diff options
| author |  Alexey Yakovenko <wakeroid@gmail.com> | 2010-06-22 22:26:45 +0200 |
|---|---|---|
| committer | Alexey Yakovenko <wakeroid@gmail.com> | 2010-06-22 22:26:45 +0200 |
| commit | 20575a338e9640eca924958484a5fee800e09971 (patch) | |
| tree | efaeac41a8a21bea1c90494b3b0968169d4f8732 /plugins/ao/eng_psf/peops2/adsr2.c | |
| parent | c901a7cbf52ee234220f21b85c2e77667264d16c (diff) | |
audio overload plugin - highly experimental; no seeking; crashes
Diffstat (limited to 'plugins/ao/eng_psf/peops2/adsr2.c')
| -rw-r--r-- | plugins/ao/eng_psf/peops2/adsr2.c | 656 |
1 files changed, 656 insertions, 0 deletions
diff --git a/plugins/ao/eng_psf/peops2/adsr2.c b/plugins/ao/eng_psf/peops2/adsr2.c new file mode 100644 index 00000000..442cc38f --- /dev/null +++ b/plugins/ao/eng_psf/peops2/adsr2.c @@ -0,0 +1,656 @@ +/***************************************************************************
+ adsr.c - description
+ -------------------
+ begin : Wed May 15 2002
+ copyright : (C) 2002 by Pete Bernert
+ email : BlackDove@addcom.de
+ ***************************************************************************/
+
+/***************************************************************************
+ * *
+ * This program is free software; you can redistribute it and/or modify *
+ * it under the terms of the GNU General Public License as published by *
+ * the Free Software Foundation; either version 2 of the License, or *
+ * (at your option) any later version. See also the license.txt file for *
+ * additional informations. *
+ * *
+ ***************************************************************************/
+
+//*************************************************************************//
+// History of changes:
+//
+// 2003/05/14 - xodnizel
+// - removed stopping of reverb on sample end
+//
+// 2003/01/06 - Pete
+// - added Neill's ADSR timings
+//
+// 2002/05/15 - Pete
+// - generic cleanup for the Peops release
+//
+//*************************************************************************//
+
+#include "stdafx.h"
+
+#define _IN_ADSR
+
+// will be included from spu.c
+#ifdef _IN_SPU
+
+////////////////////////////////////////////////////////////////////////
+// ADSR func
+////////////////////////////////////////////////////////////////////////
+
+unsigned long RateTable[160];
+
+void InitADSR(void) // INIT ADSR
+{
+ unsigned long r,rs,rd;int i;
+
+ memset(RateTable,0,sizeof(unsigned long)*160); // build the rate table according to Neill's rules (see at bottom of file)
+
+ r=3;rs=1;rd=0;
+
+ for(i=32;i<160;i++) // we start at pos 32 with the real values... everything before is 0
+ {
+ if(r<0x3FFFFFFF)
+ {
+ r+=rs;
+ rd++;if(rd==5) {rd=1;rs*=2;}
+ }
+ if(r>0x3FFFFFFF) r=0x3FFFFFFF;
+
+ RateTable[i]=r;
+ }
+}
+
+////////////////////////////////////////////////////////////////////////
+
+INLINE void StartADSR(int ch) // MIX ADSR
+{
+ s_chan[ch].ADSRX.lVolume=1; // and init some adsr vars
