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audio/softsynth/mt32/SampleRateConverter.h

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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/>.
+ */
+
+#ifndef MT32EMU_SAMPLE_RATE_CONVERTER_H
+#define MT32EMU_SAMPLE_RATE_CONVERTER_H
+
+#include "globals.h"
+#include "Types.h"
+#include "Enumerations.h"
+
+namespace MT32Emu {
+
+class Synth;
+
+/* SampleRateConverter class allows to convert the synthesiser output to any desired sample rate.
+ * It processes the completely mixed stereo output signal as it passes the analogue circuit emulation,
+ * so emulating the synthesiser output signal passing further through an ADC.
+ * Several conversion quality options are provided which allow to trade-off the conversion speed vs. the passband width.
+ * All the options except FASTEST guarantee full suppression of the aliasing noise in terms of the 16-bit integer samples.
+ */
+class MT32EMU_EXPORT SampleRateConverter {
+public:
+	// Returns the value of AnalogOutputMode for which the output signal may retain its full frequency spectrum
+	// at the sample rate specified by the targetSampleRate argument.
+	static AnalogOutputMode getBestAnalogOutputMode(double targetSampleRate);
+
+	// Returns the sample rate supported by the sample rate conversion implementation currently in effect
+	// that is closest to the one specified by the desiredSampleRate argument.
+	static double getSupportedOutputSampleRate(double desiredSampleRate);
+
+	// Creates a SampleRateConverter instance that converts output signal from the synth to the given sample rate
+	// with the specified conversion quality.
+	SampleRateConverter(Synth &synth, double targetSampleRate, SamplerateConversionQuality quality);
+	~SampleRateConverter();
+
+	// Fills the provided output buffer with the results of the sample rate conversion.
+	// The input samples are automatically retrieved from the synth as necessary.
+	void getOutputSamples(MT32Emu::Bit16s *buffer, unsigned int length);
+
+	// Fills the provided output buffer with the results of the sample rate conversion.
+	// The input samples are automatically retrieved from the synth as necessary.
+	void getOutputSamples(float *buffer, unsigned int length);
+
+	// Returns the number of samples produced at the internal synth sample rate (32000 Hz)
+	// that correspond to the number of samples at the target sample rate.
+	// Intended to facilitate audio time synchronisation.
+	double convertOutputToSynthTimestamp(double outputTimestamp) const;
+
+	// Returns the number of samples produced at the target sample rate
+	// that correspond to the number of samples at the internal synth sample rate (32000 Hz).
+	// Intended to facilitate audio time synchronisation.
+	double convertSynthToOutputTimestamp(double synthTimestamp) const;
+
+private:
+	const double synthInternalToTargetSampleRateRatio;
+	const bool useSynthDelegate;
+	void * const srcDelegate;
+}; // class SampleRateConverter
+
+} // namespace MT32Emu
+
+#endif // MT32EMU_SAMPLE_RATE_CONVERTER_H