Why CD players will never be dead

Mr. Tennnis - I will put my product where my mouth is. You put the money down. A bet requires both of us to have skin in the game.

BTW, did you read the Dec. Stereophile?

Steve N.
Empirical Audio

11-27-11: Ghosthouse
How is it possible for a copy of a CD played from a computer hard drive to sound better than the original CD?

Some good responses have been provided above. The following excerpts from this thread provide further elaboration on some of the things that have been touched upon:

07-19-11: Shadorne
If a disc wobbles while it spins then this may cause cyclical adjustments to the pick up laser servo and these repetitive draws on power may induce variations in the clock through the power supply.

07-20-11: Kirkus
CD players, transports, and DACs are a menagerie of true mixed-signal design problems, and there are a lot of different noises sources living in close proximity with suceptible circuit nodes. One oft-overlooked source is crosstalk from the disc servomechanism into other parts of the machine . . . analog circuitry, S/PDIF transmitters, PLL clock, etc., which can be dependent on the condition of the disc.... One would be suprised at some of the nasty things that sometimes come up out of the noise floor when the focus and tracking servos suddenly have to work really hard to read the disc.

The following excerpt from this paper by Steve reinforces the point about jitter that he stated above:

3. Jitter from the pits on a CD:
These are the pits in the CD media that represent the recorded data. Variation in the spacing of these pits result in jitter when reading the data. Commercially CD's created from a glass-master generally have more variation in the locations of the pits than a CD-R written at 1X speed on a good CD-R writer. Even though most modern CD players have buffering of the data to create some tolerance to this jitter, there is usually a PLL (Phase-locked-loop) involved, which is still somewhat susceptible to jitter. To determine if your player is susceptible, it is a simple experiment to re-write or "clone" a CD and then listen for playback differences from the commercial version. For newer players that completely buffer the data at high-speed from a CDROM reader to a memory buffer, this jitter is not an issue.

Of course, having the digital source and the dac in separate components creates other ways in which jitter can be introduced, especially if synchronous interfaces such as S/PDIF, AES/EBU, or adaptive USB (as opposed to asynchronous USB) are used. And as usual the quality of a given implementation, or lack thereof, can be a more significant factor than the approach that is chosen.

BTW, not to belabor an issue of semantics, but what is being referred to as "error correction" is more properly called "error interpolation" or "error concealment." "Error correction," which as I understand it occurs many times during the reading of a typical cd, is by definition bit perfect, i.e., the error is corrected! See this Wikipedia writeup, and this one.

Regards,
-- Al

hi steve;

the bet would be your transport + a dac of your choosing vs my cd palyer.

taking note of your statement regarding comparing transports, assuming your transport is superior to the laser mechanism in my cd player, the dac section and any mods to my player, i conjecture would be preferable to your (supposedly better ) transport and dac.

thus i have no interest in comparing transports. rather i am interested in one digital source vs another.

if you recall my visits to your rooms at the st tropez, you may recall that our tastes in sound diverge.

so i will spare you a bet that you cannot win.

the whole purpose of my statements is to indicate that our hobby is subjective.

i have only found one digital front end that i prefer to my cd player, namely the original zanden and its companion transport.

i will assume that you fabricate a fine product but i doubt it sounds like the original zanden or the original lector.

" "Error correction," which as I understand it occurs many times during the reading of a typical cd, is by definition bit perfect, i.e., the error is corrected!”

Hi Al, please take this as a question and not an argument: If information (bits) is missing from a read, how does a CDP know what that information is. It was my understanding that error correction/interpolation/concealment is a process where the CDP makes a sort of guess based on the before and after the error bits. Okay Steve, blast away :-)

11-28-11: Phaelon
If information (bits) is missing from a read, how does a CDP know what that information is. It was my understanding that error correction/interpolation/concealment is a process where the CDP makes a sort of guess based on the before and after the error bits.

Hi Tom,

Good question. The answer is that what are called "error correcting code" bits are encoded onto the CD, in addition to the audio data (and other) bits. As explained in the first Wikipedia writeup I linked to, those bits implement mathematical algorithms which allow errors in the associated data bits to be detected, and if the errors are not extremely severe (as may result, for instance, from a particularly severe scratch on the CD), also allow the exact original data to be determined.

That process is performed by the transport mechanism's electronics.

In the far more rare event that the errors are too severe to be precisely corrected, then interpolation (aka concealment) is performed, which as you realize amounts to an estimate or guess as to what the data should be. Or in extreme cases the CDP may mute, or if a non-realtime read mechanism such as a computer or the Perfect Wave transport is being used, multiple attempts may be made to read the incorrect data.

Note this sentence in the Wikipedia writeup:

The result is a CIRC [Cross-Interleaved Reed-Solomon Code] that can completely correct error bursts up to 4000 bits, or about 2.5 mm on the disc surface. This code is so strong that most CD playback errors are almost certainly caused by tracking errors that cause the laser to jump track, not by uncorrectable error bursts.

Best regards,
-- Al