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rockbox/apps/eq.c

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/***************************************************************************
* __________ __ ___.
* Open \______ \ ____ ____ | | _\_ |__ _______ ___
* Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ /
* Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < <
* Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \
* \/ \/ \/ \/ \/
* $Id$
*
* Copyright (C) 2006-2007 Thom Johansen
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
* KIND, either express or implied.
*
****************************************************************************/
#include <inttypes.h>
#include "config.h"
#include "fixedpoint.h"
#include "fracmul.h"
#include "eq.h"
#include "replaygain.h"
/**
* Calculate first order shelving filter. Filter is not directly usable by the
* eq_filter() function.
* @param cutoff shelf midpoint frequency. See eq_pk_coefs for format.
* @param A decibel value multiplied by ten, describing gain/attenuation of
* shelf. Max value is 24 dB.
* @param low true for low-shelf filter, false for high-shelf filter.
* @param c pointer to coefficient storage. Coefficients are s4.27 format.
*/
void filter_shelf_coefs(unsigned long cutoff, long A, bool low, int32_t *c)
{
long sin, cos;
int32_t b0, b1, a0, a1; /* s3.28 */
const long g = get_replaygain_int(A*5) << 4; /* 10^(db/40), s3.28 */
sin = fp_sincos(cutoff/2, &cos);
if (low) {
const int32_t sin_div_g = fp_div(sin, g, 25);
const int32_t sin_g = FRACMUL(sin, g);
cos >>= 3;
b0 = sin_g + cos; /* 0.25 .. 4.10 */
b1 = sin_g - cos; /* -1 .. 3.98 */
a0 = sin_div_g + cos; /* 0.25 .. 4.10 */
a1 = sin_div_g - cos; /* -1 .. 3.98 */
} else {
const int32_t cos_div_g = fp_div(cos, g, 25);
const int32_t cos_g = FRACMUL(cos, g);
sin >>= 3;
b0 = sin + cos_g; /* 0.25 .. 4.10 */
b1 = sin - cos_g; /* -3.98 .. 1 */
a0 = sin + cos_div_g; /* 0.25 .. 4.10 */
a1 = sin - cos_div_g; /* -3.98 .. 1 */
}
const int32_t rcp_a0 = fp_div(1, a0, 57); /* 0.24 .. 3.98, s2.29 */
*c++ = FRACMUL_SHL(b0, rcp_a0, 1); /* 0.063 .. 15.85 */
*c++ = FRACMUL_SHL(b1, rcp_a0, 1); /* -15.85 .. 15.85 */
*c++ = -FRACMUL_SHL(a1, rcp_a0, 1); /* -1 .. 1 */
}
#ifdef HAVE_SW_TONE_CONTROLS
/**
* Calculate second order section filter consisting of one low-shelf and one
* high-shelf section.
* @param cutoff_low low-shelf midpoint frequency. See eq_pk_coefs for format.
* @param cutoff_high high-shelf midpoint frequency.
* @param A_low decibel value multiplied by ten, describing gain/attenuation of
* low-shelf part. Max value is 24 dB.
* @param A_high decibel value multiplied by ten, describing gain/attenuation of
* high-shelf part. Max value is 24 dB.
* @param A decibel value multiplied by ten, describing additional overall gain.
* @param c pointer to coefficient storage. Coefficients are s4.27 format.
*/
void filter_bishelf_coefs(unsigned long cutoff_low, unsigned long cutoff_high,
long A_low, long A_high, long A, int32_t *c)
{
const long g = get_replaygain_int(A*10) << 7; /* 10^(db/20), s0.31 */
int32_t c_ls[3], c_hs[3];
filter_shelf_coefs(cutoff_low, A_low, true, c_ls);
filter_shelf_coefs(cutoff_high, A_high, false, c_hs);
c_ls[0] = FRACMUL(g, c_ls[0]);
c_ls[1] = FRACMUL(g, c_ls[1]);
/* now we cascade the two first order filters to one second order filter
* which can be used by eq_filter(). these resulting coefficients have a
* really wide numerical range, so we use a fixed point format which will
* work for the selected cutoff frequencies (in dsp.c) only.
