why do optical discs have minute limitations as well as size limitations?
 

While getting ready to burn some audio to a CD, it occurred to me to wonder why a CD is limited to 80 minutes (and DVDs to whatever their maximum time is), regardless of file size--I don't actually know. A CD also has a 700 MB limit, of course; so if you burn a set of audio files aggregating well under 700 MB, why can't they be longer than 80 minutes?

My guess is 80 minutes of audio is roughly equivalent to 700MB and both measurement limits are displayed to accommodate people using different ways of thinking. Although computer files are thought of in terms of size, CDs and DVDs were created to contain music and movies. Movies and music are measured in time, so it makes sense that time is used a measuring criterion. At least that is guess.

Audio is also recorded in "CD Quality" format on a CD, when you burn music files to an audio CD the file is converted to 2-channel signed 16-bit Linear PCM at 44,100 Hz

http://en.wikipedia.org/wiki/Compact_Disc_Digital_Audio

The different specifications are for different types of CDs you burn. When burning an Audio-CD (aka CDDA, aka Red Book) such a disc allows up to 80 minutes of audio data. When burning a data CD (aka CD-R, CD-RW, Orange Book) it allows up to 700MB of data. Keep in mind that a data CD with audio files on it (for example MP3 or OGG) is not an audio CD and the time limit does not apply.

Grab a pocket-calculator and do the math. :) Or, just look it up.

They can be longer than 80 minutes. 80 minutes is an estimate for CDDA WAV files burned raw to the disk -- an audio CD. If you burn mp3s you can fit much much more time, but at lower quality. If you burn flac then you can have the same quality but a good 20 - 30 % more time of music burned.

The only real limit is 700 MB, but even that can be stretched if need be. 700 MB is guaranteed by the factory, but you can overburn slightly if you really need to and it might just work on a number of disks.

In some cases one can overburn or oversize a disc so that it might contain more. If one does that it might not be read in all readers.

http://www.cdmediaworld.com/hardware...%20Information

That was before the time of lossy audio compression. Hence the number of samples is and therefor playing time is precisely determined. Many people on this forum might not even realize there was such a time. And 44.100 Hz was really on the edge what could be achieved in anti-aliasing filtering if 20 kHz bandwidth had to be achieved.
The reason that the time limit is what it is (and hence the capacity of of the CD) is that a design requirement at the time was that Beethoven's complete 9th symphony had to be recorded on a single disk. It is slightly over 70 minutes long.

jlinkels

The apocryphal story is: that length was chosen so that you could just fit Beethoven's Ninth Symphony on it.

CDs arent limited to 700MB, you can get 800MB and 900MB CDs. I believe that there were even some 950MB CDs produced, but they were rare even in the pre-DVDR days.

I'd guess you have CD-DA (Compact Disc Digital Audio) mixed up with a data CD with audio files on it.

That is the answer, 'Red Book'.

To follow the red book standard, a CD-DA disc must be less than 79.9minutes, 99 tracks or less, with the data 16-bit @ 44100 Hz.

It is possible to fit more onto a 700MB CD, by tricks like reducing pitch. You can also burn 90minutes to a 800MB CD, or 99minutes to a 900MB CD, but these are 'non-standard', and may not work on all CD players.

Not that you'll find many CD players that will not handle the non 'red book' formats these days.......