| Title: | Welcome to the CD Notes Conference |
| Notice: | Welcome to COOKIE |
| Moderator: | COOKIE::ROLLOW |
| Created: | Mon Feb 17 1986 |
| Last Modified: | Fri Mar 03 1989 |
| Last Successful Update: | Fri Jun 06 1997 |
| Number of topics: | 1517 |
| Total number of notes: | 13349 |
Eight-to-fourteen modulation. EFM.
What exactly is it?
What is the purpose of it?
-mike z
| T.R | Title | User | Personal Name | Date | Lines |
|---|---|---|---|---|---|
| 1285.1 | General Idea.. | MQFSV2::LEDOUX | Reserved for Future Use | Mon Aug 01 1988 12:46 | 26 |
The following is from memory, I read that, I forgot where..
Very *Basically*, EFM is:
Based on the fact that we have to keep "in sync" there cannot be
more than 2(or is it 3?) zero's contiguous, otherwise the sync
can be lost. If you have a very low signal (say, 2 seconds of silence)
can give a signal of binary 00000000 00000000. Since *only transitions*
are written you would get frames with no sync at all for 96 bits time.
First, the most significants 8 bits are taken (00000000) and are
modified by a computer to something like this: 00100100100100.
(0924 hex). When read the computer knows that 0924 = 00 hex in reality.
And feed the Digital to analog accordingly.
The same for the lower 8 bits.
Note that the above example is totaly fiction, I have no idea
if 00 hex = 0924 hex on the disk.
Writing that way actually save space for close to 25%.
Unless someone has seen otherwise...
Vince.
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| 1285.2 | another soul wandering around in the dark | CTHULU::YERAZUNIS | A little boy shows you his butterfly collection... | Mon Aug 01 1988 17:47 | 8 |
I thought EFM just mapped each eight bit signal into 14 bits, with
some bits replicated and then negated, to gaurantee that no excessively
long string of either 1's or 0's got through...
(Where does your analysis put the Fire ECC?)
-Bill
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| 1285.3 | while I'm on the subject ... | ANT::ZARLENGA | Righetti's got the juice back!! | Mon Aug 01 1988 19:49 | 5 |
Is there a book/manual/etc that explains all the technical
workings of today's CD players?
-mike z
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| 1285.4 | nothing? | ANT::ZARLENGA | Jeff, wake up! Don't fall asleep! | Sun Aug 14 1988 00:08 | 0 |