Implementing the Game Boy's Audio Processing Unit (APU) is one of the most challenging parts when developing a Game Boy emulator. Particularly, because debugging is hard and you may not want to create an exact replica, but something that simulates fast and sounds good enough. The Game Boy Noise Test supports you in this process, allowing you to test features of the noise channel and evaluate their acoustical impressions.
Open noise_test.gb with your Game Boy emulator.
After the boot, you arrive at the following user interface:
It allows you to modify all noise-channel-related settings:
| Name | Address | Bits | Function |
|---|---|---|---|
| NR41 | 0xFF20 | --LL LLLL |
Length load |
| NR42 | 0xFF21 | VVVV APPP |
Starting volume, envelope add mode, period |
| NR43 | 0xFF22 | SSSS WDDD |
Clock shift, width mode of LFSR, divisor code |
| NR44 | 0xFF23 | TL-- ---- |
Trigger, length enable |
Values can be changed by selecting them and pressing left or right on the D-pad. Once content with the configuration, move the cursor to "PLAY" and press A. By pressing SELECT you can also switch between the following predefined settings:
| Preset | Description | Golden Reference |
|---|---|---|
| 0 | Empty preset | - |
| 1 | Hi-hat from Tetris | |
| 2 | Snare from Tetris | |
| 3 | Fading in wave from The Legend Of Zelda: Link's Awakening | |
| 4 | Fading out wave from The Legend Of Zelda: Link's Awakening | |
| 5 | Fading in snare | |
| 6 | Bombshell Koopa (Nokobon) explosion from Super Mario Land | |
| 7 | Explosion | |
| 8 | Chiptune-like Explosion | |
| 9 | First noise part of defeating a Fighter Fly from Super Mario Land |
In the table are also golden reference audio samples that were recorded from the original DMG-01 Game Boy.
Note: As of yet Github Markdown does not support the HTML audio element. See readme_assets to get the golden reference samples.
In src/noise_test.asm you find the source code of the Game Boy Noise Test.
Assuming RBGDS is installed, it can be built with a simple make.