+ s_chan[ch].ADSRX.State=0;
+ s_chan[ch].ADSRX.EnvelopeVol=0;
+}
+
+////////////////////////////////////////////////////////////////////////
+
+INLINE int MixADSR(int ch) // MIX ADSR
+{
+ if(s_chan[ch].bStop) // should be stopped:
+ { // do release
+ if(s_chan[ch].ADSRX.ReleaseModeExp)
+ {
+ switch((s_chan[ch].ADSRX.EnvelopeVol>>28)&0x7)
+ {
+ case 0: s_chan[ch].ADSRX.EnvelopeVol-=RateTable[(4*(s_chan[ch].ADSRX.ReleaseRate^0x1F))-0x18 +0 + 32]; break;
+ case 1: s_chan[ch].ADSRX.EnvelopeVol-=RateTable[(4*(s_chan[ch].ADSRX.ReleaseRate^0x1F))-0x18 +4 + 32]; break;
+ case 2: s_chan[ch].ADSRX.EnvelopeVol-=RateTable[(4*(s_chan[ch].ADSRX.ReleaseRate^0x1F))-0x18 +6 + 32]; break;
+ case 3: s_chan[ch].ADSRX.EnvelopeVol-=RateTable[(4*(s_chan[ch].ADSRX.ReleaseRate^0x1F))-0x18 +8 + 32]; break;
+ case 4: s_chan[ch].ADSRX.EnvelopeVol-=RateTable[(4*(s_chan[ch].ADSRX.ReleaseRate^0x1F))-0x18 +9 + 32]; break;
+ case 5: s_chan[ch].ADSRX.EnvelopeVol-=RateTable[(4*(s_chan[ch].ADSRX.ReleaseRate^0x1F))-0x18 +10+ 32]; break;
+ case 6: s_chan[ch].ADSRX.EnvelopeVol-=RateTable[(4*(s_chan[ch].ADSRX.ReleaseRate^0x1F))-0x18 +11+ 32]; break;
+ case 7: s_chan[ch].ADSRX.EnvelopeVol-=RateTable[(4*(s_chan[ch].ADSRX.ReleaseRate^0x1F))-0x18 +12+ 32]; break;
+ }
+ }
+ else
+ {
+ s_chan[ch].ADSRX.EnvelopeVol-=RateTable[(4*(s_chan[ch].ADSRX.ReleaseRate^0x1F))-0x0C + 32];
+ }
+
+ if(s_chan[ch].ADSRX.EnvelopeVol<0)
+ {
+ s_chan[ch].ADSRX.EnvelopeVol=0;
+ s_chan[ch].bOn=0;
+ //s_chan[ch].bReverb=0;
+ //s_chan[ch].bNoise=0;
+ }
+
+ s_chan[ch].ADSRX.lVolume=s_chan[ch].ADSRX.EnvelopeVol>>21;
+ return s_chan[ch].ADSRX.lVolume;
+ }
+ else // not stopped yet?
+ {
+ if(s_chan[ch].ADSRX.State==0) // -> attack
+ {
+ if(s_chan[ch].ADSRX.AttackModeExp)
+ {
+ if(s_chan[ch].ADSRX.EnvelopeVol<0x60000000)
+ s_chan[ch].ADSRX.EnvelopeVol+=RateTable[(s_chan[ch].ADSRX.AttackRate^0x7F)-0x10 + 32];
+ else
+ s_chan[ch].ADSRX.EnvelopeVol+=RateTable[(s_chan[ch].ADSRX.AttackRate^0x7F)-0x18 + 32];
+ }
+ else
+ {
+ s_chan[ch].ADSRX.EnvelopeVol+=RateTable[(s_chan[ch].ADSRX.AttackRate^0x7F)-0x10 + 32];
+ }
+
+ if(s_chan[ch].ADSRX.EnvelopeVol<0)
+ {
+ s_chan[ch].ADSRX.EnvelopeVol=0x7FFFFFFF;
+ s_chan[ch].ADSRX.State=1;
+ }
+
+ s_chan[ch].ADSRX.lVolume=s_chan[ch].ADSRX.EnvelopeVol>>21;
+ return s_chan[ch].ADSRX.lVolume;
+ }
+ //--------------------------------------------------//
+ if(s_chan[ch].ADSRX.State==1) // -> decay
+ {
+ switch((s_chan[ch].ADSRX.EnvelopeVol>>28)&0x7)
+ {
+ case 0: s_chan[ch].ADSRX.EnvelopeVol-=RateTable[(4*(s_chan[ch].ADSRX.DecayRate^0x1F))-0x18+0 + 32]; break;
+ case 1: s_chan[ch].ADSRX.EnvelopeVol-=RateTable[(4*(s_chan[ch].ADSRX.DecayRate^0x1F))-0x18+4 + 32]; break;
+ case 2: s_chan[ch].ADSRX.EnvelopeVol-=RateTable[(4*(s_chan[ch].ADSRX.DecayRate^0x1F))-0x18+6 + 32]; break;
+ case 3: s_chan[ch].ADSRX.EnvelopeVol-=RateTable[(4*(s_chan[ch].ADSRX.DecayRate^0x1F))-0x18+8 + 32]; break;
+ case 4: s_chan[ch].ADSRX.EnvelopeVol-=RateTable[(4*(s_chan[ch].ADSRX.DecayRate^0x1F))-0x18+9 + 32]; break;
