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:

• ADSR
• GAIN

ADSR Envelope Timings

See: S-SMP ADSR

Name	Address	Bits	Notes
ADSR (1)	$X5	EDDD AAAA	ADSR enable (E), decay rate (D), attack rate (A).
ADSR (2)	$X6	SSSR RRRR	Sustain level (S), release rate (R).

At a rate according to the 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]: envelope -= 1, then envelope -= envelope >> 8.
• Release at period[R]: envelope -= 1, then envelope -= envelope >> 8.

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.

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

ADSR Decay D Time (ms) 0 1200 1 740 2 440 3 290 4 180 5 110 6 74 7 37

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

Name	Address	Bits	Notes
GAIN	$X7	0VVV VVVV 1MMV VVVV	Mode (M), value (V).

At a rate according to the 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: envelope -= 1, then: envelope -= envelope >> 8.

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

GAIN
Decrease Linear		Decrease Exponential		Increase Linear		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 period table. Each entry is how many S-SMP clocks elapse per envelope operation.

DSP Period Table
Infinite	2048	1536	1280	1024	768	640	512	384	320	256	192	160	128	96	80
64	48	40	32	24	20	16	12	10	8	6	5	4	3	2	1