How to do it?

MUSIC FILE FORMAT v1.0

• Header (16 bytes):
  • +0: [2] Magic: “SD” ($53 $44)
  • +2: [1] Version (1)
  • +3: [1] Flags
  • +4: [2] Tempo (ms per row)
  • +6: [1] Number of instruments
  • +7: [1] Number of patterns
  • +8: [1] Song length (orders)
  • +9: [7] Reserved

• Instrument Table (10 bytes each):
  • +0: [1] Instrument ID
  • +1: [1] Instrument Type
• Waveforms:
  • +2: [1] Waveform (WAVE_xx constant)
  • +3: [1] Pulse width / duty cycle
  • +4: [1] Attack
  • +5: [1] Decay
  • +6: [1] Sustain
  • +7: [1] Release
  • +8: [1] Default volume
  • +9: [1] Reserved
• Samples:
  • +2: [1] address (bank)
  • +3: [1] address (low byte)
  • +4: [1] address (high byte)
  • +5: [1] Volume
  • +6: [1] Playback speed
  • +7: [1] reserved
  • +8: [1] reserved
  • +9: [1] reserved

NOTE: need to do more research on what data we should include with samples. How does SNES/etc. do it?

• Order List (1 byte each):
  • Pattern numbers in playback order
  • Terminated by $FF ($FFFF or $0000?)

• Patterns:
  • Each pattern is a sequence of rows
  • Each row is a sequence of channel commands
  • Row terminated by $00
  • Pattern terminated by $FF (see above)

Command Byte:

• Bits 7-6: Channel (0-3)
• Bits 5-4: Command type
• Bits 3-0: Depends on command type

OR

• Command Byte
• Channel Byte
• Data Word + Data Word + Data Word (Reserved)

Command Types:

• 00 = Note On (3 bytes total)
  • [Cmd] [Note] [Instrument]
• 01 = Note Off (1 byte)
  • [Cmd]
• 10 = Set Volume (2 bytes)
  • [Cmd] [Volume]
• 11 = Effect (3 bytes)
  • [Cmd] [Effect Type] [Effect Param]

• $00 = Rest (no change)
• $01-$60 = Notes (C0 to B7)
• $61 = Note off
• $FF = End of pattern

• Note calculation:
  • Note = (Octave * 12) + Semitone + 1
  • C4 = (4 * 12) + 0 + 1 = 49 = $31
  • A4 = (4 * 12) + 9 + 1 = 58 = $3A

• on a row: CWND CWND CWND CWND
• “Channel, Waveform, Note, Duration” ex 12G4Q is channel 1, waveform 2, note G4, quarter note
• Can have commands like TEMPO = 90