[78-L] Record playing speed ^

[Mike Richter]

P G C wrote:
> Ok there were 80, 78, 33 1/3 then 45 and even 16 rpm (my aunt had one of these).
> 
> But, is there a standard spining speed on a CD? (what does it mean 1X, 2X, 16X, etc. in the CD-ROMS?)

A CD-DA (Compact Disc - Digital Audio) plays at 44.1 ksps - 44,100 
samples of four bytes each per second. As others have written, that 
means constant linear velocity on each disc - but the rotation speed 
varies depending on radial position on the disc.

44.1 ksps is "1x" for reading and writing. The rated speed on the 
package is that which may be achieved under ideal circumstances for some 
instant in the read or write process. It is essentially a publicity 
number of little practical value. There is an optimum write speed for 
any combination of writer and medium (with a slight influence from the 
type of write involved); that is a more significant but unpublished 
attribute.

Note that many playback devices - CD-ROM drives, portable CD players, 
etc. - will read CD-DA at higher speed than 1x, then stop reading and 
even begin spinning down the disc while the read buffer empties. Such 
operation is essential to suppress skips, but makes the 1x speed of 
conventional playback an average value, not an instantaneous one.

There's more on this in the primer on the CD recording side of my WWW site.

Mike
-- 
mrichter at cpl.net
http://www.mrichter.com/