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Vorbis Bitrate compared to MP3
Frankie
post Mar 2 2006, 00:04
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Today I ripped and converted a CD (Led Zeppelin - IV) to both MP3 (LAME 3.96.1 APE) and Vorbis (aoTuV b4b q6). And I was really surprised to see that the track with the highest bitrate in MP3 (267 kbps) has the lowest bitrate in Vorbis (182 kbps) and the track with the lowest bitrate in MP3 (224 kbps) hast the highest bitrate in Vorbis (207 kbps). So it's exactly vice versa! How can that be? I mean, psycho-acoustic models shouldn't be that different, should they?



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Shade[ST]
post Mar 2 2006, 00:55
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The mp3 format has an issue called sfb21 bloating. Look it up. (google?)
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Frankie
post Mar 2 2006, 07:31
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QUOTE (Shade[ST] @ Mar 1 2006, 03:55 PM)
The mp3 format has an issue called sfb21 bloating.  Look it up. (google?)
*

OK, that maybe explains the overall high bitrate when using LAME for rock/metal, but it doesn't seem to explain why highest/lowest-bitrate is reversed.





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gameplaya15143
post Mar 3 2006, 04:36
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gwen stefani - bubble pop electric.. encoded with vorbis @ q 0 jumps up to ~112kbps in the beginning... so yea.. its just differences in the psy-models (sorry, cant give a more technical answer tongue.gif )


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Vorbis-q0-lowpass99
lame3.93.1-q5-V9-k-nspsytune
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moozooh
post Mar 16 2006, 07:37
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I've found some correlations between Lame and Musepack's psymodels: for the majority of cases, they tend to manage the bitrate almost equally.
If I'll have enough time during the week, I'll post some details.


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HotshotGG
post Mar 16 2006, 08:05
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QUOTE
gwen stefani - bubble pop electric.. encoded with vorbis @ q 0 jumps up to ~112kbps in the beginning... so yea.. its just differences in the psy-models (sorry, cant give a more technical answer tongue.gif )


The way the bitrate allocation scheme works it in Vorbis the higher bitrate flactuation is a result of Vorbis have to allocate more bits to what are called impulse short blocks to deal with transients and other "percussive" noises. It can allocate as many bits as it needs, because it's a true VBR coder. Listen to a track with an accoustic guitar in it or other percussive instruments like castanets, which is also used to fine tune a lot of psychoacoustics model for pre-echo, etc.


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