*/
const int32_t b0 = c_ls[0], b1 = c_ls[1], b2 = c_hs[0], b3 = c_hs[1];
const int32_t a0 = c_ls[2], a1 = c_hs[2];
*c++ = FRACMUL_SHL(b0, b2, 4);
*c++ = FRACMUL_SHL(b0, b3, 4) + FRACMUL_SHL(b1, b2, 4);
*c++ = FRACMUL_SHL(b1, b3, 4);
*c++ = a0 + a1;
*c++ = -FRACMUL_SHL(a0, a1, 4);
}
#endif
/* Coef calculation taken from Audio-EQ-Cookbook.txt by Robert Bristow-Johnson.
* Slightly faster calculation can be done by deriving forms which use tan()
* instead of cos() and sin(), but the latter are far easier to use when doing
* fixed point math, and performance is not a big point in the calculation part.
* All the 'a' filter coefficients are negated so we can use only additions
* in the filtering equation.
*/
/**
* Calculate second order section peaking filter coefficients.
* @param cutoff a value from 0 to 0x80000000, where 0 represents 0 Hz and
* 0x80000000 represents the Nyquist frequency (samplerate/2).
* @param Q Q factor value multiplied by ten. Lower bound is artificially set
* at 0.5.
* @param db decibel value multiplied by ten, describing gain/attenuation at
* peak freq. Max value is 24 dB.
* @param c pointer to coefficient storage. Coefficients are s3.28 format.
*/
void eq_pk_coefs(unsigned long cutoff, unsigned long Q, long db, int32_t *c)
{
long cs;
const long one = 1 << 28; /* s3.28 */
const long A = get_replaygain_int(db*5) << 5; /* 10^(db/40), s2.29 */
const long alpha = fp_sincos(cutoff, &cs)/(2*Q)*10 >> 1; /* s1.30 */
int32_t a0, a1, a2; /* these are all s3.28 format */
int32_t b0, b1, b2;
const long alphadivA = fp_div(alpha, A, 27);
const long alphaA = FRACMUL(alpha, A);
/* possible numerical ranges are in comments by each coef */
b0 = one + alphaA; /* [1 .. 5] */
b1 = a1 = -2*(cs >> 3); /* [-2 .. 2] */
b2 = one - alphaA; /* [-3 .. 1] */
a0 = one + alphadivA; /* [1 .. 5] */
a2 = one - alphadivA; /* [-3 .. 1] */
/* range of this is roughly [0.2 .. 1], but we'll never hit 1 completely */
const long rcp_a0 = fp_div(1, a0, 59); /* s0.31 */
*c++ = FRACMUL(b0, rcp_a0); /* [0.25 .. 4] */
*c++ = FRACMUL(b1, rcp_a0); /* [-2 .. 2] */
*c++ = FRACMUL(b2, rcp_a0); /* [-2.4 .. 1] */
*c++ = FRACMUL(-a1, rcp_a0); /* [-2 .. 2] */
*c++ = FRACMUL(-a2, rcp_a0); /* [-0.6 .. 1] */
}
/**
* Calculate coefficients for lowshelf filter. Parameters are as for
* eq_pk_coefs, but the coefficient format is s5.26 fixed point.
*/
void eq_ls_coefs(unsigned long cutoff, unsigned long Q, long db, int32_t *c)
{
long cs;
const long one = 1 << 25; /* s6.25 */
const long sqrtA = get_replaygain_int(db*5/2) << 2; /* 10^(db/80), s5.26 */
const long A = FRACMUL_SHL(sqrtA, sqrtA, 8); /* s2.29 */
const long alpha = fp_sincos(cutoff, &cs)/(2*Q)*10 >> 1; /* s1.30 */
const long ap1 = (A >> 4) + one;
const long am1 = (A >> 4) - one;
const long ap1_cs = FRACMUL(ap1, cs);
const long am1_cs = FRACMUL(am1, cs);
const long twosqrtalpha = 2*FRACMUL(sqrtA, alpha);
int32_t a0, a1, a2; /* these are all s6.25 format */
int32_t b0, b1, b2;
/* [0.1 .. 40] */
b0 = FRACMUL_SHL(A, ap1 - am1_cs + twosqrtalpha, 2);
/* [-16 .. 63.4] */
b1 = FRACMUL_SHL(A, am1 - ap1_cs, 3);
/* [0 .. 31.7] */
b2 = FRACMUL_SHL(A, ap1 - am1_cs - twosqrtalpha, 2);
/* [0.5 .. 10] */
a0 = ap1 + am1_cs + twosqrtalpha;
/* [-16 .. 4] */
a1 = -2*(am1 + ap1_cs);
/* [0 .. 8] */
a2 = ap1 + am1_cs - twosqrtalpha;
/* [0.1 .. 1.99] */
const long rcp_a0 = fp_div(1, a0, 55); /* s1.30 */
*c++ = FRACMUL_SHL(b0, rcp_a0, 2); /* [0.06 .. 15.9] */
*c++ = FRACMUL_SHL(b1, rcp_a0, 2); /* [-2 .. 31.7] */
*c++ = FRACMUL_SHL(b2, rcp_a0, 2); /* [0 .. 15.9] */
*c++ = FRACMUL_SHL(-a1, rcp_a0, 2); /* [-2 .. 2] */
*c++ = FRACMUL_SHL(-a2, rcp_a0, 2); /* [0 .. 1] */
}
/**
* Calculate coefficients for highshelf filter. Parameters are as for
* eq_pk_coefs, but the coefficient format is s5.26 fixed point.
