Audio

This section is in beta. See the note on the cheat sheet.

Like most PS2 peripherals, the sound chip (SPU2) is IOP-side hardware. There is no direct path from the EE to SPU2. Every audio package in this SDK is either an IOP driver that accesses SPU2 registers or an EE-side client that reaches one over SIF (see EE, IOP, and SIF).

Layering

This SDK has two separate register-level SPU2 drivers. Everything else builds on one of them:

core/libsd  ─────┐                     core/libspu2 ─────┐
                 │                                        │
             world/sdr                            world/libsnd2 (MIDI/sequencer)
      (RPC wrapper, IOP)                                  │
                                              world/rspu2drv (RPC, links BOTH
                                               libsnd2 AND libspu2)

• libsd and libspu2 (both core) are independent, register-level SPU2 drivers with direct hardware access. They are separate implementations, not versions of the same driver.
• libsnd2 (world) is a MIDI/sequencer layer built on libspu2.
• rspu2drv (world) is an RPC-exposed driver that statically links both libsnd2 and libspu2.
• sdr (world) is an RPC wrapper around libsd (its IOP binary is sdrdrv.irx).
• ps2snd (core) is the EE-side RPC client for whichever of these IOP drivers is running. Your EE code calls it.
• ahx (core) is a separate EE-side RPC client for the IOP's AHX audio-codec driver (a compressed audio format). It is separate from the SPU2 drivers above.

audio

audio (world) is a higher-level playback API: load a sound, play it on a channel, or feed PCM to a stream for music and video audio. It has an IOP driver, audio.irx, that drives the SPU2 through libsd, and an EE library, libaudio.a, that your code links. It is licensed AFL-2.0, like the rest of the world tier.

• Sounds and channels. audio_sound_load_apcm() uploads an .adp file to SPU2 memory and audio_play_sound() plays it on the first free channel. Each of the 24 channels keeps its own volume, pan and pitch.
• Stream. audio_stream_start() sets a format (8 or 16 bits, mono or stereo, 8000 to 48000 Hz) and audio_stream_queue_pcm() feeds it. The library converts to what the SPU2 plays.
• Effects. The SPU2 has a hardware reverb and delay. audio_effect_set_preset() picks one of ten presets (room, studio, hall, space, echo, delay, pipe and others), and audio_channel_set_effect_send() or audio_stream_set_effect_send() sends a channel or the stream through it. Select the preset before loading sounds: the effect on the stream needs working memory from the same SPU2 RAM.
• Loading the driver. Your program loads libsd.irx and then audio.irx before calling audio_init(). With ps2build, embed_irx: [libsd, "audio:audio"] does it.

Two examples, a sound player and a tone generator, are in the audio/examples folder of sdk-world. The API reference covers every function, the .adp format and the threading rules.

Code written for audsrv

audsrv-compat (world) provides the audsrv API on top of audio, so existing code builds and runs without source changes: link audsrv-compat and embed the driver under the old symbol with embed_irx: [libsd, "audio:audsrv"]. CD audio is not supported and the CD calls return an error. The API reference has a migration guide with one row per audsrv call.

The original audsrv is still available as its own repo, under its own license.

libmad (world) decodes MP3 to raw PCM samples. It feeds audio or one of the lower-level drivers for playback.

Layer summary

Need	Package
Sound effects, music streams, reverb	audio
Voice-level control, custom DSP	libsd, libspu2, ps2snd
MIDI sequencing	libsnd2
MP3 decoding	libmad

See also

• EE, IOP, and SIF - why most packages pair an EE client with an IOP driver
• Packages - the core/world license split