- WMA files were introduced to directly compete with other compressed audio file formats, such as MP3 files and Real Audio files. In the late 1990s, MP3 and Real Audio files became popular ways to compress music files to a fraction of their original size, allowing them to easily be shared over slow Internet connections, including dial-up services. In 1999, Microsoft released the first WMA codec, claiming that it offered better compression and smaller file sizes than the competing compression algorithms.
- By encoding CDs or other audio files into WMA files, the user can archive larger amounts of audio on his computer than if the files were stored in their native WAV format. In addition, WMA files are easier to transfer over the Internet than WAV files, due to their smaller sizes. Unlike some of the competing formats, DRM, or Digital Rights Management, can easily be applied to WMA files, in order to prevent illicit sharing of content.
- Initially, WMA files were encoded only in the original WMA codec, which offers stereo encoding at a variety of constant or variable bit rates. Several years later, Microsoft added a few other codecs to the WMA family. WMA Professional adds support for multiple channel recording, at higher resolutions. WMA Lossless offers audio compression that still maintains a digitally perfect copy of the original work. Finally, WMA Voice offers very high compression for voice-only audio samples, in a single audio channel.
- Standard WMA files can be encoded in mono or stereo, in resolutions up to 48 kHz, or 48,000 samples per second. The files can be encoded either at a constant bit rate, or at a variable bit rate. The WMA Pro codec allows each of the multiple channels to be encoded at up to 96 kHz, which more accurately reproduces the original sound spectrum. WMA Lossless offers encoding for up to six channels, at the same resolution as WMA Pro, but the resulting files are larger due to the lossless compression. WMA Voice reduces the resolution, bit rate, and the number of channels, which allows a smaller file size for voice-only files.
- When choosing to encode audio into WMA files, one must choose the appropriate codec and the appropriate settings in order to reproduce the original content accurately. While the technical settings can be easy to choose, such as the number of channels or the resolution, choosing the bit rate or whether to use lossy or lossless compression will often depend on the listener's preferences. Some people may hear no distortion in a 128 kbs bit rate file encoded with lossy compression, while others may perceive distortion even in a 768 kbs file encoded with lossy compression. Before encoding an entire collection of music, a test should be done at several different bit rates to find the appropriate settings to use.
