Developed by the Signal Processing Group at Microsoft, the WMA file format is part of the Windows Media framework and was first released commercially in 1999, with support for playback of WMA encoded files as part of Windows Media Player. Creation of WMA files did not come until Windows Media Player version 7. The original codec was targeted as a direct competitor to the MP3 and RealAudio formats, and has achieved a broad level of adoption thanks to support for playback on numerous DVD players, Nokia mobile handsets and Playstation portable devices.
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 as a real alternative for MP3, but then, when ACC appeared, WMA lost partially 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.
WMA is characterized by a good compression quality, 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.
In almost all circumstances WMA files are part of the Advanced Systems Format (ASF) container, a proprietary container format developed by Microsoft for both digital video and digital audio. Every WMA file contains an audio track encoded in one of four mutually distinct codecs - WMA, WMA Voice, WMA Lossless or WMA Pro - WMA is the most commonly found of the four, but is a lossy codec, with the ability to encode audio signals sampled at up to 48 kHz. WMA Pro is an improved version, allowing sampling up to 96 kHz, but has achieved little hardware and software support. WMA Lossless is designed to compress audio signals with no loss of quality from the original source (up to 96 kHz) and is used in some Windows Mobile devices as well as the Logitech Squeezebox Touch. Finally, WMA Voice is a lossy codec optimized for low-bandwith voice playback applications, with mono sampling support up to 22.05 kHz - it is perhaps most well known for being used by the BBC World service for streaming Internet radio.
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 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 is a digital music format which allows CD tracks to be reduced to around a tenth of their normal size without a significant loss of quality. MP3 gets rid of a lot of the information recorded in a song that our ears are not able to hear and then uses complex algorithms to reduce the file size. This then enables you to get hundreds of songs on to a CD and it also has opened up a new market over the internet - the download market as download times have been significantly reduced.
MP3 is a digital format for storage of audio files designed by MPEG programmers. It is one of the most required codecs for digital coding. The format is widely used in various file-sharing sites for evaluation downloading.
With this format, it is possible to compress CD tracks up to 1/10 of their original size while maintaining high playback quality. Overtones, which cannot be perceived by a human ear, are removed. Complex algorithms allow for smaller size of tracks. As a result, one compact disk can contain several hundred songs. MP3 is compatible with all most popular operating systems and supported by the most of modern DVD-players and music systems.
The MP3 format is a lossy format. That means that an MP3 file does not contain 100% of the original audio information. Instead, MP3 files use perceptual coding. In other words, that means it removes the information that your ear doesn't notice thereby making the file smaller. The reason lossy formats are used over RAW is that RAW audio files are too large to travel over the internet at any great speed. By using lossy formats it enables even dial up users to download mp3 files at a reasonable speed. RAW file formats generally require 176,000 bytes per second compared to a lossy format which requires 17,600. The difference is massive and so are the download times.
Prior to 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 own frame. It involves the technology of spectral limit that requires a continuous input signal to provide the use of two adjacent frames.
When spectral deleting is over, the file is to be compressed with mathematic methods. If necessary, 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 significant deterioration in sound quality.
Moving Picture Experts Group