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Musepack
Musepack or MPC is an open source lossy audio codec, specifically optimized for transparent compression of stereo audio at bitrates of 160–180 (manual set allows bitrates up to 320) kbit/s. It was formerly known as MPEGplus, MPEG+ or MP+. Development of MPC was initiated in 1997 by Andree Buschmann and later assumed by Frank Klemm, and as of 2004 is maintained by the Musepack Development Team (MDT) with assistance from Buschmann and Klemm. Encoders and decoders are available for Microsoft Windows, Linux and Mac OS X, and plugins for several third-party media players available from the Musepack website, licensed under the GNU Lesser General Public License (LGPL) or BSD licenses, and an extensive list of programs supporting the format. Technical details Musepack was developed using the MP2 codec as a starting point, but many features have since been added, including: * subband selectable M/S encoding (as in AAC) * Huffman coding (as in MP3 and AAC, but more efficient). ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Codec Listening Test
A codec listening test is a scientific study designed to compare two or more lossy audio codecs, usually with respect to perceived fidelity or compression efficiency. Most tests take the form of a double-blind comparison. Commonly used methods are known as " ABX" or "ABC/HR" or "MUSHRA". There are various software packages available for individuals to perform this type of testing themselves with minimal assistance. Testing methods ABX test In an ABX test, the listener has to identify an unknown sample X as being A or B, with A (usually the original) and B (usually the encoded version) available for reference. The outcome of a test must be statistically significant. This setup ensures that the listener is not biased by his/her expectations, and that the outcome is not likely to be the result of chance. If sample X cannot be determined reliably with a low p-value in a predetermined number of trials, then the null hypothesis cannot be rejected and it cannot be proved that t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Audio File Format
An audio file format is a file format for storing digital audio data on a computer system. The bit layout of the audio data (excluding metadata) is called the audio coding format and can be uncompressed, or compressed to reduce the file size, often using lossy compression. The data can be a raw bitstream in an audio coding format, but it is usually embedded in a container format or an audio data format with defined storage layer. Format types It is important to distinguish between the audio coding format, the container containing the raw audio data, and an audio codec. A codec performs the encoding and decoding of the raw audio data while this encoded data is (usually) stored in a container file. Although most audio file formats support only one type of audio coding data (created with an audio coder), a multimedia container format (as Matroska or AVI) may support multiple types of audio and video data. There are three major groups of audio file formats: * Uncompressed au ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Windows Media Audio
Windows Media Audio (WMA) is a series of audio codecs and their corresponding audio coding formats developed by Microsoft. It is a proprietary technology that forms part of the Windows Media framework. WMA consists of four distinct codecs. The original WMA codec, known simply as ''WMA'', was conceived as a competitor to the popular MP3 and RealAudio codecs. ''WMA Pro'', a newer and more advanced codec, supports multichannel and high resolution audio. A lossless codec, ''WMA Lossless'', compresses audio data without loss of audio fidelity (the regular WMA format is lossy). ''WMA Voice'', targeted at voice content, applies compression using a range of low bit rates. Microsoft has also developed a digital container format called Advanced Systems Format to store audio encoded by WMA. Development history The first WMA codec was based on earlier work by Henrique Malvar and his team which was transferred to the Windows Media team at Microsoft. Malvar was a senior researcher and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
MP2 (format)
MPEG-1 Audio Layer II or MPEG-2 Audio Layer II (MP2, sometimes incorrectly called Musicam or MUSICAM) is a lossy audio compression format defined by ISO/IEC 11172-3 alongside MPEG-1 Audio Layer I and MPEG-1 Audio Layer III (MP3). While MP3 is much more popular for PC and Internet applications, MP2 remains a dominant standard for audio broadcasting. History of development from MP2 to MP3 MUSICAM MPEG-1 Audio Layer 2 encoding was derived from the MUSICAM (''Masking pattern adapted Universal Subband Integrated Coding And Multiplexing'') audio codec, developed by Centre commun d'études de télévision et télécommunications (CCETT), Philips, and the Institut für Rundfunktechnik (IRT) in 1989 as part of the EUREKA 147 pan-European inter-governmental research and development initiative for the development of a system for the broadcasting of audio and data to fixed, portable or mobile receivers (established in 1987). It began as the Digital Audio Broadcast (DAB) project managed ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polyphase Quadrature Filter
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. These sub-bands are subsampled by a factor of N, so they are critically sampled. An important application of the polyphase filters (of FIR type) concerns the filtering and decimation of large band (and so high sample rate) input signals, e.g. coming from a high rate ADC, which can not be directly processed by an FPGA or in some case by an ASIC either. If the ADC plus FPGA/ASIC interface implements a demultiplexer of the ADC samples in N internal FPGA/ASIC registers, the polyphase filter transforms the decimator FIR filter canonic structure in N parallel branches clocked at 1/N of the ADC clock, allowing digital processing when N=Clock(ADC)/Clock(FPGA). This critical sampling introduces aliasing. Similar to the MDCT time domain alias cancellation the aliasing of polyphase quadrature filters is canceled by neighbouring sub-bands, i. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lossy Compression
In information technology, lossy compression or irreversible compression is the class of data compression methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to reduce data size for storing, handling, and transmitting content. The different versions of the photo of the cat on this page show how higher degrees of approximation create coarser images as more details are removed. This is opposed to lossless data compression (reversible data compression) which does not degrade the data. The amount of data reduction possible using lossy compression is much higher than using lossless techniques. Well-designed lossy compression technology often reduces file sizes significantly before degradation is noticed by the end-user. Even when noticeable by the user, further data reduction may be desirable (e.g., for real-time communication or to reduce transmission times or storage needs). The most widely used lossy compression al ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
