From: black.hole.4.spam{at}gmail.com (Don Hills)

In article , "Rich Gauszka"
 wrote:
>This may be a dumb question but I've seen some quotes like those at the link
>below that give priority to VBR. Is this a bit of misinformation?
>
>http://www.mp3machine.com/news/842/

Nope. It's good info, as far as it goes. The bitrate for MP3 can be set
anywhere between 32Kbps and 320Kbps. 256Kbps or 320Kbps usually sound
pretty close to the original CD sound, and it takes a high quality CD and
playback system (and some training) to be able to tell a difference. As the
bitrate drops, you will notice more and more effects - a dulling of
percussive sounds, continuous notes (flute etc) cutting in and out, and odd
warbling, whistling and chattering sounds.

One demo I've done for various people is to take a music track and mix it
with a steady tone from a signal generator, with the tone at a level that
is lower than that of the music but still clearly audible if you listen for
it. I then encode it at various bitrates. At lower bitrates, the tone
starts to disappear in places where the decoder judges the tone well enough
masked by the music. The lower the bitrate, the more ruthless the encoder
has to be about throwing away information.

Music varies in complexity throughout the track. A CBR encoder always has
to trim the music down to fit the bitrate, rewgardless of its complexity. A
VBR encoder can adjust the bitrate as required in order to accomodate the
varying complexity of the music. 128Kbps CBR was originally chosen as an
acceptable compromise between quality and file size for non-critical
listening, especially in environments where there was significant
additional masking noise such as in-car, on public transport and in public
places. I'm sure you've noticed that "road rumble" in your car
effectively masks the bass notes, for example. Although the MP3 encoding
spec allows for a variable bitrate, most of the original decoders and
portable players didn't have the smarts or processing power to handle VBR.
Many portable devices originally only handled a couple of CBR values such
as 64 or 128Kbps.

Glenn uses 320Kbps CBR for radio work. File size is obviously less of a
problem to his customers than maximum compatibility with older equipment -
broadcast stations don't replace their players every year or two. For
private use, it depends on your requirements. If sound quality is important
to you, *and* a significant part of your listening time will be in a quiet
environment using good equipment, then go for either 256Kbps or 320Kbps
CBR, or high quality setting VBR if your decoding equipment handles VBR. I
ripped a lot of my CDs to MP3 back when I was working in an office, in a
fairly noisy environment. Even with the noise, I found that I could still
hear coding artifacts at 128Kbps CBR (the de facto standard then). I didn't
have the disk space for a higher CBR, so I experimented with VBR and found
a quality setting that sounded acceptable and still only increased the file
size by about 10 to 15% over a 128Kbps file.

--
Don Hills    (dmhills at attglobaldotnet)     Wellington, New Zealand
"New interface closely resembles Presentation Manager,
 preparing you for the wonders of OS/2!"
    -- Advertisement on the box for Microsoft Windows 2.11 for 286

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