wte@ncrcae.Columbia.NCR.COM (Bill Eason) (05/25/88)
(Maybe rec.audio would be better for this, but I'm an engineer who has had
his fill of audio salesman talk. Read on...)
I have been shopping for a CD player at a distance until yesterday, and
the salesman I had couldn't answer my questions to my satisfaction. First,
in terms of CDs, what is x-times oversampling? My salesman explained that
the player scans the disk four times rather than just one so that it will
get "all the information on the disk. This gives you more harmonics
than you would get without oversampling." My understanding is that
the sound on CDs is already sampled at 16 bits, 44.x kHz. This should be
plenty to cover the audible range. Any harmonics over this wouldn't make
a whole lot of difference, would they? Surely the CDs aren't digitized at
88.x or 176.x kHz, are they? If not, then does oversampling mean simply
that the player scans the same bits of the 44.x kHz more times, possibly
as an error correction/detection scheme? Would a non-oversampling player
miss so many bits to make a difference? Help!
When I asked about the number of lasers tracking (something most ads hype),
the salesman told me that CD player makers "...found that the number of lasers
really didn't make any difference in how well the disc was tracked." By
the time that sentence got past my ears, it sounded more like "We don't carry
any models with that feature." What do netters think?
Finally, the player had an RCA jack marked as digital out. Anybody know about
the serial format or how to tap into this? The specific player being pushed
was a Magnavox 560, I believe, for $188. How does this sound?
"Anything you could do to help us would be . . . helpful"
- Monty Python and the Holy Grail
TIA, Bill Eason ...!ncr-sd!ncrcae!util5!wte
--
Bill Eason (803) 791-6917 ...!ucbvax!sdcsvax!ncr-sd!ncrcae!util5!wte
NCR Corporation ...!rutgers!mcnc!ece-csc!ncrcae!util5!wte
E & M Columbia 3325 Platt Springs Rd. West Columbia, SC 29169byron@pyr.gatech.EDU (Byron A Jeff) (05/26/88)
In article <3385@ncrcae.Columbia.NCR.COM< wte@ncrcae.Columbia.NCR.COM (Bill Eason) writes:
<(Maybe rec.audio would be better for this, but I'm an engineer who has had
<his fill of audio salesman talk. Read on...)
<
<I have been shopping for a CD player at a distance until yesterday, and
<the salesman I had couldn't answer my questions to my satisfaction. First,
<in terms of CDs, what is x-times oversampling? My salesman explained that
<the player scans the disk four times rather than just one so that it will
<get "all the information on the disk. This gives you more harmonics
<than you would get without oversampling." My understanding is that
<the sound on CDs is already sampled at 16 bits, 44.x kHz. This should be
<plenty to cover the audible range. Any harmonics over this wouldn't make
<a whole lot of difference, would they? Surely the CDs aren't digitized at
<88.x or 176.x kHz, are they? If not, then does oversampling mean simply
<that the player scans the same bits of the 44.x kHz more times, possibly
<as an error correction/detection scheme? Would a non-oversampling player
<miss so many bits to make a difference? Help!
<
<Bill Eason (803) 791-6917 ...!ucbvax!sdcsvax!ncr-sd!ncrcae!util5!wte
<NCR Corporation ...!rutgers!mcnc!ece-csc!ncrcae!util5!wte
<E & M Columbia 3325 Platt Springs Rd. West Columbia, SC 29169
I finally got an explanation that I understood from Hal Chamberlain's
book on Musical applications for Microprocessors.
CD players have a low pass anti-aliasing filter that attenuates
any frequencies above the nyquist frequency after converting the digital
into an analog signal. These filters must have a flat frequency response
and a very sharp cutoff. They are rather expensive to make.
What oversampling does is basically resamples the signal at 2 to 4 times
the original frequency and runs this through a digital filter that attenuates
most of the aliasing frequencies. The analog filter after the D/A can
have a much gentler cutoff because the digital filter has attenuated most
of the frequencies just above the nyquist frequency.
