mirror of
https://github.com/pumpitupdev/pumptools.git
synced 2024-12-25 20:54:50 +01:00
55 lines
3.1 KiB
Markdown
55 lines
3.1 KiB
Markdown
|
# Notes about Exceed's implementation of a sound manager
|
||
|
|
## Pre-face
|
||
|
|
To understand what the developers of AM did here, you should have some knowledge about how they had to handle sound on
|
||
|
|
the MK3 hardware which is the predecessor of the MK5 hardware that was used with Exceed. Exceed builds on the codebase
|
||
|
|
of the previous game(s), Prex 3 and Premiere 3, that ran on MK3/MK5. However, moving from Dos (MK3)/Windows XP Embedded
|
||
|
|
(MK5) to Linux (MK5), the code had to be adjusted to work on the different kind of hardware and operating system.
|
||
|
|
Their engine was targeted and optimized for the MK3 hardware platform and had to use various pieces of custom hardware
|
||
|
|
to implement stuff like: security using the lock chip, MP3 decoding and effect playback and IO.
|
||
|
|
|
||
|
|
## Sound playback, higher level view
|
||
|
|
For sound playback, the game had the following requirements:
|
||
|
|
1. For playing a song, menu background music, title screen intro music or any other music tracks, sound data encoded as
|
||
|
|
MP3 files are used. These needed to be loaded, decoded and played back whenever the game reaches certain points in the
|
||
|
|
game scene.
|
||
|
|
1. Various short sound effects, e.g. to give the user confirmation about hitting a button, have to be played back when
|
||
|
|
a certain event is triggered, e.g. user input or a scripted event in a scene. On exceed, these are stored as WAV files.
|
||
|
|
1. Audio played back by the above two items needs to be mixed because playback of both can happen simultaneously.
|
||
|
|
|
||
|
|
## MK3 hardware for decoding and audio playback
|
||
|
|
The MK3 hardware came with a dedicated piece of hardware, a [MP3 decoder and playback chip](hardware.md). Therefore,
|
||
|
|
audio data from disc was streamed encoded to the hardware for decoding and playback, and effects were triggered by
|
||
|
|
commands to the appropriate chips as their audio data is stored in a ROM chip on the board.
|
||
|
|
|
||
|
|
## Exceed's sound manager
|
||
|
|
With the move to Linux and less specialized hardware closer to a normal PC, the audio pipeline changed a lot. On Linux,
|
||
|
|
alsa/libasound is used for sending data to the underlying audio driver. Decoding of the MP3 song data is done by the
|
||
|
|
CPU. Effects are stored as WAV files and also played back using libasound.
|
||
|
|
|
||
|
|
The sound manager relies on hardware mixing using the same sound device, e.g. hw:0. This device is opened once on game
|
||
|
|
init for playing back sound effects and another time for every song/background music to be played back for the current
|
||
|
|
scene.
|
||
|
|
|
||
|
|
### Hardware sound tracks specs
|
||
|
|
#### Effect track
|
||
|
|
* Channels: 2
|
||
|
|
* Buffer size in frames: 4096
|
||
|
|
* Periods: 2
|
||
|
|
* Sample format: 16-bit signed LE
|
||
|
|
* Sample rate: 44100
|
||
|
|
* Sample order: FL, FR
|
||
|
|
|
||
|
|
#### Song track
|
||
|
|
* Channels: 2
|
||
|
|
* Buffer size in frames: 16384
|
||
|
|
* Periods: 8
|
||
|
|
* Sample format: 16-bit signed LE
|
||
|
|
* Sample rate: 44100
|
||
|
|
* Sample order: FL, FR
|
||
|
|
|
||
|
|
### Issues on todays distros
|
||
|
|
However, this way of mixing is not supported anymore by alsa. Instead, you have to use software mixing using dmix which
|
||
|
|
is supported by alsa's built in plugin system today. But, that doesn't seem to work properly with different
|
||
|
|
configurations from different versions of alsa on today's available distros.
|
||
|
|
|
||
|
|
Fortunately, this got fixed already on Exceed 2 which implements its own software mixer in the pump engine.
|