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Experimental release of Ghost/CELT 0.0.1
jmvalin
post Dec 9 2007, 11:53
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Xiph.org Speex developer


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Posts: 479
Joined: 21-August 02
Member No.: 3134



I've just made the first public release of some new *experimental* codec work I've been doing (part of the vague Ghost project) with help from Monty and Timothy. This is mainly intended for developers with DSP knowledge, not for doing anything useful with it (but it does encode and decode already). Also, the main idea is *not* to replace either Speex or Vorbis, but to code audio with really low latency -- currently 8 ms.

This is still very experimental and everything is still likely to change, including the exact goals. The algorithm is called (temporary name) Code-Excited Lapped Transform (CELT) and the main ideas are:
- Using an MDCT on very short frames
- Dividing into 15 bands and transmitting the energy for each band
- Using a pitch predictor (good for speech, but helps for music as well).
- The rest is coded using a unit-pulse codebook.
At this point, I'm still trying to figure out how to fit psychoacoustics into this.

CELT is based on a paper I submitted to ICASSP and which I'm hoping will be accepted so I can make it available to everyone. The only difference is that the ICASSP paper was based on the FFT (non critically sampled), whereas this version is based on the MDCT. One part that is already published though is Tim's explanation of the pulse codebook encoding.

The full source for CELT is available at: http://downloads.us.xiph.org/releases/celt/celt-0.0.1.tar.gz or through git at http://git.xiph.org/celt.git

I've put some music samples at 56 kbps CBR at http://people.xiph.org/~jm/comp_celt58cbr.wav with the original at http://people.xiph.org/~jm/comp44.wav . As you can hear, it definitely doesn't suck as much as Speex on music, but there's still room for improvement.

I'm open to interesting ideas, but don't bother complaining if it doesn't work or if it explodes in your face :-) Oh, and don't expect a final codec any time soon.

Have fun!
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Saoshyant
post Mar 7 2008, 04:08
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The recent aoTuV tunings have not yet been merged with the official tree because it's no easy matter. It requires a lot of testing and studying both the code and the results. On a recent talk, Monty mentioned it would be a work of two full-time weeks, which surprised me as I had no idea he would be so through. However, he also mentioned it would be something that would be likely done this year, which I suppose is good news for all those waiting for the merge.

The Xiph people are doing some good work. Put some faith in them and keep spreading those files. And if you want to take a more direct approach to help out, join in and contribute somehow. There will always be something you (and anyone else) can do to speed up progress.


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Join //spreadopenmedia.org to promote Vorbis, FLAC, Speex, etc
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Posts in this topic
- jmvalin   Experimental release of Ghost/CELT 0.0.1   Dec 9 2007, 11:53
- - radorn   So this codec is not intended to eventually replac...   Dec 20 2007, 14:36
|- - Benjamin Lebsanft   QUOTE (radorn @ Dec 20 2007, 14:36) So th...   Dec 20 2007, 16:04
|- - jmvalin   QUOTE (radorn @ Dec 20 2007, 22:36) So th...   Dec 20 2007, 21:40
|- - SebastianG   QUOTE (jmvalin @ Dec 20 2007, 21:40) For ...   Dec 21 2007, 20:51
|- - jmvalin   QUOTE (SebastianG @ Dec 22 2007, 04:51) W...   Dec 22 2007, 03:57
|- - SebastianG   QUOTE (jmvalin @ Dec 22 2007, 03:57) In t...   Dec 23 2007, 12:17
|- - jmvalin   QUOTE (SebastianG @ Dec 23 2007, 20:17) N...   Dec 23 2007, 13:22
|- - jmvalin   Here's some information on the pitch predictor...   Dec 26 2007, 13:15
|- - SebastianG   QUOTE (jmvalin @ Dec 26 2007, 13:15) Here...   Jan 2 2008, 18:01
- - radorn   Sorry for the misunderstanding and thank you both ...   Dec 21 2007, 11:27
- - Kef   QUOTE (jmvalin @ Dec 9 2007, 12:53) I...   Jan 19 2008, 13:34
|- - jmvalin   QUOTE (Kef @ Jan 19 2008, 21:34) Now, I k...   Feb 3 2008, 11:57
|- - johnsonlam   QUOTE (jmvalin @ Feb 3 2008, 18:57) Keep ...   Feb 21 2008, 06:18
|- - jmvalin   QUOTE (johnsonlam @ Feb 21 2008, 14:18) A...   Feb 22 2008, 03:16
- - Nicos   I absolutetly agree with what u stated above Kef. ...   Jan 22 2008, 12:23
- - Brent   A sense of "progress" I suppose. Every n...   Feb 22 2008, 23:38
|- - jmvalin   QUOTE (Brent @ Feb 23 2008, 07:38) A sens...   Feb 24 2008, 10:53
- - Saoshyant   Xiph also made an announcement of everything that ...   Mar 6 2008, 03:16
- - Bourne   -   Mar 6 2008, 04:09
- - Saoshyant   The recent aoTuV tunings have not yet been merged ...   Mar 7 2008, 04:08


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