What is Windows Media Audio – WMA
Windows Media Audio (WMA) is an audio data compression technology developed by Microsoft. It is a proprietary technology that forms part of the Windows Media framework. WMA consists of four distinct codecs. Each WMA file features a single audio track in one of the four sub-formats: WMA, WMA Pro, WMA Lossless, or WMA Voice. These formats use different codes that are technically distinct and mutually incompatible.[clarify] each codec is further explained below.
Windows Media Audio
Windows Media Audio (WMA) is the most common codec of the four WMA codecs. WMA can encode audio signals sampled at up to 48 kHz with up to two discrete channels (stereo). Like AAC and Ogg Vorbis, WMA was intended to address perceived deficiencies in the MP3 standard. Given their common design goals, the three formats ended up making similar design choices. All three are pure transform codecs.
Windows Media Audio Professional
Windows Media Audio Professional (WMA Pro) is an improved lossy codec closely related to WMA standard. It retains most of the same general coding features, but also features improved entropy coding and quantization strategies as well as more efficient stereo coding. Notably, many of the WMA standard’s low bitrate features have been removed, as the core codec is designed for efficient coding at most bitrates. Its main competitors include AAC, HE-AAC, Vorbis, Dolby Digital, and DTS. It supports 16-bit and 24-bit sample bit depth, sampling rates up to 96 kHz and up to eight discrete channels (7.1 channel surround). WMA Pro also supports dynamic range compression, which reduces the volume difference between the loudest and quietest sounds in the audio track. According to Microsoft’s Amir Majidimehr, WMA Pro can technically go beyond 7.1 surround sound and support “an unlimited number of channels.”
Windows Media Audio Lossless
Windows Media Audio Lossless (WMA Lossless) is a lossless audio codec that competes with ATRAC Advanced Lossless, Dolby TrueHD, DTS-HD Master Audio, Shorten, Monkey’s Audio, FLAC, Apple Lossless, and WavPack (Since late 2011, the last three have the advantage of being open source software and available for nearly any operating system.) Designed for archival purposes, it compresses audio signals without loss of quality from the original using VBR. When decompressed, the audio signal is an exact replica of the original.
Windows Media Audio Voice
Windows Media Audio Voice (WMA Voice) is a lossy audio codec that competes with Speex (used in Microsoft’s own Xbox Live online service), ACELP, and other codecs. Designed for low-bandwidth, voice playback applications, it employs low-pass and high-pass filtering of sound outside the human speech frequency range to achieve higher compression efficiency than WMA. It can automatically detect sections of an audio track containing both voice and music and use the standard WMA compression algorithm instead. WMA Voice supports up to 22.05 kHz for a single channel (mono) only. Encoding is limited to constant bit rate (CBR) and up to 20 kbit/s. The first and only version of the codec is WMA 9 Voice. Windows Mobile-powered devices with Windows Media Player 10 Mobile have native support for WMA 9 Voice playback. In addition, BBC World Service has employed WMA Voice for its Internet radio streaming service.