In case people on the list don't know it, A Vorbis tester (who's email I've lost! If you're on the list, speak up!) is maintaining a vorbis audio quality test page: http://hem.passagen.se/ingets1/vorbis.htm He's doing us the great service of hunting down samples that break Vorbis (so we don't have to :-) In any case, it turns out that the trumpets in the dr4 sample are reliably mistriggering the preecho detector (which implies either a large bug in the detector, or general borkkenness which must be fixed). The artifacts in the sample are due entirely to Vorbis trying to encode the trumpets entirely in short blocks (which will suck for strongly periodic/harmonic waveforms, as produced by brass instruments). Just a heads up; if someone else runs across this artifact (it manifests as 'wayyy to much noise/rasp'), you know that I knwo about it. Monty --- >8 ---- List archives: http://www.xiph.org/archives/ Ogg project homepage: http://www.xiph.org/ogg/
> In any case, it turns out that the trumpets in the dr4 sample are reliably > mistriggering the preecho detector (which implies either a large bug in the > detector, or general borkkenness which must be fixed). The artifacts in the > sample are due entirely to Vorbis trying to encode the trumpets entirely in > short blocks (which will suck for strongly periodic/harmonic waveforms, as > produced by brass instruments).This also means that Vorbis is currently wasting bits and hurting sound quality at the same time... The *good* news is that fixing the problem will silmultaneously make things smaller and higher quality. The sample in question codes perfectly at 98kbps when I turn off short blocks... Monty --- >8 ---- List archives: http://www.xiph.org/archives/ Ogg project homepage: http://www.xiph.org/ogg/
On Fri, 16 Jun 2000, Monty wrote:> In case people on the list don't know it, A Vorbis tester (who's email I've > lost! If you're on the list, speak up!) is maintaining a vorbis audio quality > test page: > > http://hem.passagen.se/ingets1/vorbis.htm > > He's doing us the great service of hunting down samples that break Vorbis (so > we don't have to :-) > > In any case, it turns out that the trumpets in the dr4 sample are reliably mistriggering the preecho detector (which implies either a large bug in the detector, or general borkkenness which must be fixed). The artifacts in the sample are due entirely to Vorbis trying to encode the trumpets entirely in short blocks (which will suck for strongly periodic/harmonic waveforms, as produced by brass instruments). > > Just a heads up; if someone else runs across this artifact (it manifests as > 'wayyy to much noise/rasp'), you know that I knwo about it.By the way, do we use the LSP hysterisis on short as well as long blocks? If not, that might improve the situation.. (Actually, looking breifly at the hysterisis code, we *are* keeping the states seperate between short and long right?) I ask because it sounds like bad LSP fit due to the shortblocks not being trained well for strongly tonal signals. Another hysterisis suggestion: If some criteria is not met (like the last short block was more then 3 blocks ago, or there is some sort of other detectable change) then perform a brute force lookup. The slowdown from doing that every block would be too much, but perhaps, the slowdown from doing it every once in a while might be acceptible.. It might improve quality by giving a better inital match for the hysterisis.. --- >8 ---- List archives: http://www.xiph.org/archives/ Ogg project homepage: http://www.xiph.org/ogg/
Monty schrieb am Fre, 16 Jun 2000:> In case people on the list don't know it, A Vorbis tester (who's email I've > lost! If you're on the list, speak up!) is maintaining a vorbis audio quality > test page: > > http://hem.passagen.se/ingets1/vorbis.htm > > He's doing us the great service of hunting down samples that break Vorbis (so > we don't have to :-) > > In any case, it turns out that the trumpets in the dr4 sample are reliably mistriggering the preecho detector (which implies either a large bug in the detector, or general borkkenness which must be fixed). The artifacts in the sample are due entirely to Vorbis trying to encode the trumpets entirely in short blocks (which will suck for strongly periodic/harmonic waveforms, as produced by brass instruments). > > Just a heads up; if someone else runs across this artifact (it manifests as > 'wayyy to much noise/rasp'), you know that I knwo about it. > > Montyome files vorbizing doesn't do well, hmm I think you are aware of these testcases already: 60.wav, frer07_1.wav very audible distortions applaud.wav clipping problems in nearly all frames fatboy.wav sounds bad as with most encoders gspi35_2.wav doesn't sound right imho frer* and gspi* are SQAM tracks: http://sound.media.mit.edu/mpeg4/audio/sqam the rest you can find at sulaco.org Ciao Robert --- >8 ---- List archives: http://www.xiph.org/archives/ Ogg project homepage: http://www.xiph.org/ogg/