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Need sound card and external DAC recommendations!

499 views 7 replies 4 participants last post by  thomaspf 
My recommendation would be to forget about a PCI card and get an external box with it's own power supply that connects to your computer via USB or 1394. ATX supplies don't provide the cleanest power in the world. Additionally, there's a lot of stuff going on inside your computer chassis with all the digital circuitry, fans, etc which don't make for a clean environment for the sensitive PLL's and other clocking circuits required in digital audio. Even if you use digital I/O, the soundcard will either have to generate or slave to a sample clock. A 1394 or USB connection moves all the sensitive stuff outside the computer. USB audio devices are pretty common.
 
It's a free country. You're free to disagree. But I've worked directly on this stuff, and what I'm saying is not an opinion.


Yes, PCI cards are designed to operate in a PC chassis... obviously. But running high quality digital or analog audio inside a PC was not in anyone's mind even 10 years ago, not to mention when the PCI bus or the first PC's were devleoped.


In all but maybe the cheap soundcards (which will try to save money by using an existing clock, rather than adding their own), the FSB has no bearing on the word & bit clocks used for sample clocking. And those that do use the PC's clock might even be doing some sleezy sample -rate conversion to compensate for the difference in timing, since digital audio needs a clock that is a multiple of the sample rate. Either they don't even have a PLL to generate the divided down clock or they are only generating a multiple of one sample rate (44.1KHz for example). On good cards/interfaces, you'll find a 256x or 512x crystal oscillator on board. Actually there should be two. One which is a multiple of 44.1KHz, and the other 48KHz


Any device which has a S/PDIF input connection contains a PLL. One is built into any and all digital audio receivers. S/PDIF and AES send clocking information embedded in the bi-phase (aka Manchester) encoded bit-stream. A receiver which is slaving to the incoming clock must phase-lock to this signal and derive a local clock to clock in samples properly. If the device is the clock master, then the PLL is not used but it's still there. Again, only the cheap soundcards will try to use the PC's existing clock.


M-Audio makes pretty decent products, I agree. They're not the best you can get, but certainly a great bang for the buck.



Also, this quote is from the M-Audio website...


"Audiophile USB is the affordable, no-hassle USB audio and MIDI interface for Mac and PC....... delivering 24-bit/96k quality with great dynamic range and noise specs. That’s because it uses AC-powered components that deliver better fidelity than bus-powered circuitry."
 
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