+ case 5: s_chan[ch].ADSRX.EnvelopeVol-=RateTable[(4*(s_chan[ch].ADSRX.DecayRate^0x1F))-0x18+10+ 32]; break;
+ case 6: s_chan[ch].ADSRX.EnvelopeVol-=RateTable[(4*(s_chan[ch].ADSRX.DecayRate^0x1F))-0x18+11+ 32]; break;
+ case 7: s_chan[ch].ADSRX.EnvelopeVol-=RateTable[(4*(s_chan[ch].ADSRX.DecayRate^0x1F))-0x18+12+ 32]; break;
+ }
+
+ if(s_chan[ch].ADSRX.EnvelopeVol<0) s_chan[ch].ADSRX.EnvelopeVol=0;
+ if(((s_chan[ch].ADSRX.EnvelopeVol>>27)&0xF) <= s_chan[ch].ADSRX.SustainLevel)
+ {
+ s_chan[ch].ADSRX.State=2;
+ }
+
+ s_chan[ch].ADSRX.lVolume=s_chan[ch].ADSRX.EnvelopeVol>>21;
+ return s_chan[ch].ADSRX.lVolume;
+ }
+ //--------------------------------------------------//
+ if(s_chan[ch].ADSRX.State==2) // -> sustain
+ {
+ if(s_chan[ch].ADSRX.SustainIncrease)
+ {
+ if(s_chan[ch].ADSRX.SustainModeExp)
+ {
+ if(s_chan[ch].ADSRX.EnvelopeVol<0x60000000)
+ s_chan[ch].ADSRX.EnvelopeVol+=RateTable[(s_chan[ch].ADSRX.SustainRate^0x7F)-0x10 + 32];
+ else
+ s_chan[ch].ADSRX.EnvelopeVol+=RateTable[(s_chan[ch].ADSRX.SustainRate^0x7F)-0x18 + 32];
+ }
+ else
+ {
+ s_chan[ch].ADSRX.EnvelopeVol+=RateTable[(s_chan[ch].ADSRX.SustainRate^0x7F)-0x10 + 32];
+ }
+
+ if(s_chan[ch].ADSRX.EnvelopeVol<0)
+ {
+ s_chan[ch].ADSRX.EnvelopeVol=0x7FFFFFFF;
+ }
+ }
+ else
+ {
+ if(s_chan[ch].ADSRX.SustainModeExp)
+ {
+ switch((s_chan[ch].ADSRX.EnvelopeVol>>28)&0x7)
+ {
+ case 0: s_chan[ch].ADSRX.EnvelopeVol-=RateTable[((s_chan[ch].ADSRX.SustainRate^0x7F))-0x1B +0 + 32];break;
+ case 1: s_chan[ch].ADSRX.EnvelopeVol-=RateTable[((s_chan[ch].ADSRX.SustainRate^0x7F))-0x1B +4 + 32];break;
+ case 2: s_chan[ch].ADSRX.EnvelopeVol-=RateTable[((s_chan[ch].ADSRX.SustainRate^0x7F))-0x1B +6 + 32];break;
+ case 3: s_chan[ch].ADSRX.EnvelopeVol-=RateTable[((s_chan[ch].ADSRX.SustainRate^0x7F))-0x1B +8 + 32];break;
+ case 4: s_chan[ch].ADSRX.EnvelopeVol-=RateTable[((s_chan[ch].ADSRX.SustainRate^0x7F))-0x1B +9 + 32];break;
+ case 5: s_chan[ch].ADSRX.EnvelopeVol-=RateTable[((s_chan[ch].ADSRX.SustainRate^0x7F))-0x1B +10+ 32];break;
+ case 6: s_chan[ch].ADSRX.EnvelopeVol-=RateTable[((s_chan[ch].ADSRX.SustainRate^0x7F))-0x1B +11+ 32];break;
+ case 7: s_chan[ch].ADSRX.EnvelopeVol-=RateTable[((s_chan[ch].ADSRX.SustainRate^0x7F))-0x1B +12+ 32];break;
+ }
+ }
+ else
+ {
+ s_chan[ch].ADSRX.EnvelopeVol-=RateTable[((s_chan[ch].ADSRX.SustainRate^0x7F))-0x0F + 32];
+ }
+
+ if(s_chan[ch].ADSRX.EnvelopeVol<0)
+ {
+ s_chan[ch].ADSRX.EnvelopeVol=0;
+ }
+ }
+ s_chan[ch].ADSRX.lVolume=s_chan[ch].ADSRX.EnvelopeVol>>21;
+ return s_chan[ch].ADSRX.lVolume;
+ }
+ }
+ return 0;
+}
+
+#endif
+
+/*
+James Higgs ADSR investigations:
+
+PSX SPU Envelope Timings
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+First, here is an extract from doomed's SPU doc, which explains the basics
+of the SPU "volume envelope":
+
+*** doomed doc extract start ***
+
+--------------------------------------------------------------------------
+Voices.
