best way to connect DAC Magic to PC- digital co-ax or USB?

[knacker]

what is best way for sound to connect my pc to DM as I can use either digital co-axial or USB as I can connect via soundcard or USB direct?

My files are all CDs ripped into apple lossless but am also starting d/l from itunes as well- any advice about settings for that will also be gratefully received.

 

[Anonymous]

USB downside: limited to 16b/44, but all CDs are 16b max so no real issue there. Plus: it bypasses soundcard.

Coax: Sound goes through soundcard still, albeit digitally.

I'd go with USB - cheaper cable too. I got a 5m Belkin pro-series cable for £7.

Re: itunes - see these

http://extra.benchmarkmedia.com/wiki/index.php/Windows_Vista_Audio_Playback_-_Setup_Guide

http://extra.benchmarkmedia.com/wiki/index.php/ITunes-QuickTime_for_Windows_-_Setup_Guide

Better yet, download free Foobar 2k and WASAPI plugin (Wasapi only works on Vista). What OS do you use?

 

[knacker]

Vista currently

 

[Anonymous]

Yeah - USB, foobar with WASAPI plugin is the way to go then IMO. Bitperfect output.

 

[knacker]

So Foobar will give a better sound than Itunes?

 

[Anonymous]

It can do. Window mixes all the other sounds your computer makes and re-samples the lot to 48kHz, so your 44.1kHz lossless music is no longer bit-perfect. you can get plugins for foobar that get around it, whereas you can't for iTunes. see here

 

[Anonymous]

USB is a very poor interface
for audio. In theory it looks good, but in practice
it is seriously lacking. The theory is that USB, being asynchronous and
buffered, the DAC can ask the computer for data. This allows the DAC
clock to be the only clock needed. Computers don't like DAC's asking so frequently for
data over the USB bus. USB is not that stable and was not
designed for such applications. The result is a more single direction
feed from the computer causing a lot of jitter. It can also introduce problems with grounding etc.

 

[knacker]

Anyone else confirm this or again just another opinion

 

[Anonymous]

This is what I've picked up from reading about the technical aspects, but corrections are welcome. It is probably true that USB was not designed with audio in mind, and to produce a jitter free signal with a precise time base. But it is not so that if you play at 44.1 kHz that the USB is expected to send 16 bits of data at exactly this frequency. But this is irrelevant since the usb speed is a couple of orders of magnitude higher than required for audio, and the stream is buffered. A proper DAC in a USB sound card should read the data from the USB stream buffer and use its own clock to create a jitter free (upsampled) signal that it then converts to analog. Obviously, if the data run out because the computer is occupied you will get a very noticible dropout. This should normally not happen, because the USB feed has a very high priority in the PC system architecture. However, poorly written other drivers may lock up the computer for many milliseconds - this can be tested (see my other thread). USB sharing also might cause a problem, especially with a hub with several connections, and an agressive other device connected to the same hub. My conclusion: jitter is not a problem with proper (external) HQ components, dropouts neither if the system is configured / fine tuned adequately. Whether co-ax is still better I do not know, I am not sure if the external DAC reclocks the signal from optical or coax digital sources. If so, I see no fundamental difference between USB and S/PDIF. If not the quality of the sound card's digital out circuitry (with/without jitter) might determine the result, and potentially the digital way could even be worse that the better buffered USB stream. BTW, setting up a PC with the proper USB ASIO drivers is much more hassle than just plugging the digital signal of a sound card into the DAC.

Now for a personal test: I have no experience with digital (laptop does not have S/PDIF) , only via USB, but it works great. Very difficult to my ears to hear a significant difference between source (24/192 DAC in CD player Philips SA963) and FLAC (24/192 in external V-DAC) in a ABX setup.

Pete10