MPC, or 'Musepack', is an open source optimized version of the MPEG-1 Audio Layer 2 / MP2 lossy audio compression format. Open source refers to projects that are open to the public and which draw on other projects that are freely available to the general public. ... MP2, also known as Musicam, is a short form of MPEG-1 Audio Layer 2 (not MPEG-2), and it is also used as a file extension for files containing audio data of this type. ... Note: This article is about audio data compression, which reduces the data rate of digital audio signals. ...

Unlike MPEG-1 Layer II, it uses:

• subband-wise selectable M/S encoding (like AAC)
• Huffman coding (like MPEG Layer III, AAC, ...)
• noise substitution techniques as used in ATSC A-52 and MPEG-4 AAC V2
• pure variable bitrate between 3 and 1300 kbit/s (when needed)

The psychoacoustic model of MPC is based on MPEG ISO model 2, but is extended by CVD (clear voice detection). The quantization algorithm of the MPC encoder performs spectral shaping of the noise, called adaptive noise shaping (ANS), in order to overcome the low frequency resolution of the polyphase quadrature filter bands. Advanced Audio Coding (AAC) is a lossy data compression scheme intended for audio streams. ... In computer science, Huffman coding is an entropy encoding algorithm used for lossless data compression. ... Psychoacoustics is the study of subjective human perception of sounds. ... A polyphase quadrature filter, or PQF is a filter bank, which splits an input signal into a given number N (mostly a power of 2) of equidistant sub-bands. ...

In May 2004, a series of double-blind listening tests [1] (http://www.rjamorim.com/test/multiformat128/results.html) (as reported on Slashdot [2] (http://slashdot.org/articles/04/05/24/0623247.shtml?tid=141&tid=185&tid=188)) suggested that Musepack and Ogg Vorbis 1.1 (which was the "aoTuV" fork at the time) would be the two best available lossy codec for high-quality audio compression at bitrates around 128kbit/s, compared with MP3, AAC, WMA, or ATRAC. Other listening tests have also rated MPC highly. However, most of those following tests are in medium/low bitrate area, for which mpc hasn't been designed. And so they aren't really informative on musepack goal, which is to obtain 100% transparency at --standard setting (~160-180kbits average). Double-blind describes an especially stringent way of conducting an experiment, usually on living, conscious, human subjects. ... Vorbis is an open and free audio compression (codec) project from the Xiph. ... A lossy data compression method is one where compressing a file and then decompressing it retrieves a file that may well be different to the original, but is close enough to be useful in some way. ... Codec is a portmanteau of coder/decoder, which describes a device or program capable of performing transformations on a data stream or signal. ... MP3 is a popular digital audio encoding and lossy compression format. ... Advanced Audio Coding (AAC) is a lossy data compression scheme intended for audio streams. ... Windows Media Audio (WMA) is a proprietary compressed audio file format developed by Microsoft. ... ATRAC (Adaptive TRansform Acoustic Coding) is an audio compression algorithm used to store information on Minidiscs and other Sony-branded audio players. ...

Listening tests of MPC:

• 2004 - rjamorim's second 128 kbit/s group listening test [3] (http://www.rjamorim.com/test/multiformat128/results.html) - between 14 and 27 listeners. MPC and Vorbis tied for first.
• 2003 - rjamorim's 128 kbit/s group listening test [4] (http://www.rjamorim.com/test/128extension/results.html) - between 14 and 29 listeners. AAC, MPC, Vorbis, and WMA tied for first.
• 2002 - ff123's second 128 kbit/s group listening test [5] (http://ff123.net/128test/instruct.html)
• 2001 - ff123's 128 kbit/s group listening test [6] (http://ff123.net/128tests.html)
• 2004 - High bitrate tests [7] (http://www.hydrogenaudio.org/forums/index.php?showtopic=18397) (thread by a Musepack developer)

Development of MPC was initiated in 1997 by Andree Buschmann and later taken over by Frank Klemm, and is currently maintained by the Musepack Development Team (MDT) with assistance from Frank Klemm.

Encoders and Decoders are available for Microsoft Windows, Linux and Mac OS X free of charge, mostly licensed as free software under the LGPL or BSD license. They are distributed via the MPC project's website (see external link below). Many third-party programs (audio players, CD rippers etc.) support MPC, either directly or via plugins. Microsoft Windows is a range of closed source proprietary commercial operating environments for personal computers and servers. ... Tux, a penguin, is the official Linux mascot. ... Mac OS X is the latest version of the Mac OS, the operating system software for Macintosh computers. ... Free software, as defined by the Free Software Foundation (FSF), is software which is free as in freedom, not as in beer (also referred to as libre or freedom software). ... GNU logo The GNU Lesser General Public License (formerly the GNU Library General Public License) is an FSF approved Free Software license designed as a compromise between the GNU General Public License and simple permissive licenses such as the BSD license and the MIT License. ... The BSD license is the license agreement that the BSD software (largely, a version of UNIX) is distributed under. ... The front page of the English Wikipedia website. ... A CD ripper, CD grabber or CD extractor is a piece of software designed to extract raw digital audio (in format commonly called CDDA) from a compact disc to a file or other output. ... A plugin (or plug-in) is a computer program that can, or must, interact with another program to provide a certain, usually very specific, function. ...

MPC uses the APEv2 tag metadata container. The APEv2 tag was originally developed for the Monkeys Audio file format as a metadata container for such information as the title, artist, album, track number or other information about the file to be added to the file itself (See APEv2 spec or cached APEv2 spec) but has emerged... Metadata (Greek: meta-+data information) means While this definition is commonly offered, it is also commonly not helpful. ...

In the past, MPC has been under suspicion of violating multiple patents (MP2, PNS, subband) [8] (http://www.hydrogenaudio.org/forums/index.php?showtopic=6473). According to the developers of MPC, all patented code has been removed and it is now believed to be free of patent encumbrance. However, one PNS patent application is still active [9] (http://appft1.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PG01&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.html&r=1&f=G&l=50&s1=%2220050004791%22.PGNR.&OS=DN/20050004791&RS=DN/20050004791), and it is not trivial to know if MPC's own "noise substitution techniques" avoids its scope or not. Only a careful examination by a patent lawyer would say whether Musepack is truly patentless or not.

External links

• Musepack.net (http://www.musepack.net) Official website of the Musepack project (encoders, decoders, XMMS, Beep Media Player, Winamp plugins, forums)
• Frank Klemm's MPC page (http://xmixahlx.dyndns.org/audio/files/linux/musepack/klemm/www.personal.uni-jena.de/~pfk/mpp/) (mirror)
• Musepack forum (http://www.hydrogenaudio.org/forums/index.php?showforum=56) at Hydrogenaudio.org
• Pymusepack (http://www.sacredchao.net/quodlibet) Python bindings for libmpcdec (BSD decoder library). Used by Quod Libet