Spc_Filter.h

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// Simple low-pass and high-pass filter to better match sound output of a SNES
 
// Game_Music_Emu https://bitbucket.org/mpyne/game-music-emu/
#ifndef SPC_FILTER_H
#define SPC_FILTER_H
 
#include "blargg_common.h"
 
struct SPC_Filter {
public:
        
        // Filters count samples of stereo sound in place. Count must be a multiple of 2.
        typedef short sample_t;
        void run( sample_t* io, int count );
        
// Optional features
 
        // Clears filter to silence
        void clear();
        
        // Sets gain (volume), where gain_unit is normal. Gains greater than gain_unit
        // are fine, since output is clamped to 16-bit sample range.
        enum { gain_unit = 0x100 };
        void set_gain( int gain );
        
        // Enables/disables filtering (when disabled, gain is still applied)
        void enable( bool b );
        
        // Sets amount of bass (logarithmic scale)
        enum { bass_none =  0 };
        enum { bass_norm =  8 }; // normal amount
        enum { bass_max  = 31 };
        void set_bass( int bass );
        
public:
        SPC_Filter();
        BLARGG_DISABLE_NOTHROW
private:
        enum { gain_bits = 8 };
        int gain;
        int bass;
        bool enabled;
        struct chan_t { int p1, pp1, sum; };
        chan_t ch [2];
};
 
inline void SPC_Filter::enable( bool b )  { enabled = b; }
 
inline void SPC_Filter::set_gain( int g ) { gain = g; }
 
inline void SPC_Filter::set_bass( int b ) { bass = b; }
 
#endif