= Appendix 5 Sound System
This is Appendix 5 of the [[SD-8516 Programmer's Reference Guide]].

The SD-8516 is paired with the SD-450 sound subsystem; named for featuring 4 independent voices with 5 waveforms available, each with a programmable ADSR envelope.

== Voice Architecture
Each voice occupies 16 bytes of memory in Bank 1:

|= Offset |= Register |= Description |
| +$00 | FREQ_LO | Frequency low byte |
| +$01 | FREQ_HI | Frequency high byte |
| +$02 | GATE | Waveform/gate control |
| +$03 | VOLUME | Volume (0-255) |
| +$04 | ATTACK | Attack time |
| +$05 | DECAY | Decay time |
| +$06 | SUSTAIN | Sustain level |
| +$07 | RELEASE | Release time |
| +$08 | DATA1 | Pulse width / noise type |
| +$09-$0F | Reserved | Future expansion |

**Voice base addresses:**
* Voice 0: {{{$1EF80}}}
* Voice 1: {{{$1EF90}}}
* Voice 2: {{{$1EFA0}}}
* Voice 3: {{{$1EFB0}}}

== Waveforms
Gate register values:
* 0: Silent (gate off)
* 1: Square wave
* 2: Triangle wave
* 3: Sawtooth wave
* 4: Sine wave
* 5: Pulse wave (variable width via DATA1)
* 6: White/pink/brown noise (type via DATA1)

== ADSR Envelope
The Attack-Decay-Sustain-Release envelope shapes each note:
* **Attack:** Time to reach peak volume (0-255 × 10ms)
* **Decay:** Time to decay to sustain level (0-255 × 10ms)
* **Sustain:** Held volume level (0.0-1.0 of peak)
* **Release:** Time to fade to silence after gate off (0-255 × 10ms)

**Example:**
<codify armasm>
; Play middle C on voice 0
    LDA $112B           ; C4 frequency (262 Hz / 0.0596)
    STA [$1ED00]         ; FREQ_LO/HI
    LDAL $01            ; Square wave
    STAL [$1ED02]        ; GATE
    LDAL $4D            ; ~30% volume
    STAL [$1ED03]        ; VOLUME
</codify>


== Sound System Memory Map
Also see [[Appendix 3 Memory Map]].

=== Sound System ($01EF80–$01EFBF) – 64 bytes total

^ Address Range ^ Size ^ Symbol / Register ^ Description ^
| $01EF80–$01EF8F | 16 bytes | SOUND0_BASE | **Voice 0** |
| $01EF80 | 1 byte | SOUND0_FREQ_LO | Frequency low byte (bits 7–0) |
| $01EF81 | 1 byte | SOUND0_FREQ_HI | Frequency high byte (bits 15–8) |
| $01EF82 | 1 byte | SOUND0_GATE | Gate / Waveform select (gate bit + waveform type: noise, pulse, saw, triangle, etc.) |
| $01EF83 | 1 byte | SOUND0_VOLUME | Master volume for voice 0 (usually 0–15, may include global volume in some implementations)|
| $01EF84 | 1 byte | SOUND0_ATTACK | Attack rate (0–15) |
| $01EF85 | 1 byte | SOUND0_DECAY | Decay rate (0–15) |
| $01EF86 | 1 byte | SOUND0_SUSTAIN | Sustain level (0–15) |
| $01EF87 | 1 byte | SOUND0_RELEASE | Release rate (0–15) |
| $01EF88 | 1 byte | SOUND0_DATA1 | Voice-specific control / extra parameter 1 (e.g. pulse width low, filter routing, etc.) |
| $01EF89 | 1 byte | SOUND0_DATA2 | Voice-specific control / extra parameter 2 (e.g. pulse width high, ring/mod flags, etc.) |
| $01EF8A–$01EF8F | 6 bytes | — | **Reserved / unused / future expansion** for Voice 0 |

^ Address Range ^ Size ^ Symbol / Register ^ Description ^
| $01EF90–$01EF9F | 16 bytes | SOUND1_BASE | **Voice 1** |
| $01EF90 | 1 byte | SOUND1_FREQ_LO | Frequency low byte |
| $01EF91 | 1 byte | SOUND1_FREQ_HI | Frequency high byte |
| $01EF92 | 1 byte | SOUND1_GATE | Gate / Waveform select |
| $01EF93 | 1 byte | SOUND1_VOLUME | Volume for voice 1 |
| $01EF94 | 1 byte | SOUND1_ATTACK | Attack rate |
| $01EF95 | 1 byte | SOUND1_DECAY | Decay rate |
| $01EF96 | 1 byte | SOUND1_SUSTAIN | Sustain level |
| $01EF97 | 1 byte | SOUND1_RELEASE | Release rate |
| $01EF98 | 1 byte | SOUND1_DATA1 | Extra control 1 |
| $01EF99 | 1 byte | SOUND1_DATA2 | Extra control 2 |
| $01EF9A–$01EF9F | 6 bytes | — | **Reserved / unused / future expansion** for Voice 1 |

^ Address Range ^ Size ^ Symbol / Register ^ Description ^
| $01EFA0–$01EFAF | 16 bytes | SOUND2_BASE | **Voice 2** |
| $01EFA0 | 1 byte | SOUND2_FREQ_LO | Frequency low byte |
| $01EFA1 | 1 byte | SOUND2_FREQ_HI | Frequency high byte |
| $01EFA2 | 1 byte | SOUND2_GATE | Gate / Waveform select |
| $01EFA3 | 1 byte | SOUND2_VOLUME | Volume for voice 2 |
| $01EFA4 | 1 byte | SOUND2_ATTACK | Attack rate |
| $01EFA5 | 1 byte | SOUND2_DECAY | Decay rate |
| $01EFA6 | 1 byte | SOUND2_SUSTAIN | Sustain level |
| $01EFA7 | 1 byte | SOUND2_RELEASE | Release rate |
| $01EFA8 | 1 byte | SOUND2_DATA1 | Extra control 1 |
| $01EFA9 | 1 byte | SOUND2_DATA2 | Extra control 2 |
| $01EFAA–$01EFAF | 6 bytes | — | **Reserved / unused / future expansion** for Voice 2 |

^ Address Range ^ Size ^ Symbol / Register ^ Description ^
| $01EFB0–$01EFBF | 16 bytes | SOUND3_BASE | **Voice 3** |
| $01EFB0 | 1 byte | SOUND3_FREQ_LO | Frequency low byte |
| $01EFB1 | 1 byte | SOUND3_FREQ_HI | Frequency high byte |
| $01EFB2 | 1 byte | SOUND3_GATE | Gate / Waveform select |
| $01EFB3 | 1 byte | SOUND3_VOLUME | Volume for voice 3 |
| $01EFB4 | 1 byte | SOUND3_ATTACK | Attack rate |
| $01EFB5 | 1 byte | SOUND3_DECAY | Decay rate |
| $01EFB6 | 1 byte | SOUND3_SUSTAIN | Sustain level |
| $01EFB7 | 1 byte | SOUND3_RELEASE | Release rate |
| $01EFB8 | 1 byte | SOUND3_DATA1 | Extra control 1 |
| $01EFB9 | 1 byte | SOUND3_DATA2 | Extra control 2 |
| $01EFBA–$01EFBF | 6 bytes | — | **Reserved / unused / future expansion** for Voice 3 |