[neil]

What allows the Panasonic portables to read through skipped CDs better than others? I'm not trying to plug Panasonic here, but what I am looking for is a technical explanation of why their's just seem to be less likely to skip on scratches..

I'm hoping that there's some notable techniclogical difference so that I can go out and find another brand that has the same capabilities (because in actuality, I'd rather not buy Panasonic, but I almost feel forced to).

 

[thomas]

The most likely reason is that the Panasonic has more agressive error correction, that does some interpolation when the data is corupted... That way, you don't hear an audiable click/skip, though what you are hearing may not be exactly what's supposed to be there...

Audiphile purists will probably prefer somthing with less agressive error correction on their reference systems, because it will always play back EXACTLY what is in the CD... But for a portable, that really isn't an issue...

 

[Mike Walker]

I would remind Thomas that "error correction" is COMPLETELY transparent. It is "error concealment" which can compromise sound quality, because enough data is missing that the unit actually "guesses" the value of the missing data. But remember, error "correction" involves COMPLETELY replacing missing data with redundant data stored elsewhere.

 

[eeyssjr]

OK. My sisters Sony mini systems plays damaged discs without a fault. You hear not a blip. But my Meridian 506.20 blips every time.

Now, obviously the Sony has better, or at least existant "error concealment" over the meridian.

What i dont understand is this. Obviously meridian thinks like you thomas - "Audiphile purists will probably prefer somthing with less agressive error correction on their reference systems"

What i dont understand is, if the data is there, the merdian plays it. If the data is missing, but error correctable, the data ends up all there again. Now wouldnt it be so much better that if the error was so large that it cannot be corrected, that an "error concealment" scheme be employed. Now although you are "filling in the blanks" its better than a blip in the music, is it not?

I mean, by error concealing, does meridian not realise that the music is NOT being degraded any further than if it was not concealed. I mean, you would hear a glitch! SO as a last resort, lie the sony, error concealment would be a wise choice.

Seems all this audiophile rubbish has gone to their head. They skimped on error concealment circuitry, and thats not what you expect for £1200.

 

[Redwoood]

I would like to add that the error-handling of a CD is based on
both error-correction and interpolation.

First it tries to recover the complete data (longer explanation of cross-interleaved Reed-Solemon codes omitted)
Only if this is not possible interpolation is used.


I think what neil wanted to know was more why panasonics play while others don't even read the disks.
I think that's more a hardware related think, maybe the optical
recognition is better and more fault-tolerant than that of other manufacturers

Bye


Redwoood

 

[eeyssjr]

Yeah Redwood. i see what your getting at. But why don't meridian see it fit to apply any interpolation, or at least an inadequate amount.

I have emailed them and never received a reply.

Its degrading to think my sisters sony player makes discs that are unplayable on the meridian for the clicks and pops at damaged sections, quite playable without ANY artifacts.

This is wrong.

As far as why diff portables wont read the disc at all, well i second ure explanation. Its the quality of the optics. A cheap laser can be too noisy etc. Seems panasoics use better quality optics. Nothing to do with the dics i would imagine.

 

[Deuce_Bigalow]

I'd have to agree with Redwood. I have a cd-r that's scratched everywhere you can see on it and its fading out, the white top of the cd is now yellow. This cd plays through in the Panasonic with some crackling noises and a few skips while my Sony will read the cd and then pretty much not play anything through the whole cd.

The Sony has enough error correction to deal with most of my cd's but I just realized that my cd collection is scratched enough I couldn't deal with a cd player that has no error correction. My Sony car cd player has almost no ability to play through scratches but I think it has a weak laser. It also failed to play one of the cd-r's I tried.

 

[Mike Walker]

To the best of my knowledge, there is no such thing as a cd player, or other digital player with "no error correction". True, error correction and concealment are far better integrated on some players than others, but I don't see how it would be possible for cd to work AT ALL without error correction. Some data is lost on even the finest discs, and particularly (dat and other digital) tapes!

I think the idea that high end cd players which cost hundreds or even thousands more necessarily retrieve more, or better sound is largely a myth. It can be clearly demonstrated that they often retrieve far less, and are quite a bit less reliable! (Of course there are notable exceptions! There is absolutely no reason that a "high end" cd player can't provide far better build and parts quality than mass market units, AND still succeed at the basic tasks of retrieving data from even damaged discs. There is no reason that a high end player can't do these things. Sadly, those which do are often the exception rather than a rule!)

