I don't know.. why do they bother using PCI or USB? Why not just have everything on 1 bus?
I'm not a PC designer... I just know that PCI slots have a lot more pins and that's what all the sound cards use. From what I've heard, USB to spdif converters aren't all that great... which makes sense... since you're changing the nature of the signal from 1 bus to a device output... and the PCI boards do the same thing but generally better.. So, what IS the difference?
PCI and USB are fundamentally two different animals with totally different functions within a PC. PCI, (whose full name is the Peripheral Component Interconnection Local Buss) is a set of specifications defining standards that enable different components within a motherboard to “talk” to each other. These components can either be integrated circuits soldered right onto the motherboard or separate card that the plugged into a connector that has commonly become known as a PCI Slot.
USB (Universal Serial Buss) on the other hand is s specification that was developed to facilitate the connection of external devices to a PC. As opposed to moving data around the inner workings of the PC USB ports were devised as a replacement to the parallel and serial ports that used to be used to connect devices line printers to a PC.
So the two busses serve separate purposes and are not really substitutes for each other. The real question from our standpoint is, what is the best way to interface an external DAC with a PC music server?
In a PCI based solution the digital bit stream is combined with timing information on an expansion card and outputted to the world as a standard s/pdif signal which can then be interfaced with out DAC via a coaxial or optical cable.
In the case of a USB interface the digital data is transported out of the PC to a DAC where the s/pdif conversion is done before the signal is passed off to the D/A section. (This is my impression based on what I have read. There are certainly other AN members with more experience in that area than I and I welcome any comments or corrections from them. Lizard King – any thoughts?) It is interesting to note here that using a USB interface does not avoid the PCI buss as all of the internal communications within the motherboard to deliver the signal to the USB transmitter goes over the PCI buss.
So back to Carl’s original question, which is better? As usual, there is no single answer here because each of the designs involves a number of tradeoffs. The use of a PCI audio card provides a more straight forward data path , but at the same time limits us on the S/P dif side. Most audio cards are designed by computer geeks. Even under the best of circumstances, I would dare say that an audiophiles standard of what constitutes good sound is quite different from the standards of a geek. (Not to mention the difference between what we would be wiling to pay for an audio component vs. what the rest of the human race would consider a reasonable price for a similar functionality.)
In favor of the USB interface, putting the s/pdif processing in the DAC allows that conversation process to be designed and optimized by engineers that not only are used to designing to audiophile standards, but are also likely to have the budget to do what needs to be done. However; the downside of the USB interface is that the digital signal has to go through additional stages of signal processing and protocol conversion leading to the possibility that while the USB DAC might be better equipped to process the digital season, it can be faced with the possibility of getting a lesser quality digital signal to work with right from the start.
So both methods have there own advantages and challenges, each of which is wrapped up with words like “could”, “might” or “in theory”. IMO the whole thing boils down to implementation.. Unfortunately, at this point the only way to know for sure is to set the stuff up and listen for ourselves. Perhaps as more and more people do this and share their experiences her and on other forums like this we will be able to see some patterns emerging and get a better idea of which technology is starting to sound better overall.
But for now, trust only your ears.