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