That's the gist of it. The CD laser mechanism runs at 44.1 kHz. The
conversion from 44.x to 88.x or 176.x is done after error correction.
BAJ
--
Byron A. Jeff
ICS Programming Lab, Georgia Tech, Atlanta GA 30332
Internet: byron@pyr.gatech.edu
uucp: ...!{decvax,hplabs,ihnp4,linus,rutgers,seismo}!gatech!pyr!byrondrg@philabs.Philips.Com (Don Gentner) (05/31/88)
In article <3385@ncrcae.Columbia.NCR.COM>, wte@ncrcae.Columbia.NCR.COM (Bill Eason) writes: > When I asked about the number of lasers tracking (something most ads hype), > the salesman told me that CD player makers "...found that the number of lasers > really didn't make any difference in how well the disc was tracked." By > the time that sentence got past my ears, it sounded more like "We don't carry > any models with that feature." What do netters think? As far as I know, all CD players have only one laser. In 3-beam players, the laser beam is split into 3 beam before reflecting off the disc. In single- beam players, the beam is split after reflecting off the disc. In either case one signal is used for data and the other two beams are used for tracking and focus correction. Both systems work, but the single beam system has the advantage of simpler design and fewer parts to get out of alignment. I don't know of any advantage of a 3-beam system, except "ad hype" -- Don Gentner Electronic mail: Philips Laboratories gentner@philabs.philips.COM Briarcliff Manor, NY 10510 {uunet,decvax,ihnp4}!philabs!gentner (914) 945-6088 philabs!gentner@uunet.UU.NET
davea@hpscdd.UUCP (Dave Angelini) (06/03/88)
I believe the three beam is faster at locating tracks or index points.
Dave strong@tc.fluke.COM (Norm Strong) (06/07/88)
In article <3608@briar.Philips.Com> drg@philabs.Philips.Com (Don Gentner) writes: }In article <3385@ncrcae.Columbia.NCR.COM>, wte@ncrcae.Columbia.NCR.COM (Bill Eason) writes: }> When I asked about the number of lasers tracking (something most ads hype), }> the salesman told me that CD player makers "...found that the number of lasers }> really didn't make any difference in how well the disc was tracked." By }> the time that sentence got past my ears, it sounded more like "We don't carry }> any models with that feature." What do netters think? } }As far as I know, all CD players have only one laser. In 3-beam players, }the laser beam is split into 3 beam before reflecting off the disc. In single- }beam players, the beam is split after reflecting off the disc. In either }case one signal is used for data and the other two beams are used for }tracking and focus correction. Both systems work, but the single beam system }has the advantage of simpler design and fewer parts to get out of alignment. }I don't know of any advantage of a 3-beam system, except "ad hype" }-- Quite right. The advantages of a 3-beam pickup are that it doesn't violate the patents owned by Philips of Netherlands. -- Norm (strong@tc.fluke.com)
severino@rb-dc1.UUCP (Cunnu the Sardinian) (06/07/88)
In article <3608@briar.Philips.Com> drg@philabs.Philips.Com (Don Gentner) writes: >As far as I know, all CD players have only one laser. In 3-beam players, >the laser beam is split into 3 beam before reflecting off the disc. In single- >beam players, the beam is split after reflecting off the disc. In either >case one signal is used for data and the other two beams are used for >tracking and focus correction. Both systems work, but the single beam system >has the advantage of simpler design and fewer parts to get out of alignment. >I don't know of any advantage of a 3-beam system, except "ad hype" >-- How do you manage to correct the tracking and focusing with 1 laser beam?? It would seem that if you split the laser AFTER it reflects off the disc you are carrying much less critical info for correcting purposes... Andrea Severino, GOULD-CSD (San Diego Division) (619)485-0910 xt. 272 ______________________________________________________________________________ UUCP : {gould|mycroft|ncr-sd|gould9}!rb-dc1!severino UUCP : {noscvax|hp-sdd|sdcsvax|ihnp4}!{gould9|ncr-sd}!rb-dc1!severino ARPA : gould9!rb-dc1!severino@nosc.ARPA BITNET: ihnp4!gould9!rb-dc1!severino@psuvax1.BITNET CSNET : hp-sdd!gould9!rb-dc1!severino@hplabs.CSNET USmail: 15378 Avenue of Science, San Diego CA 92128-3407 USA ------------------------------------------------------------------------------ "Any association with me or my company is purely coincidental"
tomh@proxftl.UUCP (Tom Holroyd) (06/20/88)
I've had two CD players stop working after a while. Two friends of mine
have had exactly the same problems with their CD players. After a while,
the players stop playing certain tracks of certain CDs, almost like the
player gets to a certain sound and can't deal with it any more. The player
just starts the piece over again, or turns off. This tends to happen more
and more frequently, and then starts happening with disks and tunes that
used to work. After a while, no CD is playable.