The Core Pocket Media Player
The Core Pocket Media Player (TCPMP) is a software media player which operates on portable devices and Windows-based PCs. It is discontinued, but still available from the official mirror site. Supported operating systems include Palm OS, Symbian OS, and Microsoft Windows, CE, and Mobile. It is also available on Microsoft's Zune HD via a hack called Liberate. TCPMP also has hardware accelerated playback for ATI and Intel 2700G mobiles, such as the Tapwave Zodiac and Dell Axim X50v/X51V. Development of the free version of the software was discontinued by CoreCodec in favour of the commercially licensed CorePlayer, though TCPMP is still regarded as one of the more versatile media players for PocketPC and Palm OS mobile devices. History According to the CoreCodec.com website as of September 2002, the development team planned to continue development and releases of the open source version of the player "offsite"; this code would also be incorporated into the commercial player. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
MPEG-1 Audio Layer II
MPEG-1 Audio Layer II or MPEG-2 Audio Layer II (MP2, sometimes incorrectly called Musicam or MUSICAM) is a lossy audio compression format defined by ISO/IEC 11172-3 alongside MPEG-1 Audio Layer I and MPEG-1 Audio Layer III (MP3). While MP3 is much more popular for PC and Internet applications, MP2 remains a dominant standard for audio broadcasting. History of development from MP2 to MP3 MUSICAM MPEG-1 Audio Layer 2 encoding was derived from the MUSICAM (''Masking pattern adapted Universal Subband Integrated Coding And Multiplexing'') audio codec, developed by Centre commun d'études de télévision et télécommunications (CCETT), Philips, and the Institut für Rundfunktechnik (IRT) in 1989 as part of the EUREKA 147 pan-European inter-governmental research and development initiative for the development of a system for the broadcasting of audio and data to fixed, portable or mobile receivers (established in 1987). It began as the Digital Audio Broadcast (DAB) project man ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ogg Vorbis
Vorbis is a free and open-source software project headed by the Xiph.Org Foundation. The project produces an audio coding format and software reference encoder/decoder (codec) for lossy audio compression. Vorbis is most commonly used in conjunction with the Ogg container format and it is therefore often referred to as Ogg Vorbis. Vorbis is a continuation of audio compression development started in 1993 by Chris Montgomery. Intensive development began following a September 1998 letter from the Fraunhofer Society announcing plans to charge licensing fees for the MP3 audio format. The Vorbis project started as part of the Xiphophorus company's Ogg project (also known as OggSquish multimedia project). Chris Montgomery began work on the project and was assisted by a growing number of other developers. They continued refining the source code until the Vorbis file format was frozen for 1.0 in May 2000. Originally licensed as LGPL, in 2001 the Vorbis license was changed to the BSD li ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
ATRAC
Adaptive Transform Acoustic Coding (ATRAC) is a family of proprietary audio compression algorithms developed by Sony. MiniDisc was the first commercial product to incorporate ATRAC in 1992. ATRAC allowed a relatively small disc like MiniDisc to have the same running time as CD while storing audio information with minimal loss in perceptible quality. Improvements to the codec in the form of ATRAC3, ATRAC3plus, and ATRAC Advanced Lossless followed in 1999, 2002, and 2006 respectively. Files in ATRAC3 format originally have the extension, however in most cases the files would be stored in an OpenMG Audio container using the extension . Initially files that were encrypted with OpenMG had the extension, before it was replaced by starting in SonicStage v2.1. Encryption is no longer compulsory as of v3.2. Other MiniDisc manufacturers such as Sharp and Panasonic also implemented their own versions of the ATRAC codec. History ATRAC was developed for Sony's MiniDisc format. ATRAC w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Psychoacoustics
Psychoacoustics is the branch of psychophysics involving the scientific study of sound perception and audiology—how humans perceive various sounds. More specifically, it is the branch of science studying the psychological responses associated with sound (including noise, speech, and music). Psychoacoustics is an interdisciplinary field of many areas, including psychology, acoustics, electronic engineering, physics, biology, physiology, and computer science. Background Hearing is not a purely mechanical phenomenon of wave propagation, but is also a sensory and perceptual event; in other words, when a person hears something, that something arrives at the ear as a mechanical sound wave traveling through the air, but within the ear it is transformed into neural action potentials. The outer hair cells (OHC) of a mammalian cochlea give rise to enhanced sensitivity and better frequency resolution of the mechanical response of the cochlear partition. These nerve pulses then trave ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Double-blind Tests
In a blind or blinded experiment, information which may influence the participants of the experiment is withheld until after the experiment is complete. Good blinding can reduce or eliminate experimental biases that arise from a participants' expectations, observer's effect on the participants, observer bias, confirmation bias, and other sources. A blind can be imposed on any participant of an experiment, including subjects, researchers, technicians, data analysts, and evaluators. In some cases, while blinding would be useful, it is impossible or unethical. For example, it is not possible to blind a patient to their treatment in a physical therapy intervention. A good clinical protocol ensures that blinding is as effective as possible within ethical and practical constraints. During the course of an experiment, a participant becomes unblinded if they deduce or otherwise obtain information that has been masked to them. For example, a patient who experiences a side effect may correc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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