Bit-perfect: Error correction, interpolation, and a "dirty" laser lens?

[Beauregard]

If I remember my intro to CD course correctly, the error correction capabilities of a CD transport result in bit-perfect data transmission while interpolation doesn't. However, interpolation is rarely required so doesn't usually have an effect on the data stream.

I just added the DAC1 to my system and am wondering if I should clean the lens of my 10-year-old CDP. It was used in a heavy-smoke environment for the first five years of its life and cleaned periodically with a commercial cleaning disk. (No, I didn't quit... just can't smoke in the house any longer.)

I'm having absolutely no probs with the player and I tend to be a don't fix it if it ain't broke kinda person. But I also have a compulsive streak and am sorely tempted to take the player apart and clean the lens with a microfiber cloth to make sure I'm getting bit-perfect data to the DAC.

Does anyone have any idea if a moderately dirty lens would increase the frequency with which the circuitry needs to invoke interpolation with its attendant degradation of audio quality? Or is it likely that the error correction is accommodating any problems resulting from a less-than-crystal lens?

Yeah... an odd question... Then again, this is a pretty odd place!

Thanks much,
Beau

 

[jefemeister]

A dirty lens can definitely lead to trouble. be VERY careful when cleaning it though as a scratch is even worse. Use all the same material/techniques you use when cleaning a nice camera lens. Also, get rid of your lens cleaning CD. I assume you're talking about one of those CDs with a little brush attacted to the surface. Using them is just about the worst thing you can do to your CD player apart from dropping it.

 

[Sovkiller]

Quote:

Originally Posted by jefemeister Also, get rid of your lens cleaning CD. I assume you're talking about one of those CDs with a little brush attacted to the surface. Using them is just about the worst thing you can do to your CD player apart from dropping it.

Really? Why they recomend the use of them then, could you be more specific on why we should avoid the use of them. I mean I was using them for years with no problems, I use one made by Allsop, Carbonedge or so, anything wrong with that??? Which is the best way tehn ot clean the lens, and how often do we need ot do that...

 

[gerG]

A couple of comments based on a lot of experience with laser optics, mostly the kind that will vaporize themselves if a friggin spec of dust gets on a mirror or lens:

Jeff is correct, a scratch or strong singularity will play hell with laser source optics. Extreme care is advised.

CD transport lenses act as both transmitter and receiving optics. To follow the disc surface they are built into a servo actuator that moves them quickly along the axis perpendicular to the surface of the disc. The lens is basically mounted in a voice coil and suspension that moves it rapidly toward and away from the disc. The mechanism is extremely delicate, and can be broken by too much pressure to the lens.

I can't imagine how any disc mounted apparatus could possibly get the lens clean, but I could be missing a trick. I usually dismiss those cleaning discs as a gimmic/placebo.

I clean my lenses with a clean nylon glasses cloth. I have used all sorts of solvents and fabrics, but I have found nothing that cleans better than condensed water (breathe on the lens) and a glasses cloth or microfiber cloth. This should tackle anything present on a CD transport lens.

Before cleaning, inspect. Get a decent white LED flashlight. I have found nothing better for lighting up crud on a coated optic. If it is not dirty, don't mess with it!

My technique for CD and DVD lenses is to onplug the player, open it up, and gain access to the lens. Inspect with the LED light first. If it is not hazed or cruddy, re-assemble and leave it alone. If something is there that should not be, try to blow it off (gently) with either dust off or a lens bulb (squeeze blower available at camera shops). If that does not work, wash hands, fold up a clean lens tissue or nylon lens cloth without touching the part that will be used, breathe on the lens to fog, and gently clean with the corner of the folded cloth. One pass usually does it. Re-inspect, and repeat once if necessary. If crud is still present, there is something more tenacious on there, or it is on the other surface (which you cannot get to). Professional help is advised at this point.

My experience only, and I am certainly not a CD player technician.


gerG

 

[Beauregard]

Thanks for the replies!

Special thanks to gerG for taking the time to provide so much info and instruction. I'll definitely take your advice.

One question about which I feel a little embarrassed... Just what is a white LED flashlight and where do I find such a thing?

Appreciatively,
Beau

 

[Nak Man]

Great info ! I also wonder about that brushmounted CD, as it practically accomplish what manual cleaning try to do - in a more controlled way ? After the trauma of trashing my very first CDP using cotton buds within a week of using them back in 85

I've been extremely careful with the lens assembly. I use cdp cleaner / tiny brush on a disc whenever possible before resorting to manual approach. I agree that we need to inspect the condition first as I feel too much physical contact there is not good for lens' health. But once the case is opened, I'm tempted to clean them manually instead of doing it at 300 rpm. =)

Quote:

Originally Posted by gerG breathe on the lens to fog, and gently clean with the corner of the folded cloth.

