OpenAL32/Include/alFilter.h

   1 #ifndef _AL_FILTER_H_
   2 #define _AL_FILTER_H_
   3
   4 #include "alMain.h"
   5
   6 #include "math_defs.h"
   7
   8 #ifdef __cplusplus
   9 extern "C" {
  10 #endif
  11
  12 #define LOWPASSFREQREF  (5000.0f)
  13 #define HIGHPASSFREQREF  (250.0f)
  14
  15
  16 /* Filters implementation is based on the "Cookbook formulae for audio
  17  * EQ biquad filter coefficients" by Robert Bristow-Johnson
  18  * http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt
  19  */
  20 /* Implementation note: For the shelf filters, the specified gain is for the
  21  * reference frequency, which is the centerpoint of the transition band. This
  22  * better matches EFX filter design. To set the gain for the shelf itself, use
  23  * the square root of the desired linear gain (or halve the dB gain).
  24  */
  25
  26 typedef enum ALfilterType {
  27     /** EFX-style low-pass filter, specifying a gain and reference frequency. */
  28     ALfilterType_HighShelf,
  29     /** EFX-style high-pass filter, specifying a gain and reference frequency. */
  30     ALfilterType_LowShelf,
  31     /** Peaking filter, specifying a gain and reference frequency. */
  32     ALfilterType_Peaking,
  33
  34     /** Low-pass cut-off filter, specifying a cut-off frequency. */
  35     ALfilterType_LowPass,
  36     /** High-pass cut-off filter, specifying a cut-off frequency. */
  37     ALfilterType_HighPass,
  38     /** Band-pass filter, specifying a center frequency. */
  39     ALfilterType_BandPass,
  40 } ALfilterType;
  41
  42 typedef struct ALfilterState {
  43     ALfloat x[2]; /* History of two last input samples  */
  44     ALfloat y[2]; /* History of two last output samples */
  45     ALfloat a1, a2; /* Transfer function coefficients "a" (a0 is pre-applied) */
  46     ALfloat b1, b2; /* Transfer function coefficients "b" (b0 is input_gain) */
  47     ALfloat input_gain;
  48
  49     void (*process)(struct ALfilterState *self, ALfloat *restrict dst, const ALfloat *src, ALuint numsamples);
  50 } ALfilterState;
  51 #define ALfilterState_process(a, ...) ((a)->process((a), __VA_ARGS__))
  52
  53 /* Calculates the rcpQ (i.e. 1/Q) coefficient for shelving filters, using the
  54  * reference gain and shelf slope parameter.
  55  * 0 < gain
  56  * 0 < slope <= 1
  57  */
  58 inline ALfloat calc_rcpQ_from_slope(ALfloat gain, ALfloat slope)
  59 {
  60     return sqrtf((gain + 1.0f/gain)*(1.0f/slope - 1.0f) + 2.0f);
  61 }
  62 /* Calculates the rcpQ (i.e. 1/Q) coefficient for filters, using the frequency
  63  * multiple (i.e. ref_freq / sampling_freq) and bandwidth.
  64  * 0 < freq_mult < 0.5.