+--------------------------------------------------------------------------
+The SPU has 24 hardware voices. These voices can be used to reproduce sample
+data, noise or can be used as frequency modulator on the next voice.
+Each voice has it's own programmable ADSR envelope filter. The main volume
+can be programmed independently for left and right output.
+
+The ADSR envelope filter works as follows:
+Ar = Attack rate, which specifies the speed at which the volume increases
+ from zero to it's maximum value, as soon as the note on is given. The
+ slope can be set to lineair or exponential.
+Dr = Decay rate specifies the speed at which the volume decreases to the
+ sustain level. Decay is always decreasing exponentially.
+Sl = Sustain level, base level from which sustain starts.
+Sr = Sustain rate is the rate at which the volume of the sustained note
+ increases or decreases. This can be either lineair or exponential.
+Rr = Release rate is the rate at which the volume of the note decreases
+ as soon as the note off is given.
+
+ lvl |
+ ^ | /\Dr __
+ Sl _| _ / _ \__--- \
+ | / ---__ \ Rr
+ | /Ar Sr \ \
+ | / \\
+ |/___________________\________
+ ->time
+
+The overal volume can also be set to sweep up or down lineairly or
+exponentially from it's current value. This can be done seperately
+for left and right.
+
+Relevant SPU registers:
+-------------------------------------------------------------
+$1f801xx8 Attack/Decay/Sustain level
+bit |0f|0e 0d 0c 0b 0a 09 08|07 06 05 04|03 02 01 00|
+desc.|Am| Ar |Dr |Sl |
+
+Am 0 Attack mode Linear
+ 1 Exponential
+
+Ar 0-7f attack rate
+Dr 0-f decay rate
+Sl 0-f sustain level
+-------------------------------------------------------------
+$1f801xxa Sustain rate, Release Rate.
+bit |0f|0e|0d|0c 0b 0a 09 08 07 06|05|04 03 02 01 00|
+desc.|Sm|Sd| 0| Sr |Rm|Rr |
+
+Sm 0 sustain rate mode linear
+ 1 exponential
+Sd 0 sustain rate mode increase
+ 1 decrease
+Sr 0-7f Sustain Rate
+Rm 0 Linear decrease
+ 1 Exponential decrease
+Rr 0-1f Release Rate
+
+Note: decay mode is always Expontial decrease, and thus cannot
+be set.
+-------------------------------------------------------------
+$1f801xxc Current ADSR volume
+bit |0f 0e 0d 0c 0b 0a 09 08 07 06 05 04 03 02 01 00|
+desc.|ADSRvol |
+
+ADSRvol Returns the current envelope volume when
+ read.
