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Developed by Xiph.Org Foundation
Type of format Audio
Contained by Ogg
Standard(s) Documentation
Developer(s) Foundation, Jean-Marc Valin
Preview release 0.7.0 / 2009-10-26; 2 months ago
Operating system Cross-platform
Type Audio codec, reference implementation
License 3-clause BSD

CELT (Constrained Energy Lapped Transform) is an open, royalty-free audio compression format and a free software codec for use in low-latency audio communication. It's a lossy codec, meaning quality is permanently degraded to reduce file size.

CELT is meant to bridge the gap between Vorbis and Speex for applications where both high quality audio and low delay are desired.[1] It is suitable to carry both speech and music. It borrows ideas from CELP codec, but avoids some of its limitations by working only with a frequency of a sound.[1]

In December 2007, a first development version of CELT was published.[2] The latest version of CELT is 0.7.0, released on October 26, 2009.[3]

On July 13, 2009 CELT Codec has been submitted as an IETF draft.[4][5] In May 2009, a draft of RTP payload format for the CELT Codec was published.[6]


Technical details

CELT can use sampling rates from 32 kHz to 48 kHz and above, adaptive bit-rate from 32 kbit/s to 128 kbit/s per channel and above. CELT supports mono and stereo and it is applicable to both speech and music. It uses ultra-low algorithmic delay (as low as 2 ms; scalable, typically from 3 to 9 ms). There are no known intellectual property issues and it is free software/open-source.[4][1]


In January 2009 support for CELT was added to the Ekiga[7] and FreeSWITCH[8] VOIP programs.

CELT is also supported or used by[9]:

See also

External links


  1. ^ a b c Xiph.Org The CELT ultra low-delay audio codec - home page, Retrieved 2009-09-01
  2. ^ Xiph.Org (2007-12-08) CELT releases - celt-0.0.1.tar.gz, Retrieved 2009-09-01
  3. ^ Xiph.Org CELT News, Retrieved 2009-11-14
  4. ^ a b CELT IETF draft
  5. ^ IETF - AVT Working Group (2009-07-04) Constrained-Energy Lapped Transform (CELT) Codec, Retrieved 2009-09-01
  6. ^ IETF - AVT Working Group (2009-05-08) RTP Payload Format for the CELT Codec, Retrieved 2009-09-01
  7. ^ Ekiga 3.1.0 available
  8. ^ FreeSWITCH: New Release For The New Year
  9. ^ Software that uses or supports CELT

Simple English

The Celts were a large group of tribes in Europe that first appeared in the Early Iron Age, around 1200 B.C. in Austria. They came from from the Hallstatt and La Tène cultures. Their culture and genes spread through much of Europe, and by the time the Greeks and later the Romans were starting, most of Britain, Ireland, France, Spain, and Central Europe were mostly Celtic. Celtic tribes could be very different from each other. The Celts in Britain, Ireland and other small islands generally followed a polytheistic religion. Their priests were called druids, who had a large amount of power in their society.

The walls of the houses were made of wood however when there was not enough trees to complete all the houses and keep lots of shade they used stone. They had thatched roofs. When you entered the house there would be only one room where the family would eat, sleep, cook and talk.In the centre of the room would be a fire.

The warriors would often paint themselves and try to scare their enemies by charging at them naked and shouting. They also had their own type of sword that was really good at smashing things. The Romans were able to defeat most of them, except for Ireland, Scotland and the islands. The Celts in the other Celtic areas would rebel occasionally. When the Roman Empire fell, a lot of old Celtic land ended up ruled by the invading Germanic peoples. This is why England and France are not seen as Celtic, they became Germanic.

The Celts spoke Celtic languages. Today, the Celtic languages that remain are the Breton, Cornish, Welsh, Manx, Scottish, Irish and Gaelic languages.

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