Audio DVD?

[Lennart Sorensen]

On Sat, Sep 09, 2006 at 02:17:14PM -0400, Merv Curley wrote:
> How do you keep so much information in that encyclopedia between your ears?

I don't know.  Compression maybe?

> Thanks very much,  an explanation that adds to my limited knowledge.  I 
> gathered that audio CD's were more like tape, no filesystem and just blocks 
> of data [audio]  with something called CDR in the mix. Now I have ECC 
> something or other.  I have yet to find a resource dealing with all these 
> digital audio basics.   In my ignorance I hoped a DVD was a 12" LP disk 
> compared to a 10".  Obviously the DVD electronics are quite different from 
> CD.

Well DVDs have lots of room, and they were intended for video and data.
A blip in an audio stream is hardly noticeable if a bit is wrong in one
sample, given you get 44100 samples per second.  Get a bit wrong in the
mpeg2 stream of a DVD, and you get have a nasty block mess somewhere in
your image, and due to how mpeg2 compresses, it can effect a number of
frames in a row, and you only get up to 30 frames per second, some one
bit error can screw up the image for a large fraction of a second, which
you will notice.  This means for a CD that holds 650MB of data, being
able to hold an extra 15% when just doing audio was a good tradeoff
given no one would notice, and of course they do still have some error
correction on audio CDs, just not nearly as much.  VideoCD uses the same
format as audio CD, but storing an mpeg1 stream instead of audio.  They
can occationally show artifacts of errors during playback, but they
still manage pretty impresive quality given they tend to fit about an
hour of video on a single CD.  SVCD uses mpeg2 and gets twice the
resolution of VCD in the same space since mpeg2 compresses much better.

--
Len Sorensen
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