mirror of
https://github.com/ekeeke/Genesis-Plus-GX.git
synced 2024-12-30 21:21:49 +01:00
133 lines
3.2 KiB
C
133 lines
3.2 KiB
C
/*----------------------------------------------------------------------------
|
|
//
|
|
// 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 "types.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);
|
|
}
|