Lots of stuff on this in the forums, including very recently.
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If the digital signal is not retrieved from the CD accurately, the DAC will not have a quality product from which to work. People have said over the last 20 years that digital is digital, so it doesn't matter what you use to get the one's and zero's from the disc, but my contention is that this is false. Everything plays a part in the sound.
The quality of transport is the most important part of digital playback. I've tried various combinations of transports and DACs and every single time transports made much bigger difference. If you are investing in digital separates, spend the money on a good transport first, you won't regter it.
Also, if you are mainly interested in CD, get a stand alone redbook transport. Universal players never achieve the same quality in CD as CD only transports do.You can get a great used CD transport for very little money these days.......
I have been trying to decide on a transport for my system and have auditioned several transports in my system recently. I currently have a CAL Delta, a Sony DVP S7000, a CEC TL5100Z, and a Vecteur D2. Each of these units sounds a little different in my system (running through a Scott Nixon TubeDac, a Bottlehead Foreplay preamp and a pair of 2A3 amps).
In some cases, the differences are very slight, but noticeable to me. So, if your system is capable, you may hear differences also.
Probably depends on the specific innards of the DAC you are using. Per a musical fidelity dac review in stereophile, that company's designer (Antony Michalson or something like that)says they reclock the bit stream in the DAC, and so which particular transport or cd player with digital output you use doesn't make diddly for difference.
A DAC which does not reclock might be much more sensitive to variations in timing from a less than perfect signal source.
There are a lot of great used cd players with digital outputs, my suspicion is that a great cd player probably does not have poor bitstream timing and tends to be priced a lot more competitively than a transport. Other thing is it is handy to be able to swap back and forth between the cd player output and the dac output when evaluating your system or when your dac is on the fritz.
Here's what I know: the $30 CD Drive in my computer can read most CDs (except those that are heavily scratched) PERFECTLY (tested via checksums during the ripping process) at speeds up to 52x normal playback speed. If you don't think your audio-quality CD drive can read CDs at 1x playback speed, or some ridiculous liquid you apply to the surface of the CD will somehow make these perfectly read bits sound better, I've got some swamp land in Florida you should definitely think about investing in. :)
It is all about the DAC.
I can not disagree more with Scrith's comments. My findings are that the transport is at least as important as the DAC. It's not about the ones and zeroes, it's about the timing of the ones and zeroes. This is jitter. I updated from a Theta Data Basic to a Basic II and the difference was outstanding. Half a dozen other transports have fed my DAC (Theta Gen Va Balanced) over the past few years and no two have sounded the same. Disclaimer: I bought land, and live, in Florida. So what do I know?
I wonder if the difference in sounds with different transports is sometimes related to how the particular transport is polluting the incoming 120v line? I do get a better sound from my system with a JPS labs digital cable connected to the cd player I'm using as a transport (Arcam alpha 10 cd, MF Tri-Vista 21).
Maybe not, but if somebody wanted to explore the notion, there is some info on audio asylum about the JPS labs being just a basic cable with a simple r/c network in one of the plug casings, and I believe you can buy it from the original manufacturer for less than $50.00 US.
Motors and digital devices are inheritantly nasty polluters.
I didn't say that timing was not important or the total problem. I said as long as the one's and zero's are there. In the case of reclocking the signal it gets more complicated than that. There is a reason we use stratum clocks in the tellecommunications industry at both ends of the signal.
So I will say it again, as long as the one's and zero's are there. Then you get into the checksum software you used to varify the correct reading of the bits. Did it read the bit length?
The transport and the cable can and do make a big difference.
Jeff_jones - No, It is not the AC power "pollution". It is generally the jitter spectrum that varies from one transport to the next and the edge-rate of the S/PDIF signal, as well as the impedance mismatch. I have found lots of transport S/PDIF outputs that are not even remotely matched to 75 ohms characteristic impedance.
I've been reading about modders like Audioengineer(Steve) AKA Empirical audio that have tested some of there modded players before and after a clock upgrade.Their results show the jitter dropped dramaticlly coming out of the S/PDIF output.My guess is it shouldn't be difficult to get a dvd player to perform as well or better than some stand alone transports.
A good DAC will buffer the data stream it is receiving so that the timing from the transport is irrelevant. So the timing will be based on the clock in the DAC, and the assumption that the DAC knows the rate to play the data back at (which, in most cases, is present on the front panel of the DAC as an indicator light or timing readout...e.g. 44K, 48K, etc.).
The only room for error is the transmission of the data stream, which needs to move data at a fraction of the rate that computers routinely send (and receive) digital data (losslessly, I might add, over extremely inexpensive cables).
Steve N - I appreciate your perspective, but I'm guessing that you don't have your DAC, personal computer, and house fan all plugged in to the same power strip. My only point being that when evaluating audio components that are bad about creating electrical hash on the line (Transports), audible differences may be partly due to power quality differences seen by the rest of your system.