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Diffstat (limited to 'audio/softsynth/mt32/srchelper/srctools/include/IIR2xResampler.h')
-rw-r--r-- | audio/softsynth/mt32/srchelper/srctools/include/IIR2xResampler.h | 100 |
1 files changed, 100 insertions, 0 deletions
diff --git a/audio/softsynth/mt32/srchelper/srctools/include/IIR2xResampler.h b/audio/softsynth/mt32/srchelper/srctools/include/IIR2xResampler.h new file mode 100644 index 0000000000..23733e4049 --- /dev/null +++ b/audio/softsynth/mt32/srchelper/srctools/include/IIR2xResampler.h @@ -0,0 +1,100 @@ +/* Copyright (C) 2015-2017 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 IIR_2X_RESAMPLER_H +#define IIR_2X_RESAMPLER_H + +#include "ResamplerStage.h" + +namespace SRCTools { + +static const unsigned int IIR_RESAMPER_CHANNEL_COUNT = 2; +static const unsigned int IIR_SECTION_ORDER = 2; + +typedef FloatSample IIRCoefficient; +typedef FloatSample BufferedSample; + +typedef BufferedSample SectionBuffer[IIR_SECTION_ORDER]; + +// Non-trivial coefficients of a 2nd-order section of a parallel bank +// (zero-order numerator coefficient is always zero, zero-order denominator coefficient is always unity) +struct IIRSection { + IIRCoefficient num1; + IIRCoefficient num2; + IIRCoefficient den1; + IIRCoefficient den2; +}; + +class IIRResampler : public ResamplerStage { +public: + enum Quality { + // Used when providing custom IIR filter coefficients. + CUSTOM, + // Use fast elliptic filter with symmetric ripple: N=8, Ap=As=-99 dB, fp=0.125, fs = 0.25 (in terms of sample rate) + FAST, + // Use average elliptic filter with symmetric ripple: N=12, Ap=As=-106 dB, fp=0.193, fs = 0.25 (in terms of sample rate) + GOOD, + // Use sharp elliptic filter with symmetric ripple: N=18, Ap=As=-106 dB, fp=0.238, fs = 0.25 (in terms of sample rate) + BEST + }; + + // Returns the retained fraction of the passband for the given standard quality value + static double getPassbandFractionForQuality(Quality quality); + +protected: + explicit IIRResampler(const Quality quality); + explicit IIRResampler(const unsigned int useSectionsCount, const IIRCoefficient useFIR, const IIRSection useSections[]); + ~IIRResampler(); + + const struct Constants { + // Coefficient of the 0-order FIR part + IIRCoefficient fir; + // 2nd-order sections that comprise a parallel bank + const IIRSection *sections; + // Number of 2nd-order sections + unsigned int sectionsCount; + // Delay line per channel per section + SectionBuffer *buffer; + + Constants(const unsigned int useSectionsCount, const IIRCoefficient useFIR, const IIRSection useSections[], const Quality quality); + } constants; +}; // class IIRResampler + +class IIR2xInterpolator : public IIRResampler { +public: + explicit IIR2xInterpolator(const Quality quality); + explicit IIR2xInterpolator(const unsigned int useSectionsCount, const IIRCoefficient useFIR, const IIRSection useSections[]); + + void process(const FloatSample *&inSamples, unsigned int &inLength, FloatSample *&outSamples, unsigned int &outLength); + unsigned int estimateInLength(const unsigned int outLength) const; + +private: + FloatSample lastInputSamples[IIR_RESAMPER_CHANNEL_COUNT]; + unsigned int phase; +}; + +class IIR2xDecimator : public IIRResampler { +public: + explicit IIR2xDecimator(const Quality quality); + explicit IIR2xDecimator(const unsigned int useSectionsCount, const IIRCoefficient useFIR, const IIRSection useSections[]); + + void process(const FloatSample *&inSamples, unsigned int &inLength, FloatSample *&outSamples, unsigned int &outLength); + unsigned int estimateInLength(const unsigned int outLength) const; +}; + +} // namespace SRCTools + +#endif // IIR_2X_RESAMPLER_H |