# Skill: SID 6581 Sound Programming

## Use this skill when

The task involves music, sound effects, SID registers, waveforms, ADSR envelopes, filters, volume, or paddles.

## SID base

SID base: `$D400` / `54272`.

Each of the three voices uses 7 registers:

| Voice | Base decimal | Base hex |
|---|---:|---:|
| Voice 1 | 54272 | `$D400` |
| Voice 2 | 54279 | `$D407` |
| Voice 3 | 54286 | `$D40E` |

Per voice:

| Offset | Purpose |
|---:|---|
| +0 | Frequency low |
| +1 | Frequency high |
| +2 | Pulse width low |
| +3 | Pulse width high nybble |
| +4 | Control: gate, sync, ring, test, waveform |
| +5 | Attack/decay |
| +6 | Sustain/release |

Global/filter registers:

| Decimal | Hex | Purpose |
|---:|---:|---|
| 54293 | `$D415` | Filter cutoff low bits |
| 54294 | `$D416` | Filter cutoff high bits |
| 54295 | `$D417` | Resonance/filter voice routing |
| 54296 | `$D418` | Filter mode and master volume |
| 54297 | `$D419` | Paddle X / ADC 1 |
| 54298 | `$D41A` | Paddle Y / ADC 2 |
| 54299 | `$D41B` | Voice 3 oscillator output |
| 54300 | `$D41C` | Voice 3 envelope output |

## Waveform bits in control register

| Bit/mask | Meaning |
|---:|---|
| `$01` | Gate |
| `$02` | Sync |
| `$04` | Ring modulation |
| `$08` | Test |
| `$10` | Triangle |
| `$20` | Sawtooth |
| `$40` | Pulse |
| `$80` | Noise |

## Simple BASIC tone

```basic
10 S=54272
20 POKE S+24,15:REM VOLUME
30 POKE S+5,9*16+0:REM ATTACK/DECAY
40 POKE S+6,15*16+8:REM SUSTAIN/RELEASE
50 POKE S,37:POKE S+1,17:REM FREQUENCY
60 POKE S+4,17:REM TRIANGLE + GATE
70 FOR T=1 TO 500:NEXT
80 POKE S+4,16:REM GATE OFF
```

## Agent checklist

1. Initialize volume at `$D418`.
2. Set frequency before opening gate.
3. Set ADSR before gate-on.
4. Clear gate for release.
5. Avoid leaving `TEST` bit set accidentally.
6. Mention SID 6581 vs 8580 sound differences when relevant.