+-- James' Note: return range: 0 -> 32767
+
+*** doomed doc extract end ***
+
+By using a small PSX proggie to visualise the envelope as it was played,
+the following results for envelope timing were obtained:
+
+1. Attack rate value (linear mode)
+
+ Attack value range: 0 -> 127
+
+ Value | 48 | 52 | 56 | 60 | 64 | 68 | 72 | | 80 |
+ -----------------------------------------------------------------
+ Frames | 11 | 21 | 42 | 84 | 169| 338| 676| |2890|
+
+ Note: frames is no. of PAL frames to reach full volume (100%
+ amplitude)
+
+ Hmm, noticing that the time taken to reach full volume doubles
+ every time we add 4 to our attack value, we know the equation is
+ of form:
+ frames = k * 2 ^ (value / 4)
+
+ (You may ponder about envelope generator hardware at this point,
+ or maybe not... :)
+
+ By substituting some stuff and running some checks, we get:
+
+ k = 0.00257 (close enuf)
+
+ therefore,
+ frames = 0.00257 * 2 ^ (value / 4)
+ If you just happen to be writing an emulator, then you can probably
+ use an equation like:
+
+ %volume_increase_per_tick = 1 / frames
+
+
+ ------------------------------------
+ Pete:
+ ms=((1<<(value>>2))*514)/10000
+ ------------------------------------
+
+2. Decay rate value (only has log mode)
+
+ Decay value range: 0 -> 15
+
+ Value | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 |
+ ------------------------------------------------
+ frames | | | | | 6 | 12 | 24 | 47 |
+
+ Note: frames here is no. of PAL frames to decay to 50% volume.
+
+ formula: frames = k * 2 ^ (value)
+
+ Substituting, we get: k = 0.00146
+
+ Further info on logarithmic nature:
+ frames to decay to sustain level 3 = 3 * frames to decay to
+ sustain level 9
+
+ Also no. of frames to 25% volume = roughly 1.85 * no. of frames to
+ 50% volume.
+
+ Frag it - just use linear approx.
+
+ ------------------------------------
+ Pete:
+ ms=((1<<value)*292)/10000
+ ------------------------------------
+
+
+3. Sustain rate value (linear mode)
+
+ Sustain rate range: 0 -> 127
+
+ Value | 48 | 52 | 56 | 60 | 64 | 68 | 72 |
+ -------------------------------------------
+ frames | 9 | 19 | 37 | 74 | 147| 293| 587|
+
+ Here, frames = no. of PAL frames for volume amplitude to go from 100%
+ to 0% (or vice-versa).
+
+ Same formula as for attack value, just a different value for k:
+
+ k = 0.00225
+
+ ie: frames = 0.00225 * 2 ^ (value / 4)
+
+ For emulation purposes:
+
+ %volume_increase_or_decrease_per_tick = 1 / frames
+
+ ------------------------------------
+ Pete:
+ ms=((1<<(value>>2))*450)/10000
+ ------------------------------------
+
+
+4. Release rate (linear mode)
+
+ Release rate range: 0 -> 31
+
+ Value | 13 | 14 | 15 | 16 | 17 |
+ ---------------------------------------------------------------
+ frames | 18 | 36 | 73 | 146| 292|
+
+ Here, frames = no. of PAL frames to decay from 100% vol to 0% vol
+ after "note-off" is triggered.
+
+ Formula: frames = k * 2 ^ (value)
+
+ And so: k = 0.00223
+
+ ------------------------------------
+ Pete:
+ ms=((1<<value)*446)/10000
+ ------------------------------------
+
+
+Other notes:
+
+Log stuff not figured out. You may get some clues from the "Decay rate"
+stuff above. For emu purposes it may not be important - use linear
+approx.
+
+To get timings in millisecs, multiply frames by 20.
+
+
+
+- James Higgs 17/6/2000
+james7780@yahoo.com
+
+//---------------------------------------------------------------
+
+OLD adsr mixing according to james' rules... has to be called
+every one millisecond
+
+
+ long v,v2,lT,l1,l2,l3;
+
+ if(s_chan[ch].bStop) // psx wants to stop? -> release phase
+ {
+ if(s_chan[ch].ADSR.ReleaseVal!=0) // -> release not 0: do release (if 0: stop right now)
+ {
+ if(!s_chan[ch].ADSR.ReleaseVol) // --> release just started? set up the release stuff
+ {
+ s_chan[ch].ADSR.ReleaseStartTime=s_chan[ch].ADSR.lTime;
+ s_chan[ch].ADSR.ReleaseVol=s_chan[ch].ADSR.lVolume;
+ s_chan[ch].ADSR.ReleaseTime = // --> calc how long does it take to reach the wanted sus level
+ (s_chan[ch].ADSR.ReleaseTime*
+ s_chan[ch].ADSR.ReleaseVol)/1024;
+ }
+ // -> NO release exp mode used (yet)
+ v=s_chan[ch].ADSR.ReleaseVol; // -> get last volume
+ lT=s_chan[ch].ADSR.lTime- // -> how much time is past?
