83 lines
2.5 KiB
C++
83 lines
2.5 KiB
C++
/*
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* WindowedFIR.h
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* -------------
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* Purpose: FIR resampling code
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* Notes : (currently none)
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* Authors: OpenMPT Devs
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* ModPlug-XMMS Devs
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* The OpenMPT source code is released under the BSD license. Read LICENSE for more details.
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*/
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#pragma once
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#include "openmpt/all/BuildSettings.hpp"
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#include "Mixer.h"
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OPENMPT_NAMESPACE_BEGIN
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/*
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------------------------------------------------------------------------------------------------
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fir interpolation doc,
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(derived from "an engineer's guide to fir digital filters", n.j. loy)
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calculate coefficients for ideal lowpass filter (with cutoff = fc in 0..1 (mapped to 0..nyquist))
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c[-N..N] = (i==0) ? fc : sin(fc*pi*i)/(pi*i)
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then apply selected window to coefficients
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c[-N..N] *= w(0..N)
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with n in 2*N and w(n) being a window function (see loy)
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then calculate gain and scale filter coefs to have unity gain.
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------------------------------------------------------------------------------------------------
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*/
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#ifdef MPT_INTMIXER
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// quantizer scale of window coefs - only required for integer mixing
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inline constexpr int WFIR_QUANTBITS = 15;
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inline constexpr double WFIR_QUANTSCALE = 1 << WFIR_QUANTBITS;
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inline constexpr int WFIR_8SHIFT = (WFIR_QUANTBITS - 8);
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inline constexpr int WFIR_16BITSHIFT = (WFIR_QUANTBITS);
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using WFIR_TYPE = int16;
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#else
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using WFIR_TYPE = mixsample_t;
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#endif // INTMIXER
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// log2(number)-1 of precalculated taps range is [4..12]
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inline constexpr int WFIR_FRACBITS = 12; //10
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inline constexpr int WFIR_LUTLEN = ((1 << (WFIR_FRACBITS + 1)) + 1);
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// number of samples in window
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inline constexpr int WFIR_LOG2WIDTH = 3;
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inline constexpr int WFIR_WIDTH = (1 << WFIR_LOG2WIDTH);
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// cutoff (1.0 == pi/2)
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// wfir type
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enum WFIRType
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{
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WFIR_HANN = 0, // Hann
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WFIR_HAMMING = 1, // Hamming
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WFIR_BLACKMANEXACT = 2, // Blackman Exact
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WFIR_BLACKMAN3T61 = 3, // Blackman 3-Tap 61
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WFIR_BLACKMAN3T67 = 4, // Blackman 3-Tap 67
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WFIR_BLACKMAN4T92 = 5, // Blackman-Harris
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WFIR_BLACKMAN4T74 = 6, // Blackman 4-Tap 74
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WFIR_KAISER4T = 7, // Kaiser a=7.5
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};
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// fir interpolation
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inline constexpr int WFIR_FRACSHIFT = (16 - (WFIR_FRACBITS + 1 + WFIR_LOG2WIDTH));
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inline constexpr int WFIR_FRACMASK = ((((1 << (17 - WFIR_FRACSHIFT)) - 1) & ~(WFIR_WIDTH - 1)));
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inline constexpr int WFIR_FRACHALVE = (1 << (16 - (WFIR_FRACBITS + 2)));
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class CWindowedFIR
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{
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private:
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double coef(int,double,double,int,int);
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public:
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void InitTable(double WFIRCutoff, uint8 WFIRType);
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WFIR_TYPE lut[WFIR_LUTLEN * WFIR_WIDTH];
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};
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OPENMPT_NAMESPACE_END
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