*/
void eq_hs_coefs(unsigned long cutoff, unsigned long Q, long db, int32_t *c)
{
long cs;
const long one = 1 << 25; /* s6.25 */
const long sqrtA = get_replaygain_int(db*5/2) << 2; /* 10^(db/80), s5.26 */
const long A = FRACMUL_SHL(sqrtA, sqrtA, 8); /* s2.29 */
const long alpha = fp_sincos(cutoff, &cs)/(2*Q)*10 >> 1; /* s1.30 */
const long ap1 = (A >> 4) + one;
const long am1 = (A >> 4) - one;
const long ap1_cs = FRACMUL(ap1, cs);
const long am1_cs = FRACMUL(am1, cs);
const long twosqrtalpha = 2*FRACMUL(sqrtA, alpha);
int32_t a0, a1, a2; /* these are all s6.25 format */
int32_t b0, b1, b2;
/* [0.1 .. 40] */
b0 = FRACMUL_SHL(A, ap1 + am1_cs + twosqrtalpha, 2);
/* [-63.5 .. 16] */
b1 = -FRACMUL_SHL(A, am1 + ap1_cs, 3);
/* [0 .. 32] */
b2 = FRACMUL_SHL(A, ap1 + am1_cs - twosqrtalpha, 2);
/* [0.5 .. 10] */
a0 = ap1 - am1_cs + twosqrtalpha;
/* [-4 .. 16] */
a1 = 2*(am1 - ap1_cs);
/* [0 .. 8] */
a2 = ap1 - am1_cs - twosqrtalpha;
/* [0.1 .. 1.99] */
const long rcp_a0 = fp_div(1, a0, 55); /* s1.30 */
*c++ = FRACMUL_SHL(b0, rcp_a0, 2); /* [0 .. 16] */
*c++ = FRACMUL_SHL(b1, rcp_a0, 2); /* [-31.7 .. 2] */
*c++ = FRACMUL_SHL(b2, rcp_a0, 2); /* [0 .. 16] */
*c++ = FRACMUL_SHL(-a1, rcp_a0, 2); /* [-2 .. 2] */
*c++ = FRACMUL_SHL(-a2, rcp_a0, 2); /* [0 .. 1] */
}
/* We realise the filters as a second order direct form 1 structure. Direct
* form 1 was chosen because of better numerical properties for fixed point
* implementations.
*/
#if (!defined(CPU_COLDFIRE) && !defined(CPU_ARM))
void eq_filter(int32_t **x, struct eqfilter *f, unsigned num,
unsigned channels, unsigned shift)
{
unsigned c, i;
long long acc;
/* Direct form 1 filtering code.
y[n] = b0*x[i] + b1*x[i - 1] + b2*x[i - 2] + a1*y[i - 1] + a2*y[i - 2],
where y[] is output and x[] is input.
*/
for (c = 0; c < channels; c++) {
for (i = 0; i < num; i++) {
acc = (long long) x[c][i] * f->coefs[0];
acc += (long long) f->history[c][0] * f->coefs[1];
acc += (long long) f->history[c][1] * f->coefs[2];
acc += (long long) f->history[c][2] * f->coefs[3];
acc += (long long) f->history[c][3] * f->coefs[4];
f->history[c][1] = f->history[c][0];
f->history[c][0] = x[c][i];
f->history[c][3] = f->history[c][2];
x[c][i] = (acc << shift) >> 32;
f->history[c][2] = x[c][i];
}
}
}
#endif
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