+ s_chan[ch].ADSR.ReleaseStartTime;
+ l1=s_chan[ch].ADSR.ReleaseTime;
+
+ if(lT<l1) // -> we still have to release
+ {
+ v=v-((v*lT)/l1); // --> calc new volume
+ }
+ else // -> release is over: now really stop that sample
+ {v=0;s_chan[ch].bOn=0;s_chan[ch].ADSR.ReleaseVol=0;s_chan[ch].bNoise=0;}
+ }
+ else // -> release IS 0: release at once
+ {
+ v=0;s_chan[ch].bOn=0;s_chan[ch].ADSR.ReleaseVol=0;s_chan[ch].bNoise=0;
+ }
+ }
+ else
+ {//--------------------------------------------------// not in release phase:
+ v=1024;
+ lT=s_chan[ch].ADSR.lTime;
+ l1=s_chan[ch].ADSR.AttackTime;
+
+ if(lT<l1) // attack
+ { // no exp mode used (yet)
+// if(s_chan[ch].ADSR.AttackModeExp)
+// {
+// v=(v*lT)/l1;
+// }
+// else
+ {
+ v=(v*lT)/l1;
+ }
+ if(v==0) v=1;
+ }
+ else // decay
+ { // should be exp, but who cares? ;)
+ l2=s_chan[ch].ADSR.DecayTime;
+ v2=s_chan[ch].ADSR.SustainLevel;
+
+ lT-=l1;
+ if(lT<l2)
+ {
+ v-=(((v-v2)*lT)/l2);
+ }
+ else // sustain
+ { // no exp mode used (yet)
+ l3=s_chan[ch].ADSR.SustainTime;
+ lT-=l2;
+ if(s_chan[ch].ADSR.SustainModeDec>0)
+ {
+ if(l3!=0) v2+=((v-v2)*lT)/l3;
+ else v2=v;
+ }
+ else
+ {
+ if(l3!=0) v2-=(v2*lT)/l3;
+ else v2=v;
+ }
+
+ if(v2>v) v2=v;
+ if(v2<=0) {v2=0;s_chan[ch].bOn=0;s_chan[ch].ADSR.ReleaseVol=0;s_chan[ch].bNoise=0;}
+
+ v=v2;
+ }
+ }
+ }
+
+ //----------------------------------------------------//
+ // ok, done for this channel, so increase time
+
+ s_chan[ch].ADSR.lTime+=1; // 1 = 1.020408f ms;
+
+ if(v>1024) v=1024; // adjust volume
+ if(v<0) v=0;
+ s_chan[ch].ADSR.lVolume=v; // store act volume
+
+ return v; // return the volume factor
+*/
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+
+/*
+-----------------------------------------------------------------------------
+Neill Corlett
+Playstation SPU envelope timing notes
+-----------------------------------------------------------------------------
+
+This is preliminary. This may be wrong. But the model described herein fits
+all of my experimental data, and it's just simple enough to sound right.
+
+ADSR envelope level ranges from 0x00000000 to 0x7FFFFFFF internally.
+The value returned by channel reg 0xC is (envelope_level>>16).
+
+Each sample, an increment or decrement value will be added to or
+subtracted from this envelope level.
+
+Create the rate log table. The values double every 4 entries.
+ entry #0 = 4
+
+ 4, 5, 6, 7,
+ 8,10,12,14,
+ 16,20,24,28, ...
+
+ entry #40 = 4096...
+ entry #44 = 8192...
+ entry #48 = 16384...
+ entry #52 = 32768...
+ entry #56 = 65536...
+
+increments and decrements are in terms of ratelogtable[n]
+n may exceed the table bounds (plan on n being between -32 and 127).
+table values are all clipped between 0x00000000 and 0x3FFFFFFF
+
+when you "voice on", the envelope is always fully reset.
+(yes, it may click. the real thing does this too.)
+
+envelope level begins at zero.
