* act-ACT is a lossy ADPCM 8 kbit / s compressed audio format recorded by most Chinese MP3 and MP4 players with a recording function, and voice recorders

* mpc-Musepack or MPC ( formerly known as MPEGplus, MPEG + or MP +) is an open source lossy audio codec, specifically optimized for transparent compression of stereo audio at bitrates of 160 – 180 kbit / s.

Lossless audio compression produces a representation of digital data that decompresses to an exact digital duplicate of the original audio stream, unlike playback from lossy compression techniques such as Vorbis and MP3.

Some audio formats feature a combination of a lossy format and a lossless correction ; this allows stripping the correction to easily obtain a lossy file.

The innovation of lossy audio compression was to use psychoacoustics to recognize that not all data in an audio stream can be perceived by the human auditory system.

Due to the nature of lossy algorithms, audio quality suffers when a file is decompressed and recompressed ( digital generation loss ).

This makes lossy compression unsuitable for storing the intermediate results in professional audio engineering applications, such as sound editing and multitrack recording.

In order to determine what information in an audio signal is perceptually irrelevant, most lossy compression algorithms use transforms such as the modified discrete cosine transform ( MDCT ) to convert time domain sampled waveforms into a transform domain.

In contrast, lossy compression ( for example JPEG, or MP3 ) can achieve much higher compression ratios at the cost of a decrease in quality, as visual or audio compression artifacts from loss of important information are introduced.

While data reduction ( compression, be it lossy or lossless ) is a main goal of transform coding, it also allows other goals: one may represent data more accurately for the original amount of space – for example, in principle, if one starts with an analog or high-resolution digital master, an MP3 file of a given size should provide a better representation than a raw uncompressed audio in WAV or AIFF file of the same size.

The compression ratio ( that is, the size of the compressed file compared to that of the uncompressed file ) of lossy video codecs is nearly always far superior to that of the audio and still-image equivalents.

Some audio formats feature a combination of a lossy format and a lossless correction which when combined reproduce the original signal ; the correction can be stripped, leaving a smaller, lossily compressed, file.

* Lossy audio formats, comparing the speed and compression strength of five lossy audio formats.

* Data compression basics, including chapters on lossy compression of images, audio and video.

It is also often used as a component within lossy data compression technologies ( e. g. lossless mid / side joint stereo preprocessing by the LAME MP3 encoder and other lossy audio encoders ).

Lossless audio formats are most often used for archiving or production purposes, with smaller lossy audio files being typically used on portable players and in other cases where storage space is limited and / or exact replication of the audio is unnecessary.

* Formats with lossy compression, such as MP3, Vorbis, Musepack, AAC, ATRAC and Windows Media Audio Lossy ( WMA lossy )).

* Lossy codecs: Many of the more popular codecs in the software world are lossy, meaning that they reduce quality by some amount in order to achieve compression.

The design of data compression schemes involve trade-offs among various factors, including the degree of compression, the amount of distortion introduced ( e. g., when using lossy data compression ), and the computational resources required to compress and uncompress the data.

Generally, lossy data compression schemes are guided by research on how people perceive the data in question.

Similarly, DVDs use the lossy MPEG-2 Video codec for video compression.

The theoretical background of compression is provided by information theory ( which is closely related to algorithmic information theory ) for lossless compression, and by rate – distortion theory for lossy compression.

In both lossy and lossless compression, information redundancy is reduced, using methods such as coding, pattern recognition and linear prediction to reduce the amount of information used to represent the uncompressed data.

Most lossy compression reduces perceptual redundancy by first identifying sounds which are considered perceptually irrelevant, that is, sounds that are very hard to hear.

The majority of video compression algorithms use lossy compression.

As in all lossy compression, there is a tradeoff between video quality, cost of processing the compression and decompression, and system requirements.

Some of these methods are inherently lossy while others may preserve all relevant information from the original, uncompressed video.

The advantage of lossy methods over lossless methods is that in some cases a lossy method can produce a much smaller compressed file than any lossless method, while still meeting the requirements of the application.

Some image file formats, like PNG or GIF, use only lossless compression, while others like TIFF and MNG may use either lossless or lossy methods.

It describes a combination of lossy video compression and lossy audio data compression methods which permit storage and transmission of movies using currently available storage media and transmission bandwidth.

This is because lossy compression methods, especially when used at low bit rates, introduce compression artifacts.

DCTs are important to numerous applications in science and engineering, from lossy compression of audio ( e. g. MP3 ) and images ( e. g. JPEG ) ( where small high-frequency components can be discarded ), to spectral methods for the numerical solution of partial differential equations.

Monkey's Audio does not discard data during the process of encoding, unlike lossy compression methods such as AAC, MP3, Vorbis and Musepack.

Rate – distortion theory gives an analytical expression for how much compression can be achieved using lossy compression methods.

For example, in the study of digital signal processing psychophysics has informed the development of models and methods of lossy compression.

Digital cinema cameras rarely use only lossless compression methods, because much higher compression ratios ( lower data rates ) can be achieved with lossy compression.

In data compression and psychoacoustics, transparency is the ideal result of lossy data compression.

The fact that the lossy spectrograms are different from the uncompressed one indicates that they are in fact lossy, but nothing can be assumed about the effect of the changes on perceived quality.

Other types of lossy compressors, such as the linear predictive coding ( LPC ) used with speech, are source-based coders.

Information-theoretical foundations for lossy data compression are provided by rate-distortion theory.

There are two basic lossy compression schemes:

* In lossy transform codecs, samples of picture or sound are taken, chopped into small segments, transformed into a new basis space, and quantized.

This is because these types of data are intended for human interpretation where the mind can easily " fill in the blanks " or see past very minor errors or inconsistencies – ideally lossy compression is transparent ( imperceptible ), which can be verified via an ABX test.

Flaws caused by lossy compression that are noticeable to the human eye or ear are known as compression artifacts.

Many media transforms, such as Gaussian blur, are, like lossy compression, irreversible: the original signal cannot be reconstructed from the transformed signal.

Parametric and lossy ' instantaneous ' ( i. e. electronic ) nonlinear optical phenomena, in which the optical fields are not too large, can be described by a Taylor series expansion of the dielectric Polarization density ( dipole moment per unit volume ) P ( t ) at time t in terms of the electrical field E ( t ):

More frequently, the smaller file sizes of compressed but lossy formats such as MP3 are used to store and transfer audio.

The latest versions of Sony's ATRAC are ATRAC3 and ATRAC3plus, both of which are true lossy compression schemes and both require decompression on replay.