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opus experimental versions as part of opus-tools, and other questions, just curious
raygrote
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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raygrote
post Feb 4 2013, 22:52
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Okay will do. It seems that the alpha works better for the tonal samples, and is using a more unconstrained VBR? Because on the samples I tested which had problems with 1.0.2, the alpha 1.1 did much better with a substantial increase in bitrate. The test I did was targetted at 64kbps, and 1.0.2 gave a bitrate of 65, while 1.1 gave one of around 86 I think. If I forced CBR on both versions, 1.0.2 had more distortion in the low end and 1.1 fixed that, but introduced a bit more on the mids and highs which I find more agreeable, since it still beats the griddy sound of SBR in my opinion. I have yet to find a sample that really trips the alpha at a reasonable bitrate like the previous version did, but I will be sure to let you know if I do.
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jmvalin
post Feb 5 2013, 00:16
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QUOTE (raygrote @ Feb 4 2013, 16:52) *
Okay will do. It seems that the alpha works better for the tonal samples, and is using a more unconstrained VBR? Because on the samples I tested which had problems with 1.0.2, the alpha 1.1 did much better with a substantial increase in bitrate. The test I did was targetted at 64kbps, and 1.0.2 gave a bitrate of 65, while 1.1 gave one of around 86 I think. If I forced CBR on both versions, 1.0.2 had more distortion in the low end and 1.1 fixed that, but introduced a bit more on the mids and highs which I find more agreeable, since it still beats the griddy sound of SBR in my opinion. I have yet to find a sample that really trips the alpha at a reasonable bitrate like the previous version did, but I will be sure to let you know if I do.


Keep in mind that on average, 1.1 uses the same bit-rate as 1.0.2. On hard samples it'll use a higher rate, while on easier samples, it'll go below 64 kb/s. Also, if you don't want these large variations, you can always enable "constrained VBR", which is about equivalent to what MPEG codecs call CBR (they use a bit reservoir to pretend they're CBR).
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