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