I dip the triangular shape of cloth edge in glass windows cleaner (windex ?) solution / foam and *gently* brush the lens. Quickly blow with squezze lens blower instead of letting it dry by itself or blowing by mouth.

 

[gerG]

Hi Beau. LED flashlights are available all over the place these days. They are an application of the new generation of high output LEDs (up 5 watts!). I highly recommend the Inova X5 for general use. Also the UK is about the best bang for the buck (it uses a 1 watt luxeon star, takes AA batteries, and is rugged as a rock). These are general use lights that will have you throwing away the old maglights. For occasional lens inspection there are cheap single low watt LED lights that will work fine. Hunt around on that website. Also candlepowerforums.com is the equivalent of head-fi for the illumination obsessed. Make sure that you get a white one. Blue, red, and orange LEDs are cheaper, and some manufacturers would prefer to sell you those for the same price as the white ones.

Nak, good work in improving your technique! Repair shops make a lot of money replacing transports for people who tried to clean their lens and did not realize how delicately suspended it is. I would personally avoid commercial glass cleaner, since it will typically leave deposits on coated optics. The nylon lens cloth removes oil (which coatings just loooove) without solvents. A tiny bit of de-ionized water is all that is needed, which is what breathing on the lens does. Those little cloths are available at camera shops, and are a miracle for care of optics.

gerG

 

[Beauregard]

gerG,

Once again, thank ye!

The folks who populate this place are great...

 

[djbnh]

GerG, nice links for the flashlights. Here in rural NH, with the winter storms and Nor'easters, it's a help to have something reliable other than candles and lanterns when the power goes out.

 

[bLue_oNioN]

The Inova X5 is definitely a very solid flashlight, I've got an Inova X5T myself.

 

[Beauregard]

Aaargghh... seems fitting to give a public announcement of the passing of my Marantz CD63-SE which has provided so much pleasure for so many years. And was the object of this thread.

She spit, farted, and died this afternoon at 14:35 GMT - 5 while in the process of delivering a smooth (though tobacco-tainted) stream of bits and bytes that the DAC1 turned into Schubert lieder.

RIP, dear lady.

And forgive me for rushing into the arms of a Cambridge Audio 340C Azur. She'll be youthful, unstained, and (hopefully) bit-perfect... but she'll never match your charms.

Sadly,
Beau

P.S. I never got to clean the lens but at least I have one very nifty flashlight arriving this week!

 

[zaguar]

Can any random $50 cd player with optical out and a DAC1 compete with a $3000 cd player, again using the dac1 though dac1.

BTW, is SPDIF the same as optical out?

 

[lini]

Quote:

Originally Posted by zaguar BTW, is SPDIF the same as optical out?

No, not neccessarily. Actually, S/P-DIF (Sony/Philips Digital Interchange Format) comes in two basic flavours, which are either optical (with Toslink or optical 1/8" connectors) or electrical, the latter often also being called coaxial because of the connectors (usually RCA, sometimes BNC) and cables being used for that purpose. In addition, there are the professional differential electrical S/P-DIF variant AES/EBU as well as the electrical S/P-DIF variant with TTL signal level found on computer optical drives and internal soundcard connectors (CD Digital In).

Greetings from Hannover!

Manfred / lini

 

[yage]

In the compact disc digital audio (Redbook) standard, error correction for reading the data off the disc is built in.

Look here:

http://hyperphysics.phy-astr.gsu.edu...o/cdplay4.html

And here:

http://www.everything2.org/index.pl?node_id=482691

Even mark levinson acknowledges that errors from laser reads are a minor problem (from http://www.marklevinson.com/products...t=cd&prod=no37):


Quote:

Recovering the correct data, by itself, is not difficult. The error detection and error correction schemes used by all modern CD players are quite powerful. Since the technology used for compact discs borrows heavily from computer technology (where even a single error can cause a system "crash"), you might imagine that uncorrectable errors would be quite rare. If so, you would be right. Even badly scratched discs can often be played without difficulty.

So if the player is working fine (i.e. playback doesn't stutter or skip around frequently) then the laser pickup is functioning normally. Hope this brings you some peace of mind...

 

[zaguar]

Guten Tag! Was sprechen sie? Anglais, deutsch, und....?