A BIT file is an .MP3 audio file with the .bit file extension, which was used in the early 1990s before being replaced by the .mp3 extension in 1995. It is saved in a compressed MPEG format that uses "Layer 3" audio compression (MP3) to reduce its file size without losing much quality. BIT files are most often used to save songs, but may also store other types of audio recordings, such as interviews or narrations.
The MP3 format was originally released in 1993 by the Moving Picture Experts Group (MPEG) and the .bit file extension was initially assigned to MP3 audio files. However, in 1995, researchers at the Fraunhofer Institute for Integrated Circuits (Fraunhofer IIS) changed the extension to .mp3 when they released their MP3 encoding technology, "l3enc." Fraunhofer IIS then released WinPlay3 for Windows in September 1995, which enabled users to encode and playback MP3 files.
MP3 soon became the standard format for storing music since it could compress audio to a fraction of the size of other common audio file formats at the time, such as .WAV and .AIF files, without significant loss in quality. This was especially important due to the limited storage space offered by computer hard drives at the time.
Since the .bit extension was used before the MP3 format became widely adopted, you will most likely never encounter a BIT audio file. However, if you do come across a BIT file you can play it with an audio player that supports the MP3 format, such as Microsoft Windows Media Player, Apple iTunes, or VideoLAN VLC media player.
NOTE: If you are unable to open a BIT file with an audio player that supports the MP3 format, you may have to manually change the .bit file extension to .mp3.