Sound Functions

SGB Command $08 — SOUND

Used to start/stop internal sound effect, start/stop sound using internal tone data.

 Byte  Content
 0     Command*8+Length (fixed length=1)
 1     Sound Effect A (Port 1) Decrescendo 8-bit Sound Code
 2     Sound Effect B (Port 2) Sustain     8-bit Sound Code
 3     Sound Effect Attributes
         Bit 0-1 - Sound Effect A Pitch  (0..3=Low..High)
         Bit 2-3 - Sound Effect A Volume (0..2=High..Low, 3=Mute on)
         Bit 4-5 - Sound Effect B Pitch  (0..3=Low..High)
         Bit 6-7 - Sound Effect B Volume (0..2=High..Low, 3=Not used)
 4     Music Score Code (must be zero if not used)
 5-F   Not used (zero)

See Sound Effect Tables below for a list of available pre-defined effects.

Notes:

1. Mute is only active when both bits D2 and D3 are 1.
2. When the volume is set for either Sound Effect A or Sound Effect B, mute is turned off.
3. When Mute on/off has been executed, the sound fades out/fades in.
4. Mute on/off operates on the (BGM) which is reproduced by Sound Effect A, Sound Effect B, and the Super NES APU. A “mute off” flag does not exist by itself. When mute flag is set, volume and pitch of Sound Effect A (port 1) and Sound Effect B (port 2) must be set.

SGB Command $09 — SOU_TRN

Used to transfer sound code or data to SNES Audio Processing Unit memory (APU-RAM).

 Byte  Content
 0     Command*8+Length (fixed length=1)
 1-F   Not used (zero)

The sound code/data is sent by VRAM transfer as a contiguous list of “packets”.

All 16-bit values are little-endian.

Data transfer packet format:

 0-1    Size of data below (N); if zero, this is instead a jump packet
 2-3    Destination address in S-APU RAM (typically $2B00, see below)
 4-N+3  Data to be transferred

Jump packet format:

 0-1  Must be $0000
 2-3  S-APU jump address, use $0400 to safely restart the built-in SGB BIOS' N-SPC sound engine

Possible destinations in APU-RAM are:

This function may be used to take control of the SNES sound chip, and/or to access the SNES MIDI engine. In either case it requires deeper knowledge of SNES sound programming.

SGB Sound Effect A/B Tables

Below lists the digital sound effects that are pre-defined in the SGB BIOS, and which can be used with the SGB “SOUND” Command. Effect A and B may be simultaneously used. Sound Effect A uses channels 6 and 7, Sound Effect B uses channels 0, 1, 4 and 5. Effects that use less channels will use only the upper channels (eg. 4 and 5 for a B Effect with only two channels).

Sound Effect A Flag Table

Sound effect A is used for formanto sounds (percussion sounds).

Sound Effect B Flag Table

Sound effect B is mainly used for looping sounds (sustained sounds).