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audio/softsynth/mt32/srchelper/srctools/include/ResamplerModel.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 SRCTOOLS_RESAMPLER_MODEL_H
+#define SRCTOOLS_RESAMPLER_MODEL_H
+
+#include "FloatSampleProvider.h"
+
+namespace SRCTools {
+
+class ResamplerStage;
+
+/** Model consists of one or more ResampleStage instances connected in a cascade. */
+namespace ResamplerModel {
+
+// Seems to be a good choice for 16-bit integer samples.
+static const double DEFAULT_DB_SNR = 106;
+
+// When using linear interpolation, oversampling factor necessary to achieve the DEFAULT_DB_SNR is about 256.
+// This figure is the upper estimation, and it can be found by analysing the frequency response of the linear interpolator.
+// When less SNR is desired, this value should also decrease in accordance.
+static const unsigned int DEFAULT_WINDOWED_SINC_MAX_DOWNSAMPLE_FACTOR = 256;
+
+// In the default resampler model, the input to the windowed sinc filter is always at least 2x oversampled during upsampling,
+// so oversampling factor of 128 should be sufficient to achieve the DEFAULT_DB_SNR with linear interpolation.
+static const unsigned int DEFAULT_WINDOWED_SINC_MAX_UPSAMPLE_FACTOR = DEFAULT_WINDOWED_SINC_MAX_DOWNSAMPLE_FACTOR / 2;
+
+
+enum Quality {
+	// Use when the speed is more important than the audio quality.
+	FASTEST,
+	// Use FAST quality setting of the IIR stage (50% of passband retained).
+	FAST,
+	// Use GOOD quality setting of the IIR stage (77% of passband retained).
+	GOOD,
+	// Use BEST quality setting of the IIR stage (95% of passband retained).
+	BEST
+};
+
+FloatSampleProvider &createResamplerModel(FloatSampleProvider &source, double sourceSampleRate, double targetSampleRate, Quality quality);
+FloatSampleProvider &createResamplerModel(FloatSampleProvider &source, ResamplerStage **stages, unsigned int stageCount);
+FloatSampleProvider &createResamplerModel(FloatSampleProvider &source, ResamplerStage &stage);
+
+void freeResamplerModel(FloatSampleProvider &model, FloatSampleProvider &source);
+
+} // namespace ResamplerModel
+
+} // namespace SRCTools
+
+#endif // SRCTOOLS_RESAMPLER_MODEL_H