1 files changed, 150 insertions, 0 deletions
diff --git a/audio/softsynth/mt32/DelayReverb.cpp b/audio/softsynth/mt32/DelayReverb.cpp
new file mode 100644
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+++ b/audio/softsynth/mt32/DelayReverb.cpp
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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;
+}