Yep, there would be a difference but the higher the ABR then the smaller the
difference between the resulting file and that encoded using high quality
VBR. For example, if you set your ABR to 300kbps then ABR would steal a
little from less complex parts of the music and use those to supplement
parts of the music that are more complex and need more than 300kbps. The
result is that ABR will try to maintain a jagged line around the 300kbps
mark so imagine it just dropping slightly above and below the line through
the music track. With VBR with a maximum of 320kbps then you are guaranteed
that if a long part of the track needs 320kbps then it will get that. You
don't have that guarantee with ABR because it may not have enough bits in
hand from the less complex parts of the track to maintain 320kbps for the
same amount of time and may instead cap it at 310kbps.
ABR is a poor man's VBR where it is important that you can predict the file
size. Much better than constant bit rates of less than 320kbps though. For
example, a file at ABR of 256kbps will sound better than a file encoded with
a constant bit rate of 256kbps. The reason being that the ABR file will be
fluctuating just above and below the 256kbps mark as required whereas the
constant bit rate will have been crudely chopped as soon as it needed to go
above 256kbps.
Regards.
Kevin
E-mail: kevin.llo...@sky.com
----- Original Message -----
From: "Amie Slavin" <amie.sla...@ntlworld.com>
To: "'PC Audio Discussion List'" <pc-audio@pc-audio.org>
Sent: Wednesday, December 30, 2009 12:28 PM
Subject: RE: Pros and cons of varible bit rate
So is there any difference between ABR set to a higher bit rate and VBR
with
the quality set to the highest?
Amie
-----Original Message-----
From: pc-audio-boun...@pc-audio.org [mailto:pc-audio-boun...@pc-audio.org]
On Behalf Of Kevin Lloyd
Sent: 27 December 2009 14:00
To: Kevin Lloyd; PC Audio Discussion List
Subject: Re: Pros and cons of varible bit rate
and here's a reference to the choices around minimum bit rates when using
VBR:
CDex Manual
File Edit Bookmark Options Help
Contents Index Back Print Up << >>
Bitrate Options:
There are three types of bitrate options that you can specify for each the
encoder (although some encoders may not allow any options).
1) Constant Bitrate (CBR)
This is the default encoding mode, and also the most basic. In this mode,
the bitrate will be the same throughout the whole file. So, a second of
audio
from one
part of the file takes just as much disk space as a second from any other
part of that file -- regardless of whether either part is silence,
acoustically
simple, or
quite complex. This means that you are likely to hear distortion more in
the complex parts than in the simple parts. The advantage of CBR formats
is
that
even
older players understand them, and that you can reliably predict the file
size from the duration of the sound (or vice versa).
2) Average Bitrate (ABR)
In this mode, you tell the encoder to aim for an average bitrate that you
specify, skimping on the simpler parts of the music, and using higher
bitrates
for the parts
of your music that are more complex. The result will be of higher quality
than you'd get in a CBR encoded file of the same size. This mode is highly
recommended
over CBR. This encoding mode is similar to VBR.
3) Variable bitrate (VBR)
In this mode, you say what level of quality you want in the output file,
and
the encoder compresses each second as best it can to get just that level
of
quality --
using less information to represent simpler parts of the song, and more
information to represent the more complex parts. However, this mode relies
heavily
on the
encoder's model of how you perceive quality, and could lead to a few "bad
choices" in the encoding process. If possible, you may want to specify a
minimum
bitrate (e.g., 64 Kbps) to avoid those potential errors.
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