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opus experimental versions as part of opus-tools, and other questions, just curious
post Feb 3 2013, 01:32
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Hi all,
I've been playing with Opus for a bit and really like it, but I do have some signals that trip it up as high as 128 kbps, and even higher sometimes. I even created a very simple sample which tripped it up at 160 and above, but I will need to do more testing to make sure the codec was to blame. If that indeed is the problem, I will put them here along with ABX so hopefully it can be improved. In fact I am probably violating a rule by saying I can hear these without posting evidence, but again I have to do further testing to make sure this is legitimate.
But first I was going to run these few samples past the experimental builds which seem to try to address these issues. But I don't know where to obtain them. I once found one, but I can't remember the version, or where i got it. I would be looking for the opusenc utility like the one in the command line opus-tools. I really hope these are being made somewhat regularly because I have no clue on how to work with sources.
Also, if these builds really do improve quality, and I think they will, will they begin folding back into the main release like AoTuV did with the official Vorbis years ago?
And another interesting thought. Could the research that went into developing Opus be used to refine a codec like Vorbis which is only for storage? Maybe some new coding strategies based on Celt but something which works well in high delay situations. I know Opus is great for storage as is, and was intended to be so, but if low delay codecs are at so much of a disadvantage, then it would make sense to wonder what something like Opus could do without that restriction. It's probably impractical at least for now but it's an interesting thought.
Thanks for your answers and have a good day!
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post May 9 2013, 11:38
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As nobody more authoritative has replied... No, I don't think it's implemented in the test builds we've seen here.

For limited public testing of experimental builds, such as here, releases are a little less frequent than changes to the git (from which the devs may compile frequently) once a few major changes have been incorporated and are ready to be tested on a range of real world samples and different listeners.

In the recent experimental version thread someone reported that music detection activated only on the third note of a sample and this was because the first two tones were within the lowest frequency bin - a result of Opus's short transform windows thanks to its short frames (20ms), where low frequencies can look a lot like a DC signal. If you take a longer transform window (lasting more than 20ms), the frequency width of each bin is reduced commensurately and that's one way to detect the onset of music consisting of low frequencies but little high-end, though there are other options and I suspect the devs have worked on picking the optimal choice for this application and putting those fixes into the git repository ready for the next release.

Any method I can think of to pick up this corner case pretty much demands more look-ahead, so this fix could only be made in offline mode, not interactive. Any other fixes to problems found in that experimental version will also be addressed in git if possible before a future experimental version is put up incorporating those fixes and asking for further serious testing.
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