From: Mike '/m' 



Excellent commentary, thanks.

 /m

On Mon, 27 Mar 2006 11:15:48 +1200, black.hole.4.spam{at}gmail.com (Don Hills) wrote:

>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.

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