+
+each state happens for at least 1 cycle
+(transitions are not instantaneous)
+this may result in some oddness: if the decay rate is uberfast, it will cut
+the envelope from full down to half in one sample, potentially skipping over
+the sustain level
+
+ATTACK
+------
+- if the envelope level has overflowed past the max, clip to 0x7FFFFFFF and
+ proceed to DECAY.
+
+Linear attack mode:
+- line extends upward to 0x7FFFFFFF
+- increment per sample is ratelogtable[(Ar^0x7F)-0x10]
+
+Logarithmic attack mode:
+if envelope_level < 0x60000000:
+ - line extends upward to 0x60000000
+ - increment per sample is ratelogtable[(Ar^0x7F)-0x10]
+else:
+ - line extends upward to 0x7FFFFFFF
+ - increment per sample is ratelogtable[(Ar^0x7F)-0x18]
+
+DECAY
+-----
+- if ((envelope_level>>27)&0xF) <= Sl, proceed to SUSTAIN.
+ Do not clip to the sustain level.
+- current line ends at (envelope_level & 0x07FFFFFF)
+- decrement per sample depends on (envelope_level>>28)&0x7
+ 0: ratelogtable[(4*(Dr^0x1F))-0x18+0]
+ 1: ratelogtable[(4*(Dr^0x1F))-0x18+4]
+ 2: ratelogtable[(4*(Dr^0x1F))-0x18+6]
+ 3: ratelogtable[(4*(Dr^0x1F))-0x18+8]
+ 4: ratelogtable[(4*(Dr^0x1F))-0x18+9]
+ 5: ratelogtable[(4*(Dr^0x1F))-0x18+10]
+ 6: ratelogtable[(4*(Dr^0x1F))-0x18+11]
+ 7: ratelogtable[(4*(Dr^0x1F))-0x18+12]
+ (note that this is the same as the release rate formula, except that
+ decay rates 10-1F aren't possible... those would be slower in theory)
+
+SUSTAIN
+-------
+- no terminating condition except for voice off
+- Sd=0 (increase) behavior is identical to ATTACK for both log and linear.
+- Sd=1 (decrease) behavior:
+Linear sustain decrease:
+- line extends to 0x00000000
+- decrement per sample is ratelogtable[(Sr^0x7F)-0x0F]
+Logarithmic sustain decrease:
+- current line ends at (envelope_level & 0x07FFFFFF)
+- decrement per sample depends on (envelope_level>>28)&0x7
+ 0: ratelogtable[(Sr^0x7F)-0x1B+0]
+ 1: ratelogtable[(Sr^0x7F)-0x1B+4]
+ 2: ratelogtable[(Sr^0x7F)-0x1B+6]
+ 3: ratelogtable[(Sr^0x7F)-0x1B+8]
+ 4: ratelogtable[(Sr^0x7F)-0x1B+9]
+ 5: ratelogtable[(Sr^0x7F)-0x1B+10]
+ 6: ratelogtable[(Sr^0x7F)-0x1B+11]
+ 7: ratelogtable[(Sr^0x7F)-0x1B+12]
+
+RELEASE
+-------
+- if the envelope level has overflowed to negative, clip to 0 and QUIT.
+
+Linear release mode:
+- line extends to 0x00000000
+- decrement per sample is ratelogtable[(4*(Rr^0x1F))-0x0C]
+
+Logarithmic release mode:
+- line extends to (envelope_level & 0x0FFFFFFF)
+- decrement per sample depends on (envelope_level>>28)&0x7
+ 0: ratelogtable[(4*(Rr^0x1F))-0x18+0]
+ 1: ratelogtable[(4*(Rr^0x1F))-0x18+4]
+ 2: ratelogtable[(4*(Rr^0x1F))-0x18+6]
+ 3: ratelogtable[(4*(Rr^0x1F))-0x18+8]
+ 4: ratelogtable[(4*(Rr^0x1F))-0x18+9]
+ 5: ratelogtable[(4*(Rr^0x1F))-0x18+10]
+ 6: ratelogtable[(4*(Rr^0x1F))-0x18+11]
+ 7: ratelogtable[(4*(Rr^0x1F))-0x18+12]
+
+-----------------------------------------------------------------------------
+*/
+
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