Audio & Music Tutorial

This tutorial covers SNES audio including the SPC700 sound chip, BRR samples, and SNESMOD tracker playback.

SNES Audio Architecture

The SNES has a dedicated SPC700 sound processor with:

• 8 audio channels
• 64KB dedicated audio RAM
• BRR (Bit Rate Reduction) sample compression
• Hardware ADSR envelopes
• Echo/reverb effects

Audio Options in OpenSNES

Method	Best For	Size	Complexity
Legacy Audio	Simple SFX, tones	~500 bytes	Low
SNESMOD	Music + SFX	~5.5KB	Medium

SNESMOD (Recommended)

SNESMOD is a tracker-based audio engine supporting Impulse Tracker (.it) modules.

Setup

1. Create music in a tracker (OpenMPT recommended)
2. Export as Impulse Tracker (.it) format
3. Convert with smconv tool
4. Link soundbank with your ROM

Makefile Configuration

# Enable SNESMOD
USE_SNESMOD    := 1
USE_LIB        := 1
LIB_MODULES    := console sprite input
 
# Soundbank source files
SOUNDBANK_SRC  := music/mymusic.it sfx/effects.it

Basic Music Playback

#include <snes.h>
#include <snes/snesmod.h>
#include "soundbank.h"
 
int main(void) {
    consoleInit();
 
    // Initialize SNESMOD (uploads SPC driver)
    snesmodInit();
 
    // Set soundbank location
    snesmodSetSoundbank(SOUNDBANK_BANK);
 
    // Load a module (defined in soundbank.h)
    snesmodLoadModule(MOD_MYMUSIC);
 
    // Start playback
    snesmodPlay(0);  // 0 = start from beginning
 
    setScreenOn();
 
    while (1) {
        WaitForVBlank();
 
        // MUST call every frame!
        snesmodProcess();
    }
    return 0;
}

Sound Effects

#include <snes/snesmod.h>
#include "soundbank.h"
 
// Load effects at startup
void init_audio(void) {
    snesmodInit();
    snesmodSetSoundbank(SOUNDBANK_BANK);
 
    // Load sound effects (indices from soundbank.h)
    snesmodLoadEffect(0);  // Jump sound
    snesmodLoadEffect(1);  // Coin sound
    snesmodLoadEffect(2);  // Hit sound
}
 
// Play effect when needed
void play_jump_sound(void) {
    // snesmodPlayEffect(effectId, volume, pan, pitch)
    snesmodPlayEffect(0, 127, 128, SNESMOD_PITCH_NORMAL);
    // volume: 0-127
    // pan: 0=left, 128=center, 255=right
    // pitch: SNESMOD_PITCH_LOW/NORMAL/HIGH (4/8/12)
}
 
void play_coin_sound(void) {
    // Higher pitch for coins
    snesmodPlayEffect(1, 100, 128, SNESMOD_PITCH_HIGH);
}

Volume Control

// Set master volume (0-127)
snesmodSetModuleVolume(127);
 
// Fade out over time
snesmodFadeVolume(0, 4);  // target=0, speed=4
 
// Pause/Resume
snesmodPause();
snesmodResume();
 
// Stop completely
snesmodStop();

Creating Music with OpenMPT

1. Download OpenMPT (free)
2. Create new Impulse Tracker module
3. Keep within SNES limits:
   • Max 8 channels
   • Total samples < 58KB
   • 32kHz max sample rate
4. Export as .it file

smconv Tool

# Convert music for soundbank
smconv -s -o soundbank -b 1 music.it effects.it
 
# Output files:
# - soundbank.asm  (link with ROM)
# - soundbank.h    (module/effect IDs)
# - soundbank.bnk  (binary data)

Pitch Constants

#define SNESMOD_PITCH_LOW    4   // 16kHz - lower pitch
#define SNESMOD_PITCH_NORMAL 8   // 32kHz - normal pitch
#define SNESMOD_PITCH_HIGH   12  // 48kHz - higher pitch

Important: Call snesmodProcess()!

You MUST call snesmodProcess() every frame! Failure to do so causes:

• Audio glitches and stuttering
• Command buffer overflow
• Desynchronization

while (1) {
    WaitForVBlank();
    snesmodProcess();  // CRITICAL!
 
    // ... game logic
}

Example: Music + SFX

#include <snes.h>
#include <snes/snesmod.h>
#include "soundbank.h"
 
int main(void) {
    u16 pad, pad_prev = 0, pad_pressed;
 
    consoleInit();
 
    // Initialize audio
    snesmodInit();
    snesmodSetSoundbank(SOUNDBANK_BANK);
 
    // Load music module
    snesmodLoadModule(MOD_LEVEL1);
 
    // Load sound effects
    snesmodLoadEffect(0);  // Jump
    snesmodLoadEffect(1);  // Coin
 
    // Start music
    snesmodPlay(0);
 
    setScreenOn();
 
    while (1) {
        WaitForVBlank();
        snesmodProcess();
 
        // Read input
        while (REG_HVBJOY & 0x01) {}
        u16 pad = REG_JOY1L | (REG_JOY1H << 8);
        pad_pressed = pad & ~pad_prev;
        pad_prev = pad;
        if (pad == 0xFFFF) pad_pressed = 0;
 
        // Play SFX on button press
        if (pad_pressed & KEY_A) {
            snesmodPlayEffect(0, 127, 128, SNESMOD_PITCH_NORMAL);
        }
        if (pad_pressed & KEY_B) {
            snesmodPlayEffect(1, 127, 128, SNESMOD_PITCH_HIGH);
        }
    }
    return 0;
}

Memory Usage

Component	Size
SPC700 Driver	~5.5KB
Sample Data	Up to ~58KB
Echo Buffer	~4KB (at $D000-$FFFF)

Total audio RAM: 64KB

Tips

1. Keep samples small - Use lower sample rates for less important sounds
2. Reuse samples - Same sample at different pitches for variety
3. Test on hardware - Emulator timing may differ
4. Use echo sparingly - Takes 4KB+ of audio RAM

Examples

• examples/audio/snesmod_music/ - Music playback demo
• examples/audio/snesmod_sfx/ - Sound effects demo

Next Steps

• SNESMOD API Reference
• Back to Graphics