View source for DSP envelopes

The envelope value ('''ENVX''') of each [[S-SMP]] DSP voice is driven by either an ADSR envelope, or a gain control. This gives an additional way to automatically shape the volume of the voice over time, aside from its '''VOL''' registers.

The ADSR describes a 4 stage envelope:
* '''Attack''' begins at key-on, rising from 0 to full over a chosen amount of time.
* '''Decay''' lowers from full to a chosen sustain level.
* '''Sustain''' is the volume level reached after the decay concludes.
* '''Release''' begins at key-off, lowering to 0 with an exponential decay.

Internally the envelope is an 11-bit value multiplied by by the voice output. The '''ENVX''' value that can be read from the DSP contains only the high 7 bits.

See:
* [[S-SMP#ADSR|ADSR]]
* [[S-SMP#GAIN|GAIN]]

== ADSR Envelope Timings ==

See: [[S-SMP#ADSR|S-SMP ADSR]]

{| class="wikitable"
! Name
! Address
! Bits
! Notes
|-
! ADSR (1)
! $X5
| style="text-align: right" | <tt style="white-space: nowrap">EDDD AAAA</tt>
| ADSR enable (E), decay rate (D), attack rate (A).
|-
! ADSR (2)
! $X6
| style="text-align: right" | <tt style="white-space: nowrap">SSSR RRRR</tt>
| Sustain level (S), release rate (R).
|}

At a rate according to the [[#Period Table|period table]] the following action is performed, and the envelope is clamped to 0-2047 ($7FF):
* Attack at period[A*2+1]: adds 32, or if A=$F adds 1024 ($400).
* Decay at period[D*2+16]: <tt>envelope -= 1</tt>, then <tt>envelope -= envelope >> 8</tt>.
* Release at period[R]: <tt>envelope -= 1</tt>, then <tt>envelope -= envelope >> 8</tt>.

Table timings:
* Attack is the time from 0 to full.
* Decay is the time from full to sustain level.
* Release is the time from full to 0.

{|
| style="vertical-align: top" |

{| class="wikitable"
! colspan=2 | ADSR Attack
|-
! A !! Time (ms)
|-
| $0 || 4100
|-
| $1 || 2600
|-
| $2 || 1500
|-
| $3 || 1000
|-
| $4 || 640
|-
| $5 || 380
|-
| $6 || 260
|-
| $7 || 160
|-
| $8 || 96
|-
| $9 || 64
|-
| $A || 40
|-
| $B || 24
|-
| $C || 16
|-
| $D || 10
|-
| $E || 6
|-
| $F || 0
|}

| style="vertical-align: top" |

{| class="wikitable"
! colspan=2 | ADSR Decay
|-
! D !! Time (ms)
|-
| 0 || 1200
|-
| 1 || 740
|-
| 2 || 440
|-
| 3 || 290
|-
| 4 || 180
|-
| 5 || 110
|-
| 6 || 74
|-
| 7 || 37
|}

| style="vertical-align: top" |

{| class="wikitable"
! colspan=4 | ADSR Release
|-
! R !! Time (ms) !! R !! Time (ms)
|-
| $00 || Infinite || $10 || 1200
|-
| $01 || 38000    || $11 || 880
|-
| $02 || 28000    || $12 || 740
|-
| $03 || 24000    || $13 || 590
|-
| $04 || 19000    || $14 || 440
|-
| $05 || 14000    || $15 || 370
|-
| $06 || 12000    || $16 || 290
|-
| $07 || 9400     || $17 || 220
|-
| $08 || 7100     || $18 || 180
|-
| $09 || 5900     || $19 || 150
|-
| $0A || 4700     || $1A || 110
|-
| $0B || 3500     || $1B || 92
|-
| $0C || 2900     || $1C || 74
|-
| $0D || 2400     || $1D || 55
|-
| $0E || 1800     || $1E || 37
|-
| $0F || 1500     || $1F || 18
|}

|}

== Gain Timings ==

See: [[S-SMP#GAIN|S-SMP GAIN]]

{| class="wikitable"
! Name
! Address
! Bits
! Notes
|-
! GAIN
! $X7
| style="text-align: right" | <tt style="white-space: nowrap">0VVV VVVV</tt><br/> <tt style="white-space: nowrap">1MMV VVVV</tt>
| Mode (M), value (V).
|}

At a rate according to the [[#Period Table|period table]] the following action is performed, and the envelope is clamped to 0-2047 ($7FF):
* Linear gain adds or subtracts 32.
* Bent gain adds 32 if below 1536 ($600), or 8 if above.
* Exponential is two steps: <tt>envelope -= 1</tt>, then: <tt>envelope -= envelope >> 8</tt>.

This table gives times taken between 0 volume and full volume (or the reverse).