  65  */
  66 inline ALfloat calc_rcpQ_from_bandwidth(ALfloat freq_mult, ALfloat bandwidth)
  67 {
  68     ALfloat w0 = F_TAU * freq_mult;
  69     return 2.0f*sinhf(logf(2.0f)/2.0f*bandwidth*w0/sinf(w0));
  70 }
  71
  72 inline void ALfilterState_clear(ALfilterState *filter)
  73 {
  74     filter->x[0] = 0.0f;
  75     filter->x[1] = 0.0f;
  76     filter->y[0] = 0.0f;
  77     filter->y[1] = 0.0f;
  78 }
  79
  80 void ALfilterState_setParams(ALfilterState *filter, ALfilterType type, ALfloat gain, ALfloat freq_mult, ALfloat rcpQ);
  81
  82 inline ALfloat ALfilterState_processSingle(ALfilterState *filter, ALfloat sample)
  83 {
  84     ALfloat outsmp;
  85
  86     outsmp = filter->input_gain * sample +
  87              filter->b1 * filter->x[0] +
  88              filter->b2 * filter->x[1] -
  89              filter->a1 * filter->y[0] -
  90              filter->a2 * filter->y[1];
  91     filter->x[1] = filter->x[0];
  92     filter->x[0] = sample;
  93     filter->y[1] = filter->y[0];
  94     filter->y[0] = outsmp;
  95
  96     return outsmp;
  97 }
  98
  99 void ALfilterState_processC(ALfilterState *filter, ALfloat *restrict dst, const ALfloat *src, ALuint numsamples);
 100
 101 inline void ALfilterState_processPassthru(ALfilterState *filter, const ALfloat *src, ALuint numsamples)
 102 {
 103     if(numsamples >= 2)
 104     {
 105         filter->x[1] = src[numsamples-2];
 106         filter->x[0] = src[numsamples-1];
 107         filter->y[1] = src[numsamples-2];
 108         filter->y[0] = src[numsamples-1];
 109     }
 110     else if(numsamples == 1)
 111     {
 112         filter->x[1] = filter->x[0];
 113         filter->x[0] = src[0];
 114         filter->y[1] = filter->y[0];
 115         filter->y[0] = src[0];
 116     }
 117 }
 118
 119
 120 typedef struct ALfilter {
 121     // Filter type (AL_FILTER_NULL, ...)
 122     ALenum type;
 123
 124     ALfloat Gain;
 125     ALfloat GainHF;
 126     ALfloat HFReference;
 127     ALfloat GainLF;
 128     ALfloat LFReference;
 129
 130     void (*SetParami)(struct ALfilter *filter, ALCcontext *context, ALenum param, ALint val);
 131     void (*SetParamiv)(struct ALfilter *filter, ALCcontext *context, ALenum param, const ALint *vals);
 132     void (*SetParamf)(struct ALfilter *filter, ALCcontext *context, ALenum param, ALfloat val);
 133     void (*SetParamfv)(struct ALfilter *filter, ALCcontext *context, ALenum param, const ALfloat *vals);
 134
 135     void (*GetParami)(struct ALfilter *filter, ALCcontext *context, ALenum param, ALint *val);
 136     void (*GetParamiv)(struct ALfilter *filter, ALCcontext *context, ALenum param, ALint *vals);
 137     void (*GetParamf)(struct ALfilter *filter, ALCcontext *context, ALenum param, ALfloat *val);
 138     void (*GetParamfv)(struct ALfilter *filter, ALCcontext *context, ALenum param, ALfloat *vals);
 139
 140     /* Self ID */
 141     ALuint id;
 142 } ALfilter;
 143
 144 #define ALfilter_SetParami(x, c, p, v)  ((x)->SetParami((x),(c),(p),(v)))
 145 #define ALfilter_SetParamiv(x, c, p, v) ((x)->SetParamiv((x),(c),(p),(v)))
 146 #define ALfilter_SetParamf(x, c, p, v)  ((x)->SetParamf((x),(c),(p),(v)))
 147 #define ALfilter_SetParamfv(x, c, p, v) ((x)->SetParamfv((x),(c),(p),(v)))
 148
 149 #define ALfilter_GetParami(x, c, p, v)  ((x)->GetParami((x),(c),(p),(v)))
 150 #define ALfilter_GetParamiv(x, c, p, v) ((x)->GetParamiv((x),(c),(p),(v)))
 151 #define ALfilter_GetParamf(x, c, p, v)  ((x)->GetParamf((x),(c),(p),(v)))
 152 #define ALfilter_GetParamfv(x, c, p, v) ((x)->GetParamfv((x),(c),(p),(v)))
 153
 154 inline struct ALfilter *LookupFilter(ALCdevice *device, ALuint id)
 155 { return (struct ALfilter*)LookupUIntMapKey(&device->FilterMap, id); }
 156 inline struct ALfilter *RemoveFilter(ALCdevice *device, ALuint id)
 157 { return (struct ALfilter*)RemoveUIntMapKey(&device->FilterMap, id); }
 158
 159 ALvoid ReleaseALFilters(ALCdevice *device);
 160
 161 #ifdef __cplusplus
 162 }
 163 #endif
 164
 165 #endif