From: Maik M. <mai...@go...> - 2024-07-18 06:00:17
|
Hello Ross, yes, with LAME's current release (and also LAME's SVN), it's easy to come up with samples where -q0 sounds worse than -q4 in CBR and ABR encoding. This is especially apparent with low bitrates, but can also be detected at the default bitrate of 128 kbps. Personally, I haven't had a sample where -q4 sounds worse than -q0 (but plenty where -q0 sounds worse than -q4), which is why I'm confident this is an actual bug, but I certainly recommend giving it a try with your own ears. To easily be able to distinguish the difference, one can experiment with ambitious low-bitrate encoding (assuming test.wav is CD-quality stereo music): lame --resample 44100 --lowpass 16000 -b96 -q0 test.wav q0.mp3 lame --resample 44100 --lowpass 16000 -b96 -q4 test.wav q4.mp3 (these are settings below MP3's comfort level, but one wouldn't expect -q0 to do worse than -q4 nonetheless) Depending on the input, -q0 can collapse into a smeary, metallic mess where -q4 holds up noticeable better. Usually, the lower the bitrate, the more obvious the differences become. Some more discussion and audio samples have been posted over at https://hydrogenaud.io/index.php/topic,126120.0.html Best regards, Maik Am 18.07.24 um 02:59 schrieb Ross Levis via Lame-dev: > I'm not a LAME developer but I am a developer that uses LAME. I'm curious if you are both saying that using -q4 with a CBR encoding > would actually produce better results than -q0? > > -----Original Message----- > From: Maik Merten via Lame-dev [mailto:lam...@li...] > Sent: Thursday, 18 July 2024 4:40 am > To: lam...@li... > Subject: Re: [Lame-dev] CBR/ABR quality regressions for q0, q1, q2 and q3 > > Hello again, > > the regression was introduced with > > https://sourceforge.net/p/lame/svn/6147/ > > With this commit, CBR and ABR encoding was switched over the the newer > VBR-psy-model. > > Other than that, the encoding loops for CBR and ABR apparently were not > changed. With the older psy-model (up to revision 6146), > noise_shaping_amp being set to 1 or 2 does not appear to have a > detrimental effect. This demonstrates IMO that noise_shaping_amp is not > in principle incompatible with CBR/ABR, but presumably something went > awry when switching over to the VBR-psy-model. > > Disabling noise_shaping_amp for the affected modes still seems to be the > easy workaround, but if it's possible to have noise_shaping_amp work as > intended, that'd of course be very neat. > > > 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 > > > > > _______________________________________________ > Lame-dev mailing list > Lam...@li... > https://lists.sourceforge.net/lists/listinfo/lame-dev |