Windows Media Audio

Windows Media Audio (WMA) is an audio compression technology developed by Microsoft. The name can be used to refer to the audio file format or the audio codec. It is proprietary software that is part of the Windows Media suite.

WMA consists of four different codecs. The original WMA codec, known simply as WMA, was intended as a competitor to MP3 and RealAudio. A more modern and advanced codec, WMA Pro supports surround audio and There is also a lossless compression format, WMA Lossless, which compresses audio without losing definition (regular WMA has lossy compression). There is another variation called WMA Focused on spoken content, Voice applies compression and is designed for very low bit rates.

Sound quality

Microsoft also claims that audio encoded with WMA at lower bitrates has better quality than MP3 encoded at higher bitrates. Double-blind listening tests with other lossy audio codecs show mixed results, some disproving the claims from Microsoft, others checking them. An independent test done in May 2004 with a bit rate of 128 kbit/s showed that WMA is equivalent to LAME MP3; inferior to AAC and Vorbis; and superior to ATRAC3.

Some conclusions made by recent studies:

• A 32 kbit/s (breakable link available on the Internet Archive; see history, first version and last).WMA was notably better than LAME MP3, but not better than other modern codecs, in an independent test done in July 2004.
• A 48 kbit/s, WMA 10 Pro was appointed second after the HE-AAC Nero and better than WMA 9.2 in an independent listening test organized by Sebastián Mares and Hydrogenaudio Forum in December 2006. This test, however, used CBR for WMA 10 Pro and VBR for the other codecs.
• A 64 kbit/s, WMA Pro beat the Nero HE-AAC in an independent test by National Software Testing Labs in 2005. Of the 300 participants, "71% indicated that WMA Pro was of equal or better quality than HE AAC."
• At 80 kbit/s and 96 kbit/s, WMA had worse quality than HE-AAC, AAC-LC, and Vorbis; equivalent to MP3, and with better quality than MPC in individual tests performed in 2005.
• At 128 kbit/s, there is a tie between aoTuV Vorbis, LAME MP3, WMA 9 Pro and AAC in a large-scale test performed in January 2006, with each codec having a sound quality fenced to that of uncompressed sound for most participants.
• At 768 kbit/s, WMA 9 Pro delivered full-spectrum response to half of the bit rate required by DTS in a comparative test done by EDN in October 2003. The test was made with a sound sample at 48 kHz, 5.1 surround channels.

Criticism of the attributed quality

There has been much criticism of Microsoft's repeated claims of codec quality. An article in MP3 Developments states that the sound of a CD and a 64 kbit/s WMA audio file does not compare.

WMA and MP3 are considered equivalent to a bit rate of 192 kbit/s. In 1999 a study funded by Microsoft, National Software Testing Laboratories (NSTL) found that WMA encoded at 64 kbit/s was preferable to MP3 at 128 kbit/s (encoded with Musicmatch Jukebox). However, a public test conducted in September 2003 by Roberto Amorim concluded that participants preferred 128 kbit/s MP3 audio over 64 kbit/s WMA audio with a 99% Confidence Interval. This conclusion applies equally to other codecs with the same bitrate, leading Amorim to conclude:

No codec gives the same sound quality as the MP3 at half of its bit rates.

It's important to note that both encoders have been under active development and have improved over the years, so their relative quality may vary over time.

A public test conducted in July 2007 by Sebastián Mares found that HE-AAC audio encoded at 64 kbit/s (using Nero Digital) is statistically tied with WMA Pro at 64 kbit/s, in terms of user preference. participant.