On Wed, Jun 14, 2000 at 11:45:46AM -0600, Mark Taylor wrote:
> > Pierre Hugonnet wrote:
> > Isn't this "Safe VBR" (let's say with 128kbs as a base bitrate)
> > equivalent to a classical VBR with a minimum bitrate: lame -v -b 128
>
> The is one key difference: safe VBR mode chooses the total number of
> bits to use before *any* quantization occurs, based on a simple
> formula (also used by the CBR algorithm). The psycho acoustics are
> only used in allocating the bits among the frequency bands.
>
> The other VBR modes decide on the total number of bits to use based
> soley on how the quantization errors compare to the psycho acoustic
> masking. Ideally, this is a better way to do things, if your psycho
> acoustic model was perfect.
>
> But the psycho acoustic model in LAME far from perfect, and trusting
> it as much as VBR does can lead to mistakes: A good example of this is
> "vbrtest.wav", which was just added to
> www.sulaco.org/mp3/gpsycho/quality.html
Wow, that really _is_ hideous! Even worse than a "twangy" guitar sample
I found the other day.
That made me curious so I decided to do some quick comparisons. Here's
some frivolous data on various encodings of "vbrtest.wav":
Avg.
Encoder options: bitrate Totally subjective comments
----------------------------------------------------------------------
lame -v 111 Warble city! 31% of frames at 80 kbps
lame -h 128 ;-) Sounds great!
lame -h --abr 128 130 ABR indistinguishable from CBR
xingmp3enc -V50 140 Sounds very good, but not "bright"
Normally "lame -v" will produce files of higher average bitrates than
"lame -h --abr 128" or "xingmp3enc -V50". Just how common is this kind
of audio signal (he asks, shuddering)?
I'm really curious about the Xing encoder's bit allocation scheme.
Although their encoder gets a little "dirty" at the low and high end,
they seem to really understand VBR. What are they doing right?
Maybe "unsafe" VBR in LAME should strive to be more like the Xing
results (without the distortion, of course) than like "safe" VBR.
Also, I'm impressed with how good LAME is with a plain ol' 128 kbps CBR
encoding. That kind of compression is the whole point of MP3, IMO.
--
Don Melton
mailto:[EMAIL PROTECTED]
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