Re: CBR/ABR quality regressions for q0, q1, q2 and q3

I see.  What's slowing down the encoding when using -q0 then?

-----Original Message-----
From: Maik Merten via Lame-dev [mailto:[email protected]] 
Sent: Friday, 26 July 2024 4:07 pm
To: [email protected]
Subject: Re: [Lame-dev] CBR/ABR quality regressions for q0, q1, q2 and q3

Hello Ross,

-q4 already has the full Huffman code search. (-q5 does not)

I'm currently not quite sure any LAME developer with commit access (for 
whatever patch approach) is following this discussion, though.

Best regards,
Maik

Am 26.07.24 um 01:06 schrieb Ross Levis via Lame-dev:
> 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:[email protected]]
> Sent: Friday, 26 July 2024 3:15 am
> To: [email protected]
> 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
> 
> 
> 
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