In 2001 cd players represent "mature" technology. Building one correctly which sounds good, and is robust when playing good AND bad discs isn't rocket science. How sad that many are willing to pay much more money for machines which actually perform more poorly than the mass market items which "high end audiophiles" scorn! Remember...the REAL audio expert questions EVERYTHING...especially the assumption that more expensive equipment, or devices which use exotic (tubes, etc) technology for it's own sake necessarily sound better. Just as often (perhaps more often) they are audibly, AND MEASURABLY worse!

 

[Redwoood]

I don't know about the interpolation part, but the error-recovery part is absolutely necessary for a CD player to read a standard CD. It uses the same algorithms to recover valid and invalid encodings and this is all part of the CD specifications.
So every CD player must have error-correction to be able to read a CD.

 

[lini]

neil: I don't know whether this is still true (especially for portables), but at least in former times Panasonic/Technics has used a three beam optics reading the cd from different angles instead of a regular single beam solution. In my experience that actually made a difference for scratched cds.

Greetings from Munich!

Manfred / lini

 

[Redwoood]

I just wanted to add that 'audiophile purists' that don't want their equipment to interpolate anything ('to preserve the true sound, as intended by the artist/recording engineer/god') should start to clean up their system by ripping the DAC out of their CD player (unless they have seperate transport and DAC) and throw the DAC into the garbage.

At the end of the day a DAC is nothing but a device designed to convert digital input into analog output by *interpolating* a continuous signal between the discrete inputs.

And honestly, I'd rather have my system calculate 22 microseconds of music that might not sound like the original (although this is highly probable considering that musical instruments obey physical laws and therefore produce continuous and in that time frame almost linear signals themself) than reject the CD or play blips.

Though I don't really know whether you would actually hear a 22 microsecond blip, maybe subconsciously. More probable is that the transport sucks and has problems finding the right track after a read-error. Three lasers might really help in this case....

Bye

Redwoood

 

[Mike Walker]

It is myth that three beams read better than one. In a three beam system, only the center beam actually retrieves data from the disc. The other two lasers keep track of adjacent "grooves" (or pit spiral to be more accurate) and provide information to the player on exactly where to position the laser assembly at any point in time. Single beam systems use one WIDER beam which accomplishes exactly the same thing through different methodology (the beam is wide enough that it can see the adjacent "tracks" on either side, and keep the laser assembly in proper position.

Also, "three beam" systems actually optically split a single beam into three using prisms and mirrors, which can of course drift out of alignment. A more complex optical system means one more possibility of failure over time! (can you tell that I have a philosophical preference for single beam pickup? It goes way back to the early days of cd manufacture when the Philips/Magnavox based players which used a single beam could play through almost any defect, while other units with three beams were MUCH more prone to "mis-tracking").

 

[Redwoood]

Thanks for this detailed information.
I don't really know much about the mechanical magic inside cd players.

Honestly, I still think it's a miracle that something as affordable as a 50 $ CD player (with those awfully cheap plastic insides) can reliably find spmething as tiny as a CD track.


Bye

Redwoood

 

[neil]

I have a CD that has some fairly mild to significant hacks. I wish that I could send all of you the same CD and we could ALL report how that CD performed. Imagine having a sample of 100 different CD players and how they handled the skips?

I mean, shoot, just at our office alone I've tested it on a Radio Shack, two Sony's, and two Panasonics. The first three skipped, the two Pan's didn't. In fact, I was able to recreate this same outcome with a completely different CD.

I still haven't found my answer. I thought it might be in the three-beam laser theory, but that has been blown to bits by Mike Walker, Carolina Ranger. lame one, I know

So, for the sake of science, are you all willing to receive and carefully pack and send my hacked CDs from Head-Fi member to Head-Fi member? I'll mark the track # and time mark? Hehehe.. piped dream, but it sounds kinda fun.

We very well could get published in a magazine. It could be known as the Head-Fi 100 Skip Test. Step 1 - finding 99 members we can trust that will actually follow through!

 

[Odeen]

Neil, I wonder how my read-anything, copying-all-copyprotected CD's Plextor 8/20 CD-R will cope with it...

That, and www.storagereview.com has an error-correction disc that they test their optical drives with. So far, some units have perfect audio extraction with level 4 errors, but none of them can cope with a level 5 (highest)...