Sound Functions

SGB Command $08 — SOUND

Used to start/stop internal sound effect, start/stop sound usinginternal 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-definedeffects.

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 SoundEffect A, Sound Effect B, and the Super NES APU. A “mute off” flagdoes not exist by itself. When mute flag is set, volume and pitch ofSound 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 byVRAM 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/orto access the SNES MIDI engine. In either case it requires deeperknowledge of SNES sound programming.

SGB Sound Effect A/B Tables

Below lists the digital sound effects that are pre-defined in theSGB 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 channels0, 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).