dither_impl.h File Reference

#include "config.h"
#include "compat.h"
#include "dither.h"

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Macros
#define	LAP   100

Functions
static float	rand_xorshift32 (uint32_t *seed)
static void	white_noise (float *table, size_t count)
static void	tpdf_noise (float *table, size_t count)
static void	highpass_tpdf_noise (float *table, size_t count)
void	mpg123_noise (float *table, size_t count, enum mpg123_noise_type noisetype)
void	dither_table_init (float *dithertable)

Variables
static const uint32_t	init_seed = 2463534242UL

Macro Definition Documentation

LAP

#define LAP   100

Definition at line 15 of file dither_impl.h.

Function Documentation

dither_table_init()

void dither_table_init

(

float *

dithertable

)

Definition at line 116 of file dither_impl.h.

{
    highpass_tpdf_noise(dithertable, DITHERSIZE);
}

highpass_tpdf_noise()

static void highpass_tpdf_noise ( float *  table, size_t  count  )

static

Definition at line 65 of file dither_impl.h.

{
    size_t i;
    uint32_t seed = init_seed;
    /* Ensure some minimum lap for keeping the high-pass filter circular. */
    size_t lap = count > 2*LAP ? LAP : count/2;
 
    float input_noise;
    float xv[9], yv[9];
 
    for(i=0;i<9;i++)
    {
        xv[i] = yv[i] = 0.0f;
    }
 
    for(i=0;i<count+lap;i++)
    {
        if(i==count) seed=init_seed;
 
        /* generate and add 2 random numbers, to make a TPDF noise distribution */
        input_noise = rand_xorshift32(&seed) + rand_xorshift32(&seed);
 
        /* apply 8th order Chebyshev high-pass IIR filter */
        /* Coefficients are from http://www-users.cs.york.ac.uk/~fisher/mkfilter/trad.html
           Given parameters are: Chebyshev, Highpass, ripple=-1, order=8, samplerate=44100, corner1=19000 */
        xv[0] = xv[1]; xv[1] = xv[2]; xv[2] = xv[3]; xv[3] = xv[4]; xv[4] = xv[5]; xv[5] = xv[6]; xv[6] = xv[7]; xv[7] = xv[8];
        xv[8] = input_noise / 1.382814179e+07;
        yv[0] = yv[1]; yv[1] = yv[2]; yv[2] = yv[3]; yv[3] = yv[4]; yv[4] = yv[5]; yv[5] = yv[6]; yv[6] = yv[7]; yv[7] = yv[8];
        yv[8] = (xv[0] + xv[8]) - 8 * (xv[1] + xv[7]) + 28 * (xv[2] + xv[6])
                - 56 * (xv[3] + xv[5]) + 70 * xv[4]
                + ( -0.6706204984 * yv[0]) + ( -5.3720827038 * yv[1])
                + (-19.0865382480 * yv[2]) + (-39.2831607860 * yv[3])
                + (-51.2308985070 * yv[4]) + (-43.3590135780 * yv[5])
                + (-23.2632305320 * yv[6]) + ( -7.2370122050 * yv[7]);
        if(i>=lap) table[i-lap] = yv[8] * 3.0f;
    }
}

Referenced by dither_table_init(), and mpg123_noise().

mpg123_noise()

void mpg123_noise	(	float *	table,
		size_t	count,
		enum mpg123_noise_type	noisetype
	)

Definition at line 103 of file dither_impl.h.

{
    switch(noisetype)
    {
        case mpg123_white_noise: white_noise(table, count); break;
        case mpg123_tpdf_noise:  tpdf_noise(table, count);  break;
        case mpg123_highpass_tpdf_noise:
            highpass_tpdf_noise(table, count);
        break;
    }
}

rand_xorshift32()

static float rand_xorshift32 ( uint32_t *  seed )

static

Definition at line 22 of file dither_impl.h.

{
    union
    {
        uint32_t i;
        float f;
    } fi;
 
    fi.i = *seed;
    fi.i ^= (fi.i<<13);
    fi.i ^= (fi.i>>17);
    fi.i ^= (fi.i<<5);
    *seed = fi.i;
 
    /* scale the number to [-0.5, 0.5] */
#ifdef IEEE_FLOAT
    fi.i = (fi.i>>9)|0x3f800000;
    fi.f -= 1.5f;
#else
    fi.f = (double)fi.i / 4294967295.0;
    fi.f -= 0.5f;
#endif
    return fi.f;
}

Referenced by highpass_tpdf_noise(), tpdf_noise(), and white_noise().

tpdf_noise()

static void tpdf_noise ( float *  table, size_t  count  )

static

Definition at line 56 of file dither_impl.h.

{
    size_t i;
    uint32_t seed = init_seed;
 
    for(i=0; i<count; ++i)
    table[i] = rand_xorshift32(&seed) + rand_xorshift32(&seed);
}

Referenced by mpg123_noise().

white_noise()

static void white_noise ( float *  table, size_t  count  )

static

Definition at line 47 of file dither_impl.h.

{
    size_t i;
    uint32_t seed = init_seed;
 
    for(i=0; i<count; ++i)
    table[i] = rand_xorshift32(&seed);
}

Referenced by mpg123_noise().

Variable Documentation

init_seed

const uint32_t init_seed = 2463534242UL

static

Definition at line 13 of file dither_impl.h.

Referenced by highpass_tpdf_noise(), tpdf_noise(), and white_noise().