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Audio compression is a form of data compression designed to reduce the size of audio data files. Audio compression algorithms are typically referred to as audio codecs. As with other specific forms of data compression, there exist many " lossless" and " lossy" algorithms to achieve the compression effect.
Compared with image compression, lossless compression algorithms are not nearly as widely used in audio compression. The primary users of lossless compression are audio engineers and those consumers who disdain the quality loss from lossy compression techniques such as Vorbis and MP3.
First, the vast majority of sound recordings are natural sounds, recorded from the real world, and such data doesn't compress well. In a similar manner, photos compress less efficiently with lossless methods than computer-generated images do. But worse, even computer generated sounds can contain very complicated waveforms that present a challenge to many compression algorithms. This is due to the nature of audio waveforms, which are generally difficult to simplify without a (necessarily lossy) conversion to frequency information, as performed by the human ear.
The second reason is that values of audio samples change very quickly, so generic data compression algorithms don't work well for audio, and strings of consecutive bytes don't generally appear very often. However, convolution with the filter [-1 1] (that is, taking the first difference) tends to slightly whiten ( decorrelate , make flat) the spectrum, thereby allowing traditional lossless compression at the encoder to do its job; integration at the decoder restores the original signal. More advanced codecs such as Shorten ( SHNSHN Shorten is a file format used to losslessly compress CD-quality audio files (44. 1 kHz 16-bit stereo PCM). It is similar to ZIP, RAR, and Stuffit but is meant for audio as traditional compression formats do not work well on audio data. The Shorten com), FLACFLAC stands for Free Lossless Audio Codec . FLAC is an audio compression codec that is lossless. Unlike lossy codecs such as MP3 and Vorbis, it does not remove any information from the audio stream. On January 29th, 2003, Xiphophorus (now called the Xiph. and TTATrue Audio (abbreviated TTA is a free, simple real-time lossless audio encoder/decoder, based on adaptive prognostic filters which has shown the same or the better results comparing to majority of modern analogs. TTA Compressor Down to 30% lossless audio uses linear predictionLinear prediction is a mathematical operation where future values of a digital signal are estimated as a linear function of previous samples. In digital signal processing linear prediction is often called linear predictive coding (LPC) and can thus be vie to estimateLinear models Parameter Estimation Deterministic parameters Least-squares (batch and recursive processing) Best linear unbiased estimation (BLUE) Maximum likelihood Random parameters Mean-squared Maximum a posteriori BLUE Weighted least squares State esti the spectrum of the signal. At the encoder, the estimator's inverse is used to whiten the signal by removing spectral peaks while the estimator is used to reconstruct the original signal at the decoder.
Some examples of popular lossless audio codecs:
Lossless audio codecs have no quality issues, so the usabilty can be estimated by
See a comparison at [1] and a graph at [2]
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