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RE: Cd reading errors correction systems impact on sound.

Posted by Thorsten (M) on June 16, 2015 at 05:59:47

In Reply to: Cd reading errors correction systems impact on sound. posted by beppe61 on June 14, 2015 at 07:46:18:

Hi,

First, error-correction is exactly that, errors are corrected. Extra information is carried together with the "payload" data and any error that is correctable will be corrected. After this there is no error. Thus error correction in itself cannot cause audible differences.

Second, if an error cannot be corrected the CD-Player will attempt a number of approaches to "conceal" the error, like repeating the previous sample, interpolating between adjacent samples etc., eventually corrupt samples may be muted. This process of error concealment will cause audible artifacts all the way to the sound cutting out.

It should be noted that on a CD in good condition uncorrectable errors are incredibly rare. And one sample worth of error concealment is likely to remain inaudible in practice.

Knowing all of this leaves an interesting question. How do "CD Tweaks" (be it special cleaning, green painted edges, the l'CDFlop mat and so on) possibly make any difference? After all, the data is there 100% complete.

The answer is as so often jitter and crosstalk from circuitry that should be isolated from each other.

If you look at the motors and Focusing electromagnets in a CD Player and at the driver circuitry, you realise you are dealing with a kind of Audio Band amplifier here, which has greatly varying current if for example the CD is not completely flat.

If you look at common commercial CD-Drives, you will see that very rarely is there any serious isolation between the clock ground/supply and the servo drivers. In fact, most of the common PCB's almost everyone uses (no matter if it is a Philips CD-Pro, a Neo something mech etc.) are appallingly bad in this respect.

You can literally correlate clock jitter and servo current (using suitable test gear. And sure, you apply tweaks to the CD and see the impact on servo current and jitter. And unsurprisingly, if you play the CD in the same room where the speakers create vibration, you can see the impact of that vibration in the servo current and so on and if you modify vibrations using (say) damping or different feet - well you can see that too using suitable instrumentation...

The solution? Make sure the clock has an independent supply and and a ground layout that avoids contamination from the servo circuitry. Give the Servo the biggest value local electrolytic bypass cap's you can find and fit and ideally make a separate supply only for the servo Power Stage.

If you then can re-clock the data leaving the transport (be it I2S or SPDIF) against your squeaky clean clock before sending it on, and you will find the resulting transport most resistant to tweaks...

Of course, that usually means you need to either dramatically modify the PCB that comes included with your drive solution one at a time or you design your own, including software and everything.Few HiFi makers actually do that.

Thor

At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to intolerable pain. Really, what more could we need?

Edits: 06/16/15

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