From: Ross L. <ro...@st...> - 2024-07-25 23:06:36
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I'm not sure that's a good idea. I believe better quality settings use more aggressive Huffman encoding to pack the file smaller. That will be the main reason it's taking less time encoding at -q4. -----Original Message----- From: Maik Merten via Lame-dev [mailto:lam...@li...] Sent: Friday, 26 July 2024 3:15 am To: lam...@li... Subject: Re: [Lame-dev] CBR/ABR quality regressions for q0, q1, q2 and q3 Hello, I updated the bug report with, perhaps, a better constructed patch: https://sourceforge.net/p/lame/bugs/516/ This latest patch simply maps the quality levels 0, 1, 2 and 3 to 4, similarly to how the quality-levels are handled for the new VBR mode. Of course, it would be best to find out *why* the settings 0 to 3 don't work well with CBR and ABR and fix *that*, but this is a very non-interfering (I hope) way to fix the symptoms. It even gives a neat speed-boost. Hopefully, any of the LAME developers with commit access might have a look at that trivial patch. Best regards, Maik Am 12.07.24 um 18:57 schrieb Maik Merten: > Hello there, > > it has been observed that with CBR and ABR, perceived audio quality > increases when using faster settings than default. > > A discussion regarding this over at HydrogenAudio: > https://hydrogenaud.io/index.php/topic,126120.0.html > > This is very easily noticeable with very low bitrates, but is also > detectable with the default bitrate of 128 kbps. The discussion thread > on HydrogenAudio includes samples. > > I traced this down to cfg->noise_shaping_amp, which is set to 1 for > -q3/-q2 and is set to 2 for -q1/-q0. Choosing a value of 0 (as for the > faster quality settings) improves perceived audio quality. > > I opened up a bug report a while back over at > https://sourceforge.net/p/lame/bugs/516/ with trivial patches and an > attempt at a theory of why quality might be affected negatively with > noise_shaping_amp being set to 1 or 2. This, however, is merely > speculative, as it's not quite clear to me what settings 1 and 2 are > actually trying to achieve - presumably, those are intended to increase > quality (and perhaps they do in VBR?), but I don't quite understand the > reasoning behind those approaches. > > While setting noise_shaping_amp to 0 is a trivial thing to do, it might > also be (pure speculation, again) that the actual root cause is with the > CBR and ABR encoding loops somehow not interacting properly with > noise_shaping_amp 1/2 and that a "true fix" might involve tinkering with > those encoding loops. > > How would one progress on this issue? With -q3 being the default > setting, rather regrettably CBR and ABR encodings are impacted > negatively by default. > > Another, but most likely minor thing: It appears that noise_shaping_stop > is unused, yet set up by lame_init_qval. I assume this could be removed? > > Best regards, > Maik _______________________________________________ Lame-dev mailing list Lam...@li... https://lists.sourceforge.net/lists/listinfo/lame-dev |