This is an explanation, brief though it may be, of CD-ROM drives and
computers, relating mostly to audio CDs.
The cdrom drive has existed in its current format for some years now,
and as such has become standard. There are several connections. Usually,
from right to left, they are power, IDE/SCSI connector, jumpers for
master/slave or SCSI ID, digital audio, and analog audio. I have never
come across the digital audio connector in use but that doesn't mean it
isn't done, just that I'm not all that familiar with it. Simply, when
your cdrom drive plays an audio cd, either by pressing the play button
on the front panel, using gnome's cd player, or winblows' old cd player
program, a command was sent via the the IDE bus to the cdrom drive
(unless it was the button on the front in which case it's already there)
that tells the drive firmware to play an audio cd. All the cd audio
"decoding" is done in the drive itself and the resulting audio is output
through the headphones connector on the front (if there is one), the
analog audio out connector on the back, and the digital audio out
connector on the back (that's digital like your modern stereo has a
digital coaxial connection, though it's actually an RCA connector. Don't
get confused with the coaxial that is used for most TV signals still.
"Coax" in concept but it's not a noun.) Audio cds can, and often now
are, played "digitally". This is where the software on the computer
reads the cd just like a data cd, sector by sector, and reads the audio
in a data format off the cd, decodes that in to a format appropriate for
your sound card, and outputs it to the soundcard. When you rip a cd
nowadays, it's probably using this same method because you can read the
data (audio) at the highest speed the drive supports, i.e. 56x, and
proceed to encode to your favourite format (OGG, for example), as
opposed to playing every song analogly at the speed it was intended to
be listened to which would result in it taking up to 80 minutes to rip
the cd.
In order to cut costs on computers, manufacturers have cut back where
they can. Winmodems being a biggie, but also no longer including the
audio cable that connects the cdrom's analog audio out directly to the
soundcard. This has several benefits for both system manufacturer and
end user. One, without an audio cable and by using the data directly,
you can get clearer sound because there will be no interference. This is
the very same reason why the FCC is mandating DTV, the digital signal
will weaken with distance but it will not degrade; a one is still a one
and a zero is still a zero no matter how faint. Two, a couple cents here
and there does mean a lower cost of manufacture which means they don't
have to charge as much to make the same profit; lower prices are
obviously, more desirable for both parties in the transaction.=20
The reason winblows works is because quite frankly, they have to. They
need (in their opinion only, not mine) to keep up with what the system
manufacturers are doing and so by default, their cd player software will
play via CDDA (compact disc digital audio) and no one will notice the
difference. F/OSS tends to be a bit more legacy compatible and default
and so, for example, gnome cd player still plays the "legacy" way which
is the command sent to the cdrom drive which then plays the cd and
outputs the resulting sounds to the soundcard. Other software, such as
XMMS, can play cds digitally with a plugin, often included with the
distro.
Just a note, you can tell whether your CD is being played digitally in
most media players by whether or not a visualisation is available. If
you're playing the disc analogly, the computer/software doesn't process
the audio in any way and therefore, can not show any pretty pictures in
beat to the music or whatnot.
I hope this clears things up a bit for everyone.
Bryce
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