The default mode is Compressed, where the audio data is compressed with either Vorbis/MP3 for standalone and mobile platforms, or HEVAG/XMA for PS Vita and Xbox One. Unity supports most common formats for importing audio (see the list below) and will import an audio file when it is added to the project. Additionally there are a few platform-specific formats, but they work in similar ways.

When audio is encoded in Unity the main options for how it is stored on disk is either PCM, ADPCM or Compressed. footsteps, weapons and impacts), while other assets may be loaded on demand or gradually as the player progresses through the level (speech, background music, ambience loops etc). This means that you have great flexibility for deciding which audio assets should be kept in memory at all times (because you may not be able to predict how often or how fast they will be playing, i.e. The AudioClips merely refer to the files containing the audio data and there are various combinations of options in the AudioClip importer that determine how the clips are loaded at runtime. Since Unity 5.0 audio data is separated from the actual AudioClips.

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. As with Meshes or Textures, the workflow for Audio File assets is designed to be smooth and trouble free.

Extract audio files from .unity3d