diff options
Diffstat (limited to 'audio/softsynth/mt32/Tables.cpp')
| -rw-r--r-- | audio/softsynth/mt32/Tables.cpp | 33 |
1 files changed, 17 insertions, 16 deletions
diff --git a/audio/softsynth/mt32/Tables.cpp b/audio/softsynth/mt32/Tables.cpp index 5353a74079..743820b1f8 100644 --- a/audio/softsynth/mt32/Tables.cpp +++ b/audio/softsynth/mt32/Tables.cpp @@ -1,5 +1,5 @@ /* Copyright (C) 2003, 2004, 2005, 2006, 2008, 2009 Dean Beeler, Jerome Fisher - * Copyright (C) 2011 Dean Beeler, Jerome Fisher, Sergey V. Mikayev + * 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 @@ -72,24 +72,25 @@ Tables::Tables() { //synth->printDebug("%d: %d", i, pulseWidth100To255[i]); } - // The LA32 chip presumably has such a table inside as the internal computaions seem to be performed using fixed point math with 12-bit fractions - for (int i = 0; i < 4096; i++) { - exp2[i] = EXP2F(i / 4096.0f); + // The LA32 chip contains an exponent table inside. The table contains 12-bit integer values. + // The actual table size is 512 rows. The 9 higher bits of the fractional part of the argument are used as a lookup address. + // To improve the precision of computations, the lower bits are supposed to be used for interpolation as the LA32 chip also + // contains another 512-row table with inverted differences between the main table values. + for (int i = 0; i < 512; i++) { + exp9[i] = Bit16u(8191.5f - EXP2F(13.0f + ~i / 512.0f)); } - // found from sample analysis - resAmpFadeFactor[7] = 1.0f / 8.0f; - resAmpFadeFactor[6] = 2.0f / 8.0f; - resAmpFadeFactor[5] = 3.0f / 8.0f; - resAmpFadeFactor[4] = 5.0f / 8.0f; - resAmpFadeFactor[3] = 8.0f / 8.0f; - resAmpFadeFactor[2] = 12.0f / 8.0f; - resAmpFadeFactor[1] = 16.0f / 8.0f; - resAmpFadeFactor[0] = 31.0f / 8.0f; - - for (int i = 0; i < 5120; i++) { - sinf10[i] = sin(FLOAT_PI * i / 2048.0f); + // There is a logarithmic sine table inside the LA32 chip. The table contains 13-bit integer values. + for (int i = 1; i < 512; i++) { + logsin9[i] = Bit16u(0.5f - LOG2F(sin((i + 0.5f) / 1024.0f * FLOAT_PI)) * 1024.0f); } + + // The very first value is clamped to the maximum possible 13-bit integer + logsin9[0] = 8191; + + // found from sample analysis + static const Bit8u resAmpDecayFactorTable[] = {31, 16, 12, 8, 5, 3, 2, 1}; + resAmpDecayFactor = resAmpDecayFactorTable; } } |