Audio Files
As with Meshes or Textures, the workflow for Audio File assets is designed to smooth and trouble free. Unity can import almost every common file format but there are a few details that are useful to be aware of when working with Audio Files.
Audio in Unity is either Native or Compressed. Unity supports most common formats (see the list below) and will import an audio file when it is added to the project. The default mode is Native, where the audio data from the original file is imported unchanged. However, Unity can also compress the audio data on import, simply by enabling the Compressed option in the importer. (iOS projects can make use of the hardware decoder - see the iOS documentation for further details). The difference between Native and Compressed modes are as follows:-
- Native: Use Native (WAV, AIFF) audio for short sound effects. The audio data will be larger but sounds won't need to be decoded at runtime.
- Compressed: The audio data will be small but will need to be decompressed at runtime, which entails a processing overhead. Depending on the target, Unity will encode the audio to either Ogg Vorbis(Mac/PC/Consoles) or MP3 (Mobile platforms). For the best sound quality, supply the audio in an uncompressed format such as WAV or AIFF (containing PCM data) and let Unity do the encoding. If you are targeting Mac and PC platforms only (including both standalones and webplayers) then importing an Ogg Vorbis file will not degrade the quality. However, on mobile platforms, Ogg Vorbis and MP3 files will be re-encoded to MP3 on import, which will introduce a slight quality degradation.
Any Audio File imported into Unity is available from scripts as an Audio Clip instance, which is effectively just a container for the audio data. The clips must be used in conjunction with Audio Sources and an Audio Listener in order to actually generate sound. When you attach your clip to an object in the game, it adds an Audio Source component to the object, which has Volume, Pitch and a numerous other properties. While a Source is playing, an Audio Listener can "hear" all sources within range, and the combination of those sources gives the sound that will actually be heard through the speakers. There can be only one Audio Listener in your scene, and this is usually attached to the Main Camera.
Supported Formats
| Format | Compressed as (Mac/PC) | Compressed as (Mobile) |
|---|---|---|
| MPEG(1/2/3) | Ogg Vorbis | MP3 |
| Ogg Vorbis | Ogg Vorbis | MP3 |
| WAV | Ogg Vorbis | MP3 |
| AIFF | Ogg Vorbis | MP3 |
| MOD | - | - |
| IT | - | - |
| S3M | - | - |
| XM | - | - |
See the Sound chapter in the Creating Gameplay section of this manual for more information on using sound in Unity.
Audio Clip
Audio Clips contain the audio data used by Audio Sources. Unity supports mono, stereo and multichannel audio assets (up to eight channels). The audio file formats that Unity can import are .aif, .wav, .mp3, and .ogg. Unity can also import tracker modules in the .xm, .mod, .it, and .s3m formats. The tracker module assets behave the same way as any other audio assets in Unity although no waveform preview is available in the asset import inspector.
The Audio Clip Inspector
Properties
| Audio Format | The specific format that will be used for the sound at runtime. |
| Native | This option offers higher quality at the expense of larger file size and is best for very short sound effects. |
| Compressed | The compression results in smaller files but with somewhat lower quality compared to native audio. This format is best for medium length sound effects and music. |
| 3D Sound | If enabled, the sound will play back in 3D space. Both Mono and Stereo sounds can be played in 3D. |
| Force to mono | If enabled, the audio clip will be down-mixed to a single channel sound. |
| Load Type | The method Unity uses to load audio assets at runtime. |
| Decompress on load | Audio files will be decompressed as soon as they are loaded. Use this option for smaller compressed sounds to avoid the performance overhead of decompressing on the fly. Be aware that decompressing sounds on load will use about ten times more memory than keeping them compressed, so don't use this option for large files. |
| Compressed in memory | Keep sounds compressed in memory and decompress while playing. This option has a slight performance overhead (especially for Ogg/Vorbis compressed files) so only use it for bigger files where decompression on load would use a prohibitive amount of memory. |
| Stream from disc | Stream audio data directly from disc. The memory used by this option is typically a small fraction of the file size, so it is very useful for music or other very long tracks. For performance reasons, it is usually advisable to stream only one or two files from disc at a time but the of streams that can comfortably be handled depends on the hardware. |
| Compression | Amount of Compression to be applied to a Compressed clip. Statistics about the file size can be seen under the slider. A good approach to tuning this value is to drag the slider to a place that leaves the playback "good enough" while keeping the file small enough for your distribution requirements. |
| Hardware Decoding | (iOS only) On iOS devices, Apple's hardware decoder can be used resulting in lower CPU overhead during decompression. Check out platform specific details for more info. |
| Gapless looping | (Android/iOS only) Use this when compressing a seamless looping audio source file (in a non-compressed PCM format) to ensure perfect continuity is preserved at the seam. Standard MPEG encoders introduce a short silence at the loop point, which will be audible as a brief "click" or "pop". |
Importing Audio Assets
Unity supports both Compressed and Native Audio. Any type of file (except MP3/Ogg Vorbis) will be initially imported as Native. Compressed audio files must be decompressed by the CPU while the game is running, but have smaller file size. If Stream is checked the audio is decompressed on the fly, otherwise it is decompressed completely as soon as it loads. Native PCM formats (WAV, AIFF) have the benefit of giving higher fidelity without increasing the CPU overhead, but files in these formats are typically much larger than compressed files. Module files (.mod,.it,.s3m..xm) can deliver very high quality with an extremely low footprint.
As a general rule of thumb, Compressed audio (or modules) are best for long files like background music or dialog, while Native is better for short sound effects. You should tweak the amount of Compression using the compression slider. Start with high compression and gradually reduce the setting to the point where the loss of sound quality is perceptible. Then, increase it again slightly until the perceived loss of quality disappears.
Using 3D Audio
If an audio clip is marked as a 3D Sound then it will be played back so as to simulate its position in the game world's 3D space. 3D sounds emulate the distance and location of sounds by attenuating volume and panning across speakers. Both mono and multiple channel sounds can be positioned in 3D. For multiple channel audio, use the spread option on the Audio Source to spread and split out the discrete channels in speaker space. Unity offers a variety of options to control and fine-tune the audio behavior in 3D space - see the Audio Source component reference for further details.
Platform specific details
iOS
On mobile platforms compressed audio is encoded as MP3 to take advantage of hardware decompression.
To improve performance, audio clips can be played back using the Apple hardware codec. To enable this option, check the "Hardware Decoding" checkbox in the Audio Importer. Note that only one hardware audio stream can be decompressed at a time, including the background iPod audio.
If the hardware decoder is not available, the decompression will fall back on the software decoder (on iPhone 3GS or later, Apple's software decoder is used in preference to Unity's own decoder (FMOD)).
Android
On mobile platforms compressed audio is encoded as MP3 to take advantage of hardware decompression.