src/mt32/DelayReverb.cpp

/* Copyright (C) 2003, 2004, 2005, 2006, 2008, 2009 Dean Beeler, Jerome Fisher
 * Copyright (C) 2011, 2012, 2013 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"
#include "FileStream.h"

namespace MT32Emu {

// CONFIRMED: The values below are found via analysis of digital samples and tracing reverb RAM address / data lines. 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...
static 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}
};

// Reverb amp is found as dryAmp * wetAmp
static const Bit32u REVERB_AMP[8] = {0x20*0x18, 0x50*0x18, 0x50*0x28, 0x50*0x40, 0x50*0x60, 0x50*0x80, 0x50*0xA8, 0x50*0xF8};
static const Bit32u REVERB_FEEDBACK67 = 0x60;
static const Bit32u REVERB_FEEDBACK = 0x68;
static const float LPF_VALUE = 0x68 / 256.0f;

static const Bit32u BUFFER_SIZE = 16384;

DelayReverb::DelayReverb() {
        buf = NULL;
    bufIx = 0;
    delayLeft = 0;
    delayRight = 0;
    delayFeedback = 0;
    amp = 0;
    feedback = 0;
        setParameters(0, 0);


        // loadstate init
        //bufSize = 0;
}

DelayReverb::~DelayReverb() {
        delete[] buf;
}

void DelayReverb::open() {
        if (buf == NULL) {
                delete[] buf;

                buf = new float[BUFFER_SIZE];

                recalcParameters();

                // mute buffer
                bufIx = 0;
                if (buf != NULL) {
                        for (unsigned int i = 0; i < BUFFER_SIZE; i++) {
                                buf[i] = 0.0f;
                        }
                }
        }
}

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];
        // Number of samples between impulse and eventual appearance on the right channel
        delayRight = REVERB_TIMINGS[time][1];
        // Number of samples between a response and that response feeding back/echoing
        delayFeedback = REVERB_TIMINGS[time][2];

        if (level < 3 || time < 6) {
                feedback = REVERB_FEEDBACK / 256.0f;
        } else {
                feedback = REVERB_FEEDBACK67 / 256.0f;
        }

        // Overall output amp
        amp = (level == 0 && time == 0) ? 0.0f : REVERB_AMP[level] / 65536.0f;
}

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) % BUFFER_SIZE;
                Bit32u bufIxLeft = (bufIx + delayLeft) % BUFFER_SIZE;
                Bit32u bufIxRight = (bufIx + delayRight) % BUFFER_SIZE;
                Bit32u bufIxFeedback = (bufIx + delayFeedback) % BUFFER_SIZE;

                // Attenuated input samples and feedback response are directly added to the current ring buffer location
                float lpfIn = amp * (inLeft[sampleIx] + inRight[sampleIx]) + feedback * buf[bufIxFeedback];

                // Single-pole IIR filter found on real devices
                buf[bufIx] = buf[bufIxPrev] * LPF_VALUE - lpfIn;

                outLeft[sampleIx] = buf[bufIxLeft];
                outRight[sampleIx] = buf[bufIxRight];

                bufIx = (BUFFER_SIZE + bufIx - 1) % BUFFER_SIZE;
        }
}

bool DelayReverb::isActive() const {
        if (buf == NULL) return false;

        float *b = buf;
        float max = 0.001f;
        for (Bit32u i = 0; i < BUFFER_SIZE; i++) {
                if ((*b < -max) || (*b > max)) return true;
                b++;
        }
        return false;
}


void DelayReverb::saveState( std::ostream &stream )
{
        stream.write(reinterpret_cast<const char*>(&time), sizeof(time) );
        stream.write(reinterpret_cast<const char*>(&level), sizeof(level) );
        //stream.write(reinterpret_cast<const char*>(&sampleRate), sizeof(sampleRate) );
        //stream.write(reinterpret_cast<const char*>(&bufSize), sizeof(bufSize) );
        stream.write(reinterpret_cast<const char*>(&bufIx), sizeof(bufIx) );

        if( buf )
                stream.write(reinterpret_cast<const char*>(buf), sizeof(buf) * sizeof(float) );

        stream.write(reinterpret_cast<const char*>(&delayLeft), sizeof(delayLeft) );
        stream.write(reinterpret_cast<const char*>(&delayRight), sizeof(delayRight) );
        stream.write(reinterpret_cast<const char*>(&delayFeedback), sizeof(delayFeedback) );
        //stream.write(reinterpret_cast<const char*>(&fade), sizeof(fade) );
        stream.write(reinterpret_cast<const char*>(&feedback), sizeof(feedback) );
}


void DelayReverb::loadState( std::istream &stream )
{
        stream.read(reinterpret_cast<char*>(&time), sizeof(time) );
        stream.read(reinterpret_cast<char*>(&level), sizeof(level) );
        //stream.read(reinterpret_cast<char*>(&sampleRate), sizeof(sampleRate) );
        //stream.read(reinterpret_cast<char*>(&bufSize), sizeof(bufSize) );
        stream.read(reinterpret_cast<char*>(&bufIx), sizeof(bufIx) );


        if( buf ) delete[] buf;
        if( sizeof(buf) == 0 ) {
                buf = NULL;
        }
        else {
                buf = new float[ sizeof(buf) ];
                stream.read(reinterpret_cast<char*>(buf), sizeof(buf) * sizeof(float) );
        }


        stream.read(reinterpret_cast<char*>(&delayLeft), sizeof(delayLeft) );
        stream.read(reinterpret_cast<char*>(&delayRight), sizeof(delayRight) );
        stream.read(reinterpret_cast<char*>(&delayFeedback), sizeof(delayFeedback) );
        //stream.read(reinterpret_cast<char*>(&fade), sizeof(fade) );
        stream.read(reinterpret_cast<char*>(&feedback), sizeof(feedback) );
}

}