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CDP As Transport - Information?

post #1 of 3
9/8/08 at 6:26pm
Thread Starter 
I've been doing a fair bit of reading on the subject, but I'm still a little ambiguous on just what it means to use a CDP as a transport. From what I can gather, using a CDP as a transport seems to mean that you're basically just using it to read data off of a CD in such a way as to bypass the CDP's own DAC. Is that correct? If so, does the DAC of the CDP matter at all if I'm just going to output the digital signal to an external DAC? I'd appreciate it if someone would elaborate on this point for me.

Additionally, I'm wondering if anyone has any specific opinions regarding the suitability of the Cambridge Audio 540C V2 as a transport for an external DAC. As I noted in my other thread, I'm going to be buying the Keces DA-131.1 in the near future, so any information on that front will be appreciated. If there is a device that is available for roughly the same price that would serve as a better transport, I'd love to hear about it.

Thanks!
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post #2 of 3
9/9/08 at 3:32pm
I'm using a CDP as a transport....

Sony CDP-X5000 top loading CD player... And it works TONS better as a transport, it have lots of potential as transport, but kinda sucks if used as a player. The analog output is tainted with some kind of white noise like stuff, and that's one of the reason that I only use it as a transport. (The primary reason: I BUY this darn thing for the sole intension of using it as a transport...)

One of the things that makes external DAC work better is simply because it is further away from the noisy motors and other components in the player/transport.

Better transport will sound better, that's for sure, but I guess I'll get flamed by all those head-fiers who vigorously defend the idea that all digital sounds the same. Well, the same transport with a little change in the environment would make it sound different, why won't a better transport sound different?


I'm working on something that I'm sure will get me flamed even more, but heck, it works like a charm on my player/transport... Ah well...
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post #3 of 3
9/9/08 at 3:56pm
Some thoughts (courtesy of Stereophile) regarding the topic of why the tranports can sound so different. Please note these are directly from the magazine; I am not endorsing either camp so please don't shoot the messenger

...the jitter's spectral content affects certain sonic aspects differently. Jitter can be randomly distributed in frequency (like white noise), or have most of its energy concentrated at specific frequencies. The jitter's characteristics determine each transport's sound.

...jitter in a digital processor's word clock affects the DAC's sound quality. The word clock is the timing signal that controls when the DAC converts the digital audio samples into an analog output. Timing errors in the clock produce voltage errors in the DAC's analog output signal, degrading the DAC's sonic and technical performance.

...The block diagram shows how transport jitter ends up in the DAC's word clock. The numbered labels correspond to the five jitter sources. The diagram shows why transports and digital interfaces sound different — their jitter directly affects the timing precision of the digital/analog conversion process.



...the "bits is bits" camp rejects this thesis, claiming that transport and interface jitter is completely removed by the DAC's input receiver. They consider the PLL an absolute barrier to jitter. Consequently, they argue, transports, digital interfaces, and CD tweaks can't affect sound quality.

...I conducted a little experiment to test this hypothesis. I measured a digital processor's word-clock jitter (with the Meitner LIM Detector described in Vol.16 No.1) when driven by two different digital sources. One source has low jitter (the PS Audio Lambda transport), and one source has high jitter (the Panasonic SV-3700 professional DAT machine). Fig.2 shows the jitter spectrum of the processor's word clock when driven by the Lambda.



PS Audio Reference Link, DAC word-clock jitter spectrum, DC-20kHz, when driven by PS Audio Lambda CD transport (linear freqeuncy scale, 10dB/vertical/div., 0dB = 1ns.) RMS jitter (400Hz-22kHz) = 145ps.

For contrast, fig.3 is the same processor's jitter spectrum—measured at the DAC with the identical test signal and conditions—but with the high-jitter Panasonic SV-3700 driving the processor. Note the vastly cleaner spectrum and fewer discrete-frequency jitter components when the processor was driven by the Lambda. Moreover, the overall RMS jitter (measured from 400Hz to 22kHz) increased from 145ps with the Lambda transport to a whopping 561ps when driven by the high-jitter SV-3700. Clearly, jitter in the S/PDIF signal driving a digital processor does greatly affect word-clock jitter inside the processor.



PS Audio Reference Link, DAC word-clock jitter spectrum, DC-20kHz, when driven by Panasonic SV-3700 DAT recorder (linear freqeuncy scale, 10dB/vertical/div., 0dB = 1ns.) RMS jitter (400Hz-22kHz) = 561ps.




You can read the rest of it here. Just a jump briefly to the conclusion, some interesting comments which may make cable nay-sayers even angrier - regarding digital cable directionality. Once again, please don't shoot the messenger

There is now no question that jitter in CD transports and digital interfaces affects digital audio sound quality. Not only do different transports and interfaces sound different, they produce varying amounts of jitter and have their own "jitter signatures," seen in the jitter's spectral distribution.

Moreover, we can see that transport jitter goes right through the digital processor's input receiver and affects the amount of jitter at the DAC's word clock—the point where jitter makes an audible difference. If the word-clock timing is different, the sound will be different.

The revelation that digital interconnects and their direction can introduce large differences in measured jitter was quite a shock. The differences heard between digital interconnects—and in their directionality—have now been substantiated by measurement.
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