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mikewu99 16th January 2003 09:33 PM

Newbie CD transport question
What makes high-end CD transports expensive? From what I have been able to pick up, enormous effort is made in reducing jitter at the output of the transport (S/PDIF data stream). The DAC then expends considerable effort recovering the clock from the S/PDIF with low jitter.

Why not put an ultra-low jitter clock on the DAC, put a FIFO before the DAC, and use a simple servo loop to slave the transport clock to the DAC clock? The servo would just have to be good enough to avoid data over or underruns in the FIFO.

What other functions are typically done by the transport? Error/skip correction? Am I missing something fundamental here? :confused:

I apologize if this issue has been discussed before, I'm a newbie and didn't find much while searching the forum.

Elkaid 16th January 2003 09:42 PM

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Several manufacturer put a lot of effort in vibration damping mecanism.

TEAC (and probably many others) has a system called VRDS which is pictured below.

I suppose that's it's a way to justify a part of high price CD transport.

till 16th January 2003 09:54 PM

this suspension and anti vibration stuff is what a manufacturer is easyily able to do, not too expensive, consumer belive it improves something, and its usefull for the marketing guys... ok, maybe it helps - but does a well designed transport needs this addidtional stuff?

take a look at different transports.

Mr. Thevissen from daisy laser explayned me, if i understood him right, there are two kind of transport. Those that sell for about 6 USD each if you buy >1000, and those that are >200USD each. One difference is software, another how stiff is the construction (have a look at CD PRO 2)
- and main difference if there is electronics behind the laser on the moving head (good, expensive, less errors) or is there only the laser diode on the moving head and a "long" (few inch?) cable to the electronics (cheap, head has less weight, weak actuators possible... and more errors because signal from diode comes with lot of noise or so)

mikewu99 17th January 2003 12:10 AM

I guess my question is why the vibrations need to be damped to such an extreme. Is the bit error rate (BER) actually significant in a poorly damped transport? If the data can be synchronized with the DAC clock, then it seems to me that the only thing that matters is an acceptably low BER.

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