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/* Copyright (C) 2003, 2004, 2005, 2006, 2008, 2009 Dean Beeler, Jerome Fisher
* Copyright (C) 2011 Dean Beeler, Jerome Fisher, Sergey V. Mikayev
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation, either version 2.1 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
//#include <cmath>
//#include <cstring>
#include "mt32emu.h"
#include "DelayReverb.h"
using namespace MT32Emu;
// CONFIRMED: The values below are found via analysis of digital samples. Checked with all time and level combinations.
// Obviously:
// rightDelay = (leftDelay - 2) * 2 + 2
// echoDelay = rightDelay - 1
// Leaving these separate in case it's useful for work on other reverb modes...
const Bit32u REVERB_TIMINGS[8][3]= {
// {leftDelay, rightDelay, feedbackDelay}
{402, 802, 801},
{626, 1250, 1249},
{962, 1922, 1921},
{1490, 2978, 2977},
{2258, 4514, 4513},
{3474, 6946, 6945},
{5282, 10562, 10561},
{8002, 16002, 16001}
};
const float REVERB_FADE[8] = {0.0f, -0.049400051f, -0.08220577f, -0.131861118f, -0.197344907f, -0.262956344f, -0.345162114f, -0.509508615f};
const float REVERB_FEEDBACK67 = -0.629960524947437f; // = -EXP2F(-2 / 3)
const float REVERB_FEEDBACK = -0.682034520443118f; // = -EXP2F(-53 / 96)
const float LPF_VALUE = 0.594603558f; // = EXP2F(-0.75f)
DelayReverb::DelayReverb() {
buf = NULL;
sampleRate = 0;
setParameters(0, 0);
}
DelayReverb::~DelayReverb() {
delete[] buf;
}
void DelayReverb::open(unsigned int newSampleRate) {
if (newSampleRate != sampleRate || buf == NULL) {
sampleRate = newSampleRate;
delete[] buf;
// If we ever need a speedup, set bufSize to EXP2F(ceil(log2(bufSize))) and use & instead of % to find buf indexes
bufSize = 16384 * sampleRate / 32000;
buf = new float[bufSize];
recalcParameters();
// mute buffer
bufIx = 0;
if (buf != NULL) {
for (unsigned int i = 0; i < bufSize; i++) {
buf[i] = 0.0f;
}
}
}
// FIXME: IIR filter value depends on sample rate as well
}
void DelayReverb::close() {
delete[] buf;
buf = NULL;
}
// This method will always trigger a flush of the buffer
void DelayReverb::setParameters(Bit8u newTime, Bit8u newLevel) {
time = newTime;
level = newLevel;
recalcParameters();
}
void DelayReverb::recalcParameters() {
// Number of samples between impulse and eventual appearance on the left channel
delayLeft = REVERB_TIMINGS[time][0] * sampleRate / 32000;
// Number of samples between impulse and eventual appearance on the right channel
delayRight = REVERB_TIMINGS[time][1] * sampleRate / 32000;
// Number of samples between a response and that response feeding back/echoing
delayFeedback = REVERB_TIMINGS[time][2] * sampleRate / 32000;
if (time < 6) {
feedback = REVERB_FEEDBACK;
} else {
feedback = REVERB_FEEDBACK67;
}
// Fading speed, i.e. amplitude ratio of neighbor responses
fade = REVERB_FADE[level];
}
void DelayReverb::process(const float *inLeft, const float *inRight, float *outLeft, float *outRight, unsigned long numSamples) {
if (buf == NULL) {
return;
}
for (unsigned int sampleIx = 0; sampleIx < numSamples; sampleIx++) {
// The ring buffer write index moves backwards; reads are all done with positive offsets.
Bit32u bufIxPrev = (bufIx + 1) % bufSize;
Bit32u bufIxLeft = (bufIx + delayLeft) % bufSize;
Bit32u bufIxRight = (bufIx + delayRight) % bufSize;
Bit32u bufIxFeedback = (bufIx + delayFeedback) % bufSize;
// Attenuated input samples and feedback response are directly added to the current ring buffer location
float sample = fade * (inLeft[sampleIx] + inRight[sampleIx]) + feedback * buf[bufIxFeedback];
// Single-pole IIR filter found on real devices
buf[bufIx] = buf[bufIxPrev] + (sample - buf[bufIxPrev]) * LPF_VALUE;
outLeft[sampleIx] = buf[bufIxLeft];
outRight[sampleIx] = buf[bufIxRight];
bufIx = (bufSize + bufIx - 1) % bufSize;
}
}
bool DelayReverb::isActive() const {
// Quick hack: Return true iff all samples in the left buffer are the same and
// all samples in the right buffers are the same (within the sample output threshold).
if (buf == NULL) {
return false;
}
float last = buf[0] * 8192.0f;
for (unsigned int i = 1; i < bufSize; i++) {
float s = (buf[i] * 8192.0f);
if (fabs(s - last) > 1.0f) {
return true;
}
}
return false;
}
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