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|
/*----------------------------------------------------------------------------
//
// 3 Band EQ :)
//
// EQ.C - Main Source file for 3 band EQ
//
// (c) Neil C / Etanza Systems / 2K6
//
// Shouts / Loves / Moans = etanza at lycos dot co dot uk
//
// This work is hereby placed in the public domain for all purposes, including
// use in commercial applications.
//
// The author assumes NO RESPONSIBILITY for any problems caused by the use of
// this software.
//
//----------------------------------------------------------------------------*/
/* NOTES :
//
// - Original filter code by Paul Kellet (musicdsp.pdf)
//
// - Uses 4 first order filters in series, should give 24dB per octave
//
// - Now with P4 Denormal fix :)
//----------------------------------------------------------------------------*/
/* ----------
//| Includes |
// ----------*/
#include <stdio.h>
#include <string.h>
#include <math.h>
#include "eq.h"
#include "macros.h"
/* -----------
//| Constants |
// -----------*/
static double vsa = (1.0 / 4294967295.0); /* Very small amount (Denormal Fix) */
/* ---------------
//| Initialise EQ |
// ---------------*/
/* Recommended frequencies are ...
//
// lowfreq = 880 Hz
// highfreq = 5000 Hz
//
// Set mixfreq to whatever rate your system is using (eg 48Khz)*/
void init_3band_state(EQSTATE * es, int lowfreq, int highfreq, int mixfreq)
{
/* Clear state */
memset(es, 0, sizeof(EQSTATE));
/* Set Low/Mid/High gains to unity */
es->lg = 1.0;
es->mg = 1.0;
es->hg = 1.0;
/* Calculate filter cutoff frequencies */
es->lf = 2 * sin(M_PI * ((double) lowfreq / (double) mixfreq));
es->hf = 2 * sin(M_PI * ((double) highfreq / (double) mixfreq));
}
/* ---------------
//| EQ one sample |
// ---------------*/
/* - sample can be any range you like :)
//
// Note that the output will depend on the gain settings for each band
// (especially the bass) so may require clipping before output, but you
// knew that anyway :)*/
double do_3band(EQSTATE * es, int sample)
{
/* Locals */
double l, m, h; /* Low / Mid / High - Sample Values */
/* Filter #1 (lowpass) */
es->f1p0 += (es->lf * ((double) sample - es->f1p0)) + vsa;
es->f1p1 += (es->lf * (es->f1p0 - es->f1p1));
es->f1p2 += (es->lf * (es->f1p1 - es->f1p2));
es->f1p3 += (es->lf * (es->f1p2 - es->f1p3));
l = es->f1p3;
/* Filter #2 (highpass) */
es->f2p0 += (es->hf * ((double) sample - es->f2p0)) + vsa;
es->f2p1 += (es->hf * (es->f2p0 - es->f2p1));
es->f2p2 += (es->hf * (es->f2p1 - es->f2p2));
es->f2p3 += (es->hf * (es->f2p2 - es->f2p3));
h = es->sdm3 - es->f2p3;
/* Calculate midrange (signal - (low + high)) */
/* m = es->sdm3 - (h + l); */
/* fix from http://www.musicdsp.org/showArchiveComment.php?ArchiveID=236 ? */
m = sample - (h + l);
/* Scale, Combine and store */
l *= es->lg;
m *= es->mg;
h *= es->hg;
/* Shuffle history buffer */
es->sdm3 = es->sdm2;
es->sdm2 = es->sdm1;
es->sdm1 = sample;
/* Return result */
return (int) (l + m + h);
}
|
