet().isDisabled()));
	}

	//==============================================================================
	void prepareToPlay (double /*sampleRate*/, int /*maxBlockSize*/) override { lowPassCoeff = 0.0f; sampleCountDown = 0; }
	void releaseResources() override                                          {}

	void processBlock (AudioSampleBuffer& buffer, MidiBuffer&) override
	{
		AudioSampleBuffer mainInputOutput = getBusBuffer(buffer, true, 0);
		AudioSampleBuffer sideChainInput  = getBusBuffer(buffer, true, 1);

		float alphaCopy = *alpha;
		float thresholdCopy = *threshold;
		float maxReduction = 0.0;

		for (int j = 0; j < buffer.getNumSamples(); ++j)
		{
			float mixedSamples = 0.0f;
			for (int i = 0; i < sideChainInput.getNumChannels(); ++i)
				mixedSamples += sideChainInput.getReadPointer (i) [j];

			mixedSamples /= static_cast<float> (sideChainInput.getNumChannels());
			lowPassCoeff = (alphaCopy * lowPassCoeff) + ((1.0f - alphaCopy) * mixedSamples);

			if (lowPassCoeff >= thresholdCopy)
				sampleCountDown = (int) getSampleRate();

			// very in-effective way of doing this
			for (int i = 0; i < mainInputOutput.getNumChannels(); ++i)
			{
				const float inputSample = *mainInputOutput.getReadPointer (i, j);
				const bool gateIsOpen = (sampleCountDown > 0);

				*mainInputOutput.getWritePointer (i, j) = gateIsOpen ? inputSample : 0.0f;
				maxReduction                            = jmax (maxReduction, gateIsOpen ? 0.0f : std::fabs (inputSample));
			}

			if (sampleCountDown > 0)
				--sampleCountDown;
		}

		gainReduction->setValueNotifyingHost (maxReduction);
	}

	//==============================================================================
	AudioProcessorEditor* createEditor() override            { return new GenericEditor (*this); }
	bool hasEditor() const override                          { return true; }
	const String getName() const override                    { return "NoiseGate"; }
	bool acceptsMidi() const override                        { return false; }
	bool producesMidi() const override                       { return false; }
	double getTailLengthSeconds() const override             { return 0.0; }
	int getNumPrograms() override                            { return 1; }
	int getCurrentProgram() override                         { return 0; }
	void setCurrentProgram (int) override                    {}
	const String getProgramName (int) override               { return ""; }
	void changeProgramName (int, const String&) override     {}
	bool isVST2() const noexcept                             { return (wrapperType == wrapperType_VST); }

	//==============================================================================
	void getStateInformation (MemoryBlock& destData) override
	{
		MemoryOutputStream stream (destData, true);

		stream.writeFloat (*threshold);
		stream.writeFloat (*alpha);
	}

	void setStateInformation (const void* data, int sizeInBytes) override
	{
		MemoryInputStream stream (data, static_cast<size_t> (sizeInBytes), false);

		threshold->setValueNotifyingHost (stream.readFloat());
		alpha->setValueNotifyingHost (stream.readFloat());
	}

	enum
	{
		kVST2MaxChannels = 8
	};

private:
	//==============================================================================
	AudioParameterFloat* threshold;
	AudioParameterFloat* alpha;
	AudioParameterFloat* gainReduction;
	int sampleCountDown;

	float lowPassCoeff;

	//==============================================================================
	JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (NoiseGate)
};

//==============================================================================
// This creates new instances of the plugin..
AudioProcessor* JUCE_CALLTYPE createPluginFilter()
{
	return new NoiseGate();
}
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