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/* 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
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