[LMB] MP3 advice

[Mark Allums]

Meg Justus wrote:
> Um, is there any way people can discuss all this in terms of audiobooks 
> rather than music in so far as capacity stuff is concerned?  Pretty please?
> 
> Mark:
> An MP3 CD is already compressed, so there is no savings when you move it
> to the hard disk.  If an audio book MP3 CD uses 2/3 of a standard CD, it
> will take about 400-450M.  If it used the whole CD, it would take the
> whole 650M.
> 
> How can I tell how much space an MP3 CD audiobook will take on the hard 
> drive/MP3 player before I upload it on my computer?  I'm not seeing anything 
> on the packaging...

Put the disk in a PC drive and use the power of Windows to find out.  On 
data discs (which is what an MP3 CD is) go to My Computer, right click 
on the icon of the drive containing the disc, and choose Properties. 
The information is right there in the box that pops up.

This won't work for audio discs.  With audio discs, it requires you to 
be clever.  I use an old third party ripper program called Audiograbber. 
  When you start it, it brings up the tracks on the disc and 
automatically displays their length in MB.  To get the total, I have to 
add up the individual tracks, but other software can give you the same 
information.    However, this is of less concern, because for audio, you 
will be compressing the audio, and the figure of merit will be the size 
of the compressed track.


> So far there've been three general answers about size, all three of them 
> wildly varying.  I'm trying really hard not to feel stupid about this, but 
> the two that seem to matter are:  regular CD audiobook:  500-700 meg, MP3 
> audiobook of the same book length: 100 meg.  Is that right?  So 10 books per 
> gig?  Roughly?

Sort of, yes.  Any CD holds 650 MB of data, whether it is a data CD or 
an audio CD.  An audio book that is a regular CD that will play in any 
CD player will use an amount proportional to the length of the audio 
track.  If the CD is 74 minutes long, it will fill the CD completely and 
use all 650 MB.  However, if you like, you can rip that CD to MP3, and 
the same 74 minutes will use a much smaller file.  For voice recording 
(not music) you can use a fairly low bit-rate, about 64 kb/s.  This will 
allow you to fit that 74 minutes into a file about 1/10 the size of the 
original, or about 65 MB.

An MP3 audio book that is the same time length as the above will use 
less storage space on the CD, about 1/10 as much.  Most MP3 CDs take 
advantage of this to fit more audio on the disk.  So, a book that takes 
ten hours to read can be fit onto one CD.  The amount of space it takes 
of course depends on the length of the audio.  But if it takes a whole 
CD, it will need all 650 MB.

The 1/10 figure I quote is an estimate based on a very low bit-rate.  A 
higher sound quality with a higher bit-rate will lower the amount that 
will fit.

So yes, you have got the gist of it.  The confusion stems from mixing 
audio CDs with MP3 CDs.  Audio from audio CDs can be compressed.  Audio 
from MP3 CDs is already compressed and can't be compressed further.

1G can hold up to 24 hours of audio if highly compressed.  Your mileage 
may vary.

Hope this helps.  :)

--Mark A.