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Audio formats (Part.2)

Author MixCorner 4 March 2018, in - Audio - Dossier. | 85 visites pour cet article.

PRELIMINARY

Last time we’ve covered the domain of “Lossy” formats, which present the disadvantage to induce an effect on the audio file’s integrity. For example, if someone makes the conversion from a “.wav” audio file into a MP3 format and the newly created MP3 files back to the “.wav” format…
The file has been changed and doesn’t absolutely correspond to the initial “.wav” format !
Such occurrence doesn’t prevail with the “Lossless”..but obviously Lossless performances have an “additional cost”.

LET’S HAVE A MORE DETAILED LOOK IN IT

“Lossless” formats include algorithms that differ from those used by ”Lossy’s” formats. They are able to compress an audio file but their peculiarity is that uncompressing a file will lead to recover an exact copy of the original one. Thanks to those efficient algorithms!
They are related to audio files and could be compared with the job made to get the .zip format in text files. The ”.zip” compression doesn’t alter-fortunately- the text files which remains absolutely readable.
Then, why not to use this efficient tool?

THE DRAWBACK

The main reason is the “size” of the files generated. MP3 conversion can generate a file that may be reduced up to 8-10 times as regards to the original file while a Codec LossLess is only capable to reach a 50% reduction and in some cases even less.
Knowing that a stereo audio file of one minute length under .wav format weights around 10 Mo, lest see concrete example on how heavy is the final compressed file obtained.

Voici le même fichier dans différents formats
Voici le même fichier dans différents formats

Les variations de taille de fichier selon le format sont énormes

Plus en détails, voici les réglages de compression de chaque Codec:
MP3: (Réglages par défaut)

Réglages pour la compression en MP3
Réglages pour la compression en MP3

Le logiciel utilisé est XLD pour Mac

FLAC: (Réglages par défaut)

Réglages pour la compression en FLAC
Réglages pour la compression en FLAC

Le logiciel utilisé est XLD pour Mac

One may immediately figure out which impact the Codec can have on a given file and understand why the legal downloading platforms offer almost exclusively the MP3 and/or AAC Formats.
This having been said, an additional issue of the Lossless formats is their compatibility. For example, a “Flac” file can’t be managed by either an Iphone…but this holds true too for most of MP3 readers.
Such “formats” are mostly dedicated to selected persons like the audiophiles.

AUDIO LOSSLESS FORMATS

Hereafter is a non exhaustive list:

  • FLAC (.flac) FLAC is obviously the most known and compatible LossLess format ( by the way it is also open source). FLAC represents not only the format but also the Codec it uses.
    Designed already in the years 2000 by Josh Coalson, i twill take a long period of time prior its use. An updated version will even be proposed in 2001.
    In 2003, Josh Coalson claims the integration of FLAC within the project Xiph.org under the sponsoring of the Xiph (Vorbis, Ogg). The adventure lasts until 2013 with a new version 1.3.0. However, it is not used anymore those days.
  • ALAC (.m4a)(Apple Lossless Audio Codec) has been designed by Apple in 2004 to be compatible with their ITunes software and to offers to users the possibility of making copy of their CDs with a high quality. Since 2011, it doesn’t belong to proprietary format, is free of charge and open source.
    ALAC commonly named Apple Lossless may manage up to 8 channels (16/20/24/32 bits) with a sampling frequency able to reach 384 kHz.
    The level of compression is from 40 to 60% depending of the music style compressed. While the extension of the files are identical (.m4a) the files processing has nothing in common.
  • MPEG-4 SLS (.m4a) This format is associated with the very active Fraunhofer foundation together with the Institute for Infocomm Research. The MPEG-4 SLS (MPEG-4 Scale to Lossless) is an extension of the MPEG-4 Audio that has the property to be able of performing adaptive compression in accordance with the “Lossy” specifications.
    The files are in fact converted in LossLess but they can be played by a device able to read the MPEG-4 Audio like an IPod.
    Fraunhofer will commercialize part of that “Standard” under the HD-AAC name. To add a little bit more of confusion, the extension used is also.m4a!
  • Monkey’s Audio (.ape) This format exists since 15 years and still under development by Matthew T. Ashland. Main advantages are a better compression‘s level as compared to most of LossLess formats together with its compatibility Multihreading/multi core.
    However its weakness is that it uses as many processes for “encoding” than for “decoding” which is fully incompatible for portable devices.
    Monkey’s Audio is fully operational under Windows while only the function “decoding” is supported by other platforms.
  • WavPack (.wv) The amazing characteristic of this format is its huge difference in compression efficiency according to the music style. Its range is from 30 to 70 % for actual music styles but it shines the best on music having a large dynamic range such as the Classical Music.
    Creation of hybrid files Lossless/Lossy is possible as the MPEG-4 SLS and WavPack is in open source.
  • Shorten (.shn) Shorten (.shn) is an older format, the final version (3.6.1) having been released in 2007. It can be considered as obsolete while updates of FLAC and WavPack are still under development. However, some times ago, it has been mentioned officially for recording some concerts.
  • WMA Lossless (.wma) Issued in 2003, that format has been designed to archive CDs with compression ratio of 1.7/1 – 3/1.
    Resulting sizes of a compressed CD may vary between 206 to 411Mo (while the size of non compressed CD would be around 650 Mo). Its flow rate being from 470 à 940 kbit/s ( data from Microsoft). WMA Lossless works only under VBR (Variable Bit Rate).
  • ATRAC Advanced Lossless (.aa3) Like MEPG-4SLS and WavPack the current version of ATRAC uses hybrid encoding. File is encoded under ATRA3/ATRAC3plus (corresponding therefore to some data loss). However, it includes a correction flow inserted within the file itself that allows the compatible reader device to select playing with or whithout LossLess. It’s mainly used by PlayStation 3, Game console PSP and Minidiscs.

MixCorner




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