It isn't dirt on the disks. Maybe it's humidity (we live in Florida).
This has happened with 4 different players that I know of (a Sony D5,
a Sony Discman, and two different full size units).
Are all CD players really this bad?
Tom Holroyd
UUCP: {uunet,codas}!novavax!proxftl!tomh
The white knight is talking backwards.guhsd000@crash.cts.com (Paula Ferris) (06/21/88)
In article <352@proxftl.UUCP> tomh@proxftl.UUCP (Tom Holroyd) writes: >I've had two CD players stop working after a while. Two friends of mine >have had exactly the same problems with their CD players. After a while, >the players stop playing certain tracks of certain CDs, almost like the >player gets to a certain sound and can't deal with it any more. The player >just starts the piece over again, or turns off. This tends to happen more >and more frequently, and then starts happening with disks and tunes that >used to work. After a while, no CD is playable. > >It isn't dirt on the disks. Maybe it's humidity (we live in Florida). > >This has happened with 4 different players that I know of (a Sony D5, >a Sony Discman, and two different full size units). > >Are all CD players really this bad? > >Tom Holroyd >UUCP: {uunet,codas}!novavax!proxftl!tomh > >The white knight is talking backwards. I'm not an expert on cd's, but on mine, it has started to skip before. Seeing how it was still under warranty, I brought it back to the guy and said, "Fix it." All it was, he said, was the servo was sticking a bit. I'm not sure, but humidity could play a role in that in your area. I doubt that it would be related to the information on the disc at all. If the humidity was really bad, I suppose it could condense on some of the 'tronics and foul things up really bad. -- ====================================== End Of Message UUCP: (cbosgd, hplabs!hp-sdd, sdcsvax, nosc, inhp4)!crash!guhsd000 UUCP(pnet): (cbosgd, hplabs!hp-sdd, sdcsvax, nosc, inhp4)!crash!pnet01!guhsd000 ARPA: crash!guhsd000@nosc.mil INET: guhsd000@crash.CTS.COM CIS: 73717,226 TELEX: Temp. Disabled ...Where the streets have no name. -U2 EL CAJON, CALIFORNIA, USA (That's really close to San Diego, if you didn't know.) ======================================
langston@repoman.UUCP (06/21/88)
tomh@proxftl.Sun.COM writes: >/* ---------- "Re: CD Player Questions" ---------- */ >I've had two CD players stop working after a while. [ text deleted ] >This has happened with 4 different players that I know of (a Sony D5, >a Sony Discman, and two different full size units). > >Are all CD players really this bad? > >Tom Holroyd >UUCP: {uunet,codas}!novavax!proxftl!tomh No, Tom. All CD players are not that bad. I have a Technics SLP-8k, which I bought way back in 1984. And, knock on wood, I have not had a single problem with it. Note, this is one of the old, second-generation, CD players that has all the features of the new units, but was built in relatively small batches for an uncertain market. Yet_Another_Example_Of: "They just don't build 'em they way they used to." ============================================================================ From | Kevin Langston | the | Convex Computer Corporation | virtual | Richardson, Texas | desk of | UUCP: ihnp4!convex!langston | uses Std_Disclaimer ============================================================================