Windows Media Audio (WMA) is an audio codec (in addition to an audio container format) developed by Microsoft Corporation to end MP3’s hegemony as the standard codec for consumer audio. In fact, the format promised the Same quality as MP3 using only half the bitrate and, in addition, it claimed to achieve CD-Audio quality with a bitrate of only 64Kbps.
Files encoded with this codec and stored in the WMA container have the .wma extension.
It was created in the late 90’s at the Microsoft Signal Processing Center and was initially known as MSAudio 4.0 (released in 1999) and later renamed WMA version 1. Numerous versions followed one another until reaching the current version, version 9. (released in 2003). Today it is one of the most popular because it is the standard format of the Windows Media player (included in the ubiquitous Windows operating system), one of the most popular at the user level. This program allows both the reproduction and the creation of files (only from version 7 of this program) encoded with this format. It is also the standard format for the Zune Portable audio player, the popular competitor to Apple’s even more popular Ipod.
Currently there are 4 different versions of Windows Media Audio:
Windows Media Audio: Currently in its version 9 (released in 2003) it is the best known of the 4 codecs that make up the WMA family. It is a lossy codec that bases the elimination of information from the original signal on psychoacoustics and the “defects” of the human ear (those sounds that are considered inaudible are eliminated in the coding process). If the bitrate is low, a lot of information from the original signal will have to be discarded which can cause the sound of the signal encoded in wma to be different from the original and present some errors.
To implement WMA coding, a sampling rate of up to 48,000Hz is used with two independent stereo channels, variable bitrate (VBR, which assigns a higher bitrate to the more complex sections (transitions from bass to treble faster, sudden volume changes etc)) and the average bitrate technique in which not all sections are transmitted to the same bitrate (as in VBR) but in every second the same information is always transmitted in total (as with bitrate constant) .Thanks to these 2 techniques we will have the same quality throughout the audio file. Both VBR and medium bitrate are only available as of WMA 9.
In addition there is a low delay version (only from WMA 9.1) for bidirectional (Full-duplex) applications such as VoIP.
Like the rest of the audio codecs for music such as MP3, Vorbis, AAC or ATRAC, it is based on the Modified Discrete Cosine Transform (MDCT) to transform the signal from the temporal domain to the frequency one. Finally, the samples are encoded with the Huffman algorithm. In addition, a joint audio technique known as stereo M / S encoding is used (see description) .In addition, when the bitrate is extremely low, sample prediction techniques such as LSP (Line Spectral Pairs) or LSF (Line Spectral Frequencies) are used. .
All these characteristics are reflected in the conclusions of some studies on audio codecs:
For a 32Kbps bitrate the quality is better than that of its direct competitor: Mp3.
For 48kbps bitrate the WMA Pro quality is the second best of all codecs, just behind HE-AAC version 2.
At 64Kbps WMA Pro Bitrate Outperforms HE-AAC in Quality
At a bitrate of 80Kbps and 96Kbps WMA lost in quality compared to HE-AAC, Vorbis and AAC-LC
At 128Kbps the quality of WMA Pro is equal to that of its competitors AAC, MP3 and Vorbis
At 768Kbps bitrate WMA Pro gets spectral response across the spectrum while DTS (Digital Theater Systems) needs twice the bitrate to do it. At these high bitrates, all lossy codecs achieve transparency, that is, a totally perfect quality where the differences from the original signal are imperceptible to the human ear.
For a much more extensive comparison, SoundExpert can be consulted.
Being a format developed by a multinational as powerful as Microsoft, almost all the players allow you to work with WMA, both portable, desktop and computer players, although the ideal WMA environment is to use the Zune portable player and the player for the Windows operating system, Windows Media player (its latest version is 11).
One of the most controversial aspects of the format is that it incorporates DRM (Digital Rights Management), which limits the distribution of copyrighted files encoded with this format.
