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samples where aps or ape has a problem
2Bdecided
post Mar 24 2003, 17:01
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I'm sure this has been asked before, but I can't find it, and it's not in the FAQ (it should be - please!)

On which samples is --alt-preset extreme audibly better than --alt-preset standard.
On which samples is --alt-preset insane audibly better than --alt-preset extreme.
On which samples is --alt-preset insane not transparent?

Cheers,
David.
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JohnV
post Apr 4 2003, 12:43
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QUOTE (2Bdecided @ Apr 4 2003 - 01:11 PM)
You and JohnV have removed any serious quality worries, but there was also the issue of bloat. I've read that -Z may increase the bitrate. Maybe I don't have the right test samples, but this is barely happening here - it's a 1kbps increase.

Can someone who has a CD which produces a low bitrate using aps try encoding it again with aps -Z please?


DickD - yes! Will someone else listen to aps -Z please? I'm a good listener, but I'm in a noisy environment and I can't hear above 16kHz - so other people really need to check what I'm saying! It doesn't have to be badvilbel - there's plenty of other fun samples - or just grab a CD at random.

Yes, using aps/ape -Z increases bitrate but not always. Also one have to understand that there are only some positions on a track where noise-shaping 1 and noise-shaping 2 can sound different, the positions where one or both noise shaping types use scalefactor_scale.

Noise Shaping 1 (APS/APE -Z):
When Lame notices that all scalefactors are even numbered, it halves the values thus saving some bits in coding. This is quality wise "lossless" and is no different outcome than using no scalefac_scale at all (except for the bit saving).

So when Noise Shaping type 1 is used, only lossless bitrate saving happens in certain places. (You can see with EncSpot how many percent of the track is encoded using scalefac_scale).


Noise Shaping 2:
Noise Shaping 2 adds another trick for bitrate saving. When the encoder decides to use scalefac_scale (not necessarely in same places as with NS1), the scalefactor values are doubled. Since scalefactors are used to control the reduction of quantization stepsizes (which control how much noise per SFB is present), the dynamics is larger for the stepsize adjustment. It can go more closer to the "edge" of allowed noise, which of course saves bits.

With Noise Shaping 2, Lame should use scalefac_scale only when it's "safe". Obviously this is not always succeeding, and NS2 scalefac_scale can introduce even quite bad audible distortion sometimes, especially when using vbr-old nspsytune. The masking threshold/allowed noise is not perfect because of the imperfect psychoacoustics, and sometimes it fails when it has the chance to go more closer to the edge. I'd think with better psychoacoustics NS2 would work ok.

Now because of code level tweaking, APS/APE use less often Noise Shaping 2 than without code-level tweaking, but it's still not enough to be totally "safe".

IMO NS2, because it's not safe, is not the right type for VBR coding. But CBR acts differently and low bitrate CBR can gain quality from the bitrate savings given by NS2 scalefac_scaling.


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Juha Laaksonheimo
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Posts in this topic
- 2Bdecided   samples where aps or ape has a problem   Mar 24 2003, 17:01
- - Wombat   There are some, http://www.hydrogenaudio.org/foru...   Mar 24 2003, 18:40
- - Pio2001   QUOTE (2Bdecided @ Mar 24 2003 - 07:01 PM)On ...   Mar 24 2003, 22:11
- - KikeG   For me, the trumpets.wav sample sounds much more t...   Mar 24 2003, 23:12
- - 2Bdecided   Thank you all for your responses. I went hunting a...   Mar 25 2003, 17:25
- - Pio2001   QUOTE (2Bdecided @ Mar 25 2003 - 07:25 PM)bad...   Mar 25 2003, 20:50
- - guruboolez   --alt-preset VBR are suffering with harpsichord. E...   Mar 25 2003, 21:11
- - 2Bdecided   guruboolez - thank you - you're right! W...   Mar 26 2003, 11:58
- - 2Bdecided   QUOTE (Pio2001 @ Mar 25 2003 - 07:50 PM)The p...   Mar 26 2003, 11:59
- - guruboolez   · Jump is a song from Van Halen (1984 album, but n...   Mar 26 2003, 12:03
- - 2Bdecided   Reading about the 3.94 alphas, I followed this sug...   Mar 26 2003, 16:57
- - 2Bdecided   At the risk of being a saddo who just bumps his ow...   Mar 27 2003, 11:10
- - KikeG   QUOTE (guruboolez @ Mar 25 2003 - 09:11 PM)In...   Mar 27 2003, 11:56
- - Dibrom   QUOTE (2Bdecided @ Mar 25 2003 - 09:25 AM)P.S...   Mar 27 2003, 12:02
- - Dibrom   QUOTE (2Bdecided @ Mar 26 2003 - 08:57 AM)aps...   Mar 27 2003, 12:07
- - 2Bdecided   Thank you.   Mar 27 2003, 13:25
- - 2Bdecided   To settle aps -Z vs ape -Z vs api in my own mind, ...   Mar 27 2003, 14:01
- - 2Bdecided   ?   Mar 28 2003, 11:27
- - CiTay   Hmm, --aps -Z files aren't really that much bi...   Mar 28 2003, 12:40
- - 2Bdecided   ? Sorry to bump again, but it's kind of impor...   Mar 31 2003, 11:16
- - DickD   I was searching for info on how -Z worked and foun...   Mar 31 2003, 17:14
- - KikeG   IIRC, JohnV said that there's no problem in us...   Apr 1 2003, 10:05
- - 2Bdecided   JohnV did say exactly that, but Dibrom said ...   Apr 1 2003, 10:24
- - 2Bdecided   ? With the many tests samples I've been try...   Apr 3 2003, 15:52
- - JohnV   It has been said many times that Gpsycho has often...   Apr 3 2003, 17:57
- - Dibrom   QUOTE (2Bdecided @ Apr 1 2003 - 02:24 AM)So m...   Apr 3 2003, 18:17
- - DickD   Just guessing (sorry!) but perhaps -Z could ma...   Apr 3 2003, 20:15
- - 2Bdecided   QUOTE (JohnV @ Apr 3 2003 - 04:57 PM)It has b...   Apr 4 2003, 10:53
- - 2Bdecided   QUOTE (Dibrom @ Apr 3 2003 - 05:17 PM)The poi...   Apr 4 2003, 11:11
- - Gabriel   David, would you try adding --athtype 0 to preset ...   Apr 4 2003, 11:20
- - Wombat   I use aps -Z for a long time now. I donīt encode m...   Apr 4 2003, 11:27
- - JohnV   QUOTE (2Bdecided @ Apr 4 2003 - 01:11 PM)You ...   Apr 4 2003, 12:43
- - CiTay   Okay, i changed the List of recommended LAME setti...   Apr 4 2003, 15:16
- - 2Bdecided   QUOTE (Gabriel @ Apr 4 2003 - 10:20 AM)David,...   Apr 4 2003, 16:25
- - 2Bdecided   JohnV - thanks for that long explanation. It would...   Apr 4 2003, 16:31
- - ff123   2BDecided, Thanks for that list of samples. I...   Apr 4 2003, 16:50
- - user   --alt-preset fast standard / extreme ? dev0: ...   Apr 11 2003, 14:02
- - Frank Klemm   QUOTE (JohnV @ Apr 4 2003 - 01:43 PM)Yes, usi...   Apr 11 2003, 15:41
- - 2Bdecided   QUOTE (user @ Apr 11 2003 - 01:02 PM)--alt-pr...   Apr 11 2003, 16:30


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