Audio system

DSP emulation and audio processing with HLE and LLE backends

Dolphin emulates the GameCube/Wii Digital Signal Processor (DSP) which handles all audio processing.

DSP Hardware

The DSP is a dedicated audio coprocessor:

Feature	Value
Clock Speed	81 MHz
Architecture	Custom 16-bit DSP
IRAM	8192 x 16-bit instructions
DRAM	4096 x 16-bit data words
DMA	Bidirectional to main RAM

Location: Source/Core/Core/DSP/

Emulation Modes

Dolphin supports two DSP emulation approaches:

HLE (High-Level)

Location: Core/DSP/DSPHLE/

Default and recommended. Emulates DSP behavior without running actual DSP code:

Advantages

• Very fast (low CPU usage)
• No DSP ROM required
• Compatible with 95%+ of games
• Deterministic

How It Works

• Intercepts DSP UCode (microcode) uploads
• Identifies known UCode types (AX, Zelda, etc.)
• Reimplements UCode functionality in C++
• Outputs audio samples directly

Supported UCodes

• AX: Most common (Luigi’s Mansion, Mario Kart, etc.)
• Zelda: Zelda-specific (Wind Waker, Twilight Princess)
• Card: Memory card operations
• InitAudioSystem: Boot-time initialization
• ROM: IPL/BIOS DSP code

[DSP]
EnableJIT = True  # Irrelevant for HLE
Backend = HLE     # Default

LLE (Low-Level)

Location: Core/DSP/DSPLLE/

Accurately emulates the DSP hardware by running actual DSP code:

Advantages

• Near-perfect accuracy
• Supports custom DSP code
• Required for some games (< 5%)

Disadvantages

• Higher CPU usage (10-30% more)
• Requires DSP ROM files
• Potential audio glitches if too slow

DSP ROM Files

Required files in User/GC/USA/ (or region equivalent):

• dsp_rom.bin (8 KB DSP instruction ROM)
• dsp_coef.bin (4 KB coefficient ROM)

Execution Backends

LLE Interpreter

Interprets each DSP instruction:

• Slowest LLE option
• Simplest and most accurate
• Used for DSP debugging

[DSP]
EnableJIT = False
Backend = LLE

LLE JIT Recompiler

Compiles DSP code to native x86-64:

• 3-5x faster than interpreter
• Still accurate
• Recommended LLE mode

[DSP]  
EnableJIT = True
Backend = LLE

Audio Pipeline

Audio flows through these stages:

1. Game Sends Audio Commands

   PowerPC CPU sends commands to DSP via mail interface

   Location: Core/DSP/DSP.cpp

   • Write to DSP mailbox registers
   • Upload UCode to IRAM
   • Send DMA commands for audio buffers
2. DSP Processes Audio

   DSP runs UCode to process samples

   HLE: C++ implementation mimics UCode LLE: Execute actual DSP instructions

   • Decode audio (ADPCM, PCM)
   • Apply effects (reverb, delay, filters)
   • Mix multiple channels
   • Output to DMA buffer
3. Audio Interface Streams

   Audio Interface (AI) streams from DMA buffer

   Location: Core/HW/AudioInterface.cpp

   • 32 KHz sample rate (AI default)
   • Stereo output (left/right channels)
   • Trigger AI interrupts on buffer completion
4. Audio Backend Outputs

   Backend plays samples through OS audio API

   Location: AudioCommon/

   • Resample if needed
   • Send to audio device
   • Handle buffer underruns

Audio Backends

Location: Source/Core/AudioCommon/

Dolphin supports multiple audio output backends:

Backend	Platforms	Description
Cubeb	All	Cross-platform (recommended)
WASAPI	Windows	Windows Audio Session API
PulseAudio	Linux	Linux standard
ALSA	Linux	Advanced Linux Sound Architecture
OpenAL	All	OpenAL Soft
OpenSLES	Android	Android native audio
Null	All	No output (testing)

Configuration

[DSP]
Backend = Cubeb       # Audio backend to use
Volume = 100          # Volume (0-100)
AudioLatency = 20     # Latency in ms (lower = less delay, more CPU)
EnableJIT = True      # DSP JIT (LLE only)

Cubeb (Recommended)

Mozilla’s cross-platform audio library:

[DSP]  
Backend = Cubeb
AudioLatency = 20  # 20ms recommended

Advantages:

• Low latency
• Reliable on all platforms
• Automatic device switching
• Minimal CPU overhead

Audio Settings

Key audio configuration options:

DSP Emulation Engine

Choose between HLE and LLE:

[Core]
DSPHLE = True   # True for HLE, False for LLE

[DSP]
EnableJIT = True  # LLE JIT compilation

Default: HLE (fast, compatible) Use LLE when: Game has audio issues with HLE

Audio Latency

Buffer size in milliseconds:

[DSP]
AudioLatency = 20  # 10-100ms

• Lower (10-20ms): Less delay, more CPU, potential underruns
• Higher (50-100ms): More delay, less CPU, smoother audio

Default: 20ms (good balance)

Stretching

Time-stretch audio to match emulation speed:

[DSP]
AudioStretch = False
StretchFactor = 1.0

Useful when emulation runs slower than 100% speed.

DPL II Decoding

Dolby Pro Logic II decoder:

[DSP]
EnableDPL2 = False  # 5.1 surround from stereo
DPL2Quality = 2     # 0=low, 1=normal, 2=high

Upmixes stereo to 5.1 surround.

DSP UCode Types

Common UCode implementations in HLE:

AX UCode

Location: Core/DSP/DSPHLE/UCodes/AX.cpp

Most common UCode for game audio:

• Multiple voice channels (up to 64)
• ADPCM and PCM decoding
• Volume, pitch, and pan control
• Effects: reverb, chorus, delay
• Surround positioning

Games using AX:

• Luigi’s Mansion
• Mario Kart: Double Dash
• Super Smash Bros. Melee
• Most GameCube/Wii games

Zelda UCode

Location: Core/DSP/DSPHLE/UCodes/Zelda.cpp

Zelda-specific audio:

• Sequenced music playback
• Sound effect triggering
• Custom mixing

Games using Zelda UCode:

• The Legend of Zelda: Wind Waker
• The Legend of Zelda: Twilight Princess
• The Legend of Zelda: Four Swords Adventures

Card UCode

Memory card audio operations (beeps).

Audio Debugging

Enable audio logging:

[Logging]
EnableLogs = True
LOGSP1 = True    # Audio Interface
LOGDSP = True    # DSP
LOGAudio = True  # Audio backend

DSP debugging tools:

# Dump DSP UCode to file
[DSP]
DumpUCode = True

# Dump audio to WAV files  
[DSP]
DumpAudio = True

Files written to User/Dump/Audio/ and User/Dump/DSP/.

Performance Tuning

Fast Performance

[Core]
DSPHLE = True         # Use HLE

[DSP]
Backend = Cubeb       # Efficient backend
AudioLatency = 50     # Higher latency
EnableDPL2 = False    # Disable surround

Low Latency

[Core]  
DSPHLE = True

[DSP]
Backend = Cubeb
AudioLatency = 10     # Minimal latency
EnableJIT = True      # If using LLE

Accuracy

[Core]
DSPHLE = False        # Use LLE

[DSP]
EnableJIT = True      # LLE with JIT
AudioLatency = 20
Backend = Cubeb

See Also

• Audio Settings Guide
• Core Emulation
• Configuration