A format of audio stream coding deployed by Microsoft in 1999, it has been serving as a foundation for Windows Media. Its purpose is to store and distribute audio content. Firstly, it was considered a real alternative for MP3, but then, when ACC appeared, WMA partially lost its significance. It differs fundamentally from MP3 by one realization and can be installed on an equal basis with other system codecs of Windows 9x.

A good compression quality characterizes WMA, and therefore it has been adapted later for many audio players, mobile devices, and Playstations. However, due to excessive closure, files in this format cannot be played back on other platforms with satisfactory quality. The new version allows for multi-channel coding of large audio files and coding of voice data. In addition to that, the delay in coding has been significantly diminished thanks to the technology of reduced time dilation.

The name of WMA is being used simultaneously for the file format and the codec. There are some types of the format:

• WMA, a close analog for MP3;
• WMA Pro, high-quality sound files with a wide range of channels;
• WMA Lossless, for lossless compression;
• WMA Voice, for compression of voice content into low bitrate files.

According to Microsoft programmers, an audio file of 64 Kbit/s bitrate has a similar sound clarity as the tracks from the original CD. However, some of advanced users do not share such views. Most often, WMA files are generated in Advanced Systems Format which contains both audio and video content. One of the failures is the impossibility to support bitrate of more than 160Kbit/s.

MP3 (formally MPEG-1 Audio Layer-3 or MPEG-2 Audio Layer-3) is a digital format for storing audio files and audio streaming. MPEG programmers designed the format. It is one of the most required codecs for digital coding. The format is widely used in various file-sharing sites for evaluation downloading.

Due to lossy compression in this audio format, it is possible to compress CD tracks up to 1/10 of their original size while maintaining high playback quality. Moreover, it can be encoded at higher or lower bit rates to adjust the resulting quality. Overtones, which cannot be perceived by a human ear, are removed. Complex algorithms allow for a smaller size of tracks. As a result, one compact disk can contain several hundred songs. MP3 is compatible with all the most popular operating systems and is supported by most modern DVD-players and music systems.

Before MP3 introduction, MPEG-1 had been widely used. That format contained not only audio data but images as well. MP3 breaks an audio file into parts of the same length. When the processing is over, each part is packed into its frame. It involves the spectral limit technology that requires a continuous input signal to provide the use of two adjacent structures.

When spectral deleting is over, the file is to be compressed with mathematic methods. If necessary, the compression rate can be changed, even inside the same frame. Files of 128 kbit/s have 11-fold compression. Further reduction of the file size will lead to a significant deterioration in sound quality.