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audio/softsynth/mt32/srchelper/InternalResampler.cpp

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+/* Copyright (C) 2015-2022 Sergey V. Mikayev
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU Lesser General Public License as published by
+ *  the Free Software Foundation, either version 2.1 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program 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 Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "InternalResampler.h"
+
+#include "srctools/include/SincResampler.h"
+#include "srctools/include/ResamplerModel.h"
+
+#include "../Synth.h"
+
+using namespace SRCTools;
+
+namespace MT32Emu {
+
+class SynthWrapper : public FloatSampleProvider {
+	Synth &synth;
+
+public:
+	SynthWrapper(Synth &useSynth) : synth(useSynth)
+	{}
+
+	void getOutputSamples(FloatSample *outBuffer, unsigned int size) {
+		synth.render(outBuffer, size);
+	}
+};
+
+static FloatSampleProvider &createModel(Synth &synth, SRCTools::FloatSampleProvider &synthSource, double targetSampleRate, SamplerateConversionQuality quality) {
+	static const double MAX_AUDIBLE_FREQUENCY = 20000.0;
+
+	const double sourceSampleRate = synth.getStereoOutputSampleRate();
+	if (quality != SamplerateConversionQuality_FASTEST) {
+		const bool oversampledMode = synth.getStereoOutputSampleRate() == Synth::getStereoOutputSampleRate(AnalogOutputMode_OVERSAMPLED);
+		// Oversampled input allows to bypass IIR interpolation stage and, in some cases, IIR decimation stage
+		if (oversampledMode && (0.5 * sourceSampleRate) <= targetSampleRate) {
+			// NOTE: In the oversampled mode, the transition band starts at 20kHz and ends at 28kHz
+			double passband = MAX_AUDIBLE_FREQUENCY;
+			double stopband = 0.5 * sourceSampleRate + MAX_AUDIBLE_FREQUENCY;
+			ResamplerStage &resamplerStage = *SincResampler::createSincResampler(sourceSampleRate, targetSampleRate, passband, stopband, ResamplerModel::DEFAULT_DB_SNR, ResamplerModel::DEFAULT_WINDOWED_SINC_MAX_UPSAMPLE_FACTOR);
+			return ResamplerModel::createResamplerModel(synthSource, resamplerStage);
+		}
+	}
+	return ResamplerModel::createResamplerModel(synthSource, sourceSampleRate, targetSampleRate, static_cast<ResamplerModel::Quality>(quality));
+}
+
+} // namespace MT32Emu
+
+using namespace MT32Emu;
+
+InternalResampler::InternalResampler(Synth &synth, double targetSampleRate, SamplerateConversionQuality quality) :
+	synthSource(*new SynthWrapper(synth)),
+	model(createModel(synth, synthSource, targetSampleRate, quality))
+{}
+
+InternalResampler::~InternalResampler() {
+	ResamplerModel::freeResamplerModel(model, synthSource);
+	delete &synthSource;
+}
+
+void InternalResampler::getOutputSamples(float *buffer, unsigned int length) {
+	model.getOutputSamples(buffer, length);
+}