{| class="wikitable"
! colspan=8 | GAIN
|-
! colspan=2 | Decrease Linear !! colspan=2 | Decrease Exponential !! colspan=2 | Increase Linear !! colspan=2 | Increase Bent
|-
! V !! Time (ms) !! V !! Time (ms) !! V !! Time (ms) !! V !! Time (ms)
|-
! $80
| Infinite
! $A0
| Infinite
! $C0
| Infinite
! $E0
| Infinite
|-
! $81
| 4100
! $A1
| 38000
! $C1
| 4100
! $E1
| 7200
|-
! $82
| 3100
! $A2
| 28000
! $C2
| 3100
! $E2
| 5400
|-
|-
! $83
| 2600
! $A3
| 24000
! $C3
| 2600
! $E3
| 4600
|-
! $84
| 2000
! $A4
| 19000
! $C4
| 2000
! $E4
| 3500
|-
! $85
| 1500
! $A5
| 14000
! $C5
| 1500
! $E5
| 2600
|-
! $86
| 1300
! $A6
| 12000
! $C6
| 1300
! $E6
| 2300
|-
! $87
| 1000
! $A7
| 9400
! $C7
| 1000
! $E7
| 1800
|-
! $88
| 770
! $A8
| 7100
! $C8
| 770
! $E8
| 1300
|-
! $89
| 640
! $A9
| 5900
! $C9
| 640
! $E9
| 1100
|-
! $8A
| 510
! $AA
| 4700
! $CA
| 510
! $EA
| 900
|-
! $8B
| 380
! $AB
| 3500
! $CB
| 380
! $EB
| 670
|-
! $8C
| 320
! $AC
| 2900
! $CC
| 320
! $EC
| 560
|-
! $8D
| 260
! $AD
| 2400
! $CD
| 260
! $ED
| 450
|-
! $8E
| 190
! $AE
| 1800
! $CE
| 190
! $EE
| 340
|-
! $8F
| 160
! $AF
| 1500
! $CF
| 160
! $EF
| 280
|-
! $90
| 130
! $B0
| 1200
! $D0
| 130
! $F0
| 220
|-
! $91
| 96
! $B1
| 880
! $D1
| 96
! $F1
| 170
|-
! $92
| 80
! $B2
| 740
! $D2
| 80
! $F2
| 140
|-
! $93
| 64
! $B3
| 590
! $D3
| 64
! $F3
| 110
|-
! $94
| 48
! $B4
| 440
! $D4
| 48
! $F4
| 84
|-
! $95
| 40
! $B5
| 370
! $D5
| 40
! $F5
| 70
|-
! $96
| 32
! $B6
| 290
! $D6
| 32
! $F6
| 56
|-
! $97
| 24
! $B7
| 220
! $D7
| 24
! $F7
| 42
|-
! $98
| 20
! $B8
| 180
! $D8
| 20
! $F8
| 35
|-
! $99
| 16
! $B9
| 150
! $D9
| 16
! $F9
| 28
|-
! $9A
| 12
! $BA
| 110
! $DA
| 12
! $FA
| 21
|-
! $9B
| 10
! $BB
| 92
! $DB
| 10
! $FB
| 18
|-
! $9C
| 8
! $BC
| 74
! $DC
| 8
! $FC
| 14
|-
! $9D
| 6
! $DD
| 55
! $BD
| 6
! $FD
| 11
|-
! $9E
| 4
! $BE
| 37
! $DE
| 4
! $FE
| 7
|-
! $9F
| 2
! $BF
| 18
! $DF
| 2
! $FF
| 3.5
|}

== Period Table ==

The rate of DSP envelope events are controlled by a common table of 32 periods. Each entry is how many S-SMP clocks elapse per envelope operation. The table is arranged in groups of 3.

Additionally, each column of periods appears to have a delay offset applied to it, affecting when the operation occurs. If <tt>counter</tt> is the number of S-SMP clocks elapsed, the envelope operation is applied when the following is true:
* <tt>0 == (counter + offset[rate]) % period[rate]</tt>

{|
| style="vertical-align: top" |

{| class="wikitable"
! colspan=16 | DSP Period Table
|-
! / !! +0 !! +1 !! +2
|-
! 0
| Infinite || 2048 || 1536
|-
! 3
| 1280 || 1024 || 768
|-
! 6
| 640  || 512  || 384
|-
! 9
| 320  || 256  || 192
|-
! 12
| 160  || 128  || 96
|-
! 15
| 80   || 64   || 48
|-
! 18
| 40   || 32   || 24
|-
! 21
| 20   || 16   || 12
|-
! 24
| 10   || 8    || 6
|-
! 27
| 5    || 4    || 3
|-
! 30
| 2    || 1    || -
|}

| style="vertical-align: top" |

{| class="wikitable"
! colspan=16 | DSP Period Table
|-
! / !! +0 !! +1 !! +2
|-
! 0
| Never || 0 || 1040
|-
! 3
| 536 || 0 || 1040
|-
! 6
| 536 || 0 || 1040
|-
! 9
| 536 || 0 || 1040
|-
! 12
| 536 || 0 || 1040
|-
! 15
| 536 || 0 || 1040
|-
! 18
| 536 || 0 || 1040
|-
! 21
| 536 || 0 || 1040
|-
! 24
| 536 || 0 || 1040
|-
! 27
| 536 || 0 || 1040
|-
! 30
| 536 || 0 || -
|}

|}

[[Category:Sound]]