Evolution of CELT

[jmvalin]

I've been doing some tuning of CELT over the past few days and thought it would be a interesting to compare how the quality of CELT has evolved over the coarse of its development. It's easy to lose track when each change you made provides only a tiny improvement. Using this stereo reference file, I've tried encoding with a few different versions. Even though I don't normally recommend using that bit-rate for stereo, I've used 40 kb/s for the comparison because it makes the artefacts (and thus the differences) more obvious. A bit more than two years ago, this is what CELT 0.3.2 sounded like at 40 kb/s. Then there was version 0.5.2 that improved, with the latest version, 0.8.1. And now, here's what in the current git to be released as 0.9.

OK, I know the quality isn't that good at such a low rate, so here's a slightly higher bit-rate. This is current git at 64 kb/s, compared to G.719 at the same rate. I'm curious to hear comments about how CELT does compared to G.719 because we haven't done any formal comparison yet on music.

Even at 64 kb/s, the artefacts are generally audible, even though they're usually no longer annoying. They start being less audible at 80 kb/s, as you can see, and then the quality continues going up all the way to 256 kb/s or even higher.

Comments

Thanks!

[fwaggle.livejournal.com]

I came here via a Buzz post from Mumble developer dD0T, and I just wanted to say thanks for all the hard work you guys put into CELT/Speex. Mumble sounds fantastic because of the CELT codec and the Speex filtering goodness.

The sound-bytes are really interesting - the difference between 0.3.2 and 0.9 at 40kbps is pretty startling, particularly in the vocals at the end of the clip. I don't think Mumble started with CELT quite so early, IIRC it was around 0.6 or so... and if I'm not mistaken it's typically ran at about 40kbps mono, but I still feel like it's gotten a good bit better in just the time I've been playing with it.

So thanks again for all your hard work. :D