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CD Player VS. Computer-DAC-Amp  

2010-11-13 13:49:02|  分类: 默认分类 |  标签: |举报 |字号 订阅

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Let me explain (in my limited understanding). A cd is digital. If there are no scratches on the disc, it will be read identically each time it's played. If my system has a good DAC component, why would i need a good cd player? As long as there's a digital output, would each and every cd player read the same data off the same disc? The DAC would do all the sound work, right?
Thanks.

There are 3 blocks actually: 1) the mechanical part (reading of data) 2) the digital to analog circuit itself and 3) an analog stage that amplifies the signal so as to meet standard line levels of amplitude and impedance. A crucial piece connecting blocks 1 and 2 is the clock, that serves as the absolute reference of timing and frequency to undo the process of codification of the data in digital form done by the recording company. Lots of issues can then arise: some mechanical, some electronic. A standard DAC unit actually corresponds to blocks 2 and 3. The units referred to as "transports" correspond to block 1 (spliting a CDP intro transport and DAC makes the clock task more difficult and this may cause some degradation of the sound). One of the main issues of block 1 is jitter (an audible effect due to, among other things, the necessity of rereading several times the same data and applying to this temporal sequence correction software so as to make sure that the errors in the data reading are minimal). Another mechanical issue is the effect of mechanical vibrations on the digital signal produced, The performance of the DAC itself depends on the quality of the chipsets and the clock used, and on the design used to accomplish this (there are several possibilities, with very different strategies that end up in different types of sound). Finally, the quality of the output analog amplification stage is very important: one thing is to have vacuum tubes there, another to have discrete selected transistors and yet another to have an integrated circuit that does it all. This is a sort of overlooked area in which the high end CDPs show lots of differences with respect to middle-of-the-read CDPs.
Some high end brands, like Naim or Bryston insist on the idea of having a CDP and not having a transport+external DAC approach (quote from http://bryston.com/bcd1_m.html : The advantage of an all in one box solution for a CD Player (as opposed to a separate outboard DAC and Drive) is the elimination of jitter. For optimum performance the Drive and DAC must use the same MASTER CLOCK. If the clock signal of the drive is not synchronized with the clock signal from the DAC then jitter develops. In external DACs the digital input must be re-clocked in order to reduce the jitter. Jitter is defined as mistiming of the digital signal. The timing of all those ones and zeros is of extreme importance. It isn’t enough to get the bits right; those bits have to be converted back into music with the same timing reference as when the music was first digitized. These timing errors (jitter) are the bane of quality audio. With the Bryston CD player the master clock and the drive are synchronized perfectly to eliminate any possibility of jitter affecting the sound quality of the player.)
As people have said, all of this yields audible differences. If I had the money to spend on a premium CDP (say, a Naim or Electrocompaniet unit costing 3000+) I would gladly do so.
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