Asynchronous USB DAC and network streaming (WiFi, Ethernet) have one thing in common - they change "music" to "data" by removing timing. When timing is recreated on the other side of the bridge (or inside USB DAC) computer's speed, amount of RAM etc. become irrelevant (saving money).
Showing 5 responses by kijanki
I'm not sure what is the "Packet Noise" and what it has to do with the quality of the computer (faster computers tend to create more of electrical noise). Computer sends frame of data to DAC every millisecond increasing or decreasing number of samples per frame upon signal coming from the DAC when amount of data in the buffer is below or above certain value (over/under flow control). This data from the computer goes to buffer on digital side of the DAC. Buffered data goes to A/D converter and is clocked at internal DAC clock that is COMPLETELY independent from the computer and the whole transfer operation. This clock should be well isolated from the system noise and if it isn't and becomes jittery then buy another DAC, because this one is poorly executed. |
Yes, you might find some USB port noise sensitivity in some DACs: http://archimago.blogspot.com/2015/05/measurements-usb-hubs-and-8khz-phy.html ..and he finds one DAC in certain setting producing artifacts of noisy USB HUB but the same time he states that he had never seen this before: Okay, to end off... Let me remind everyone one more time that what I'm measuring with the 8kHz noise here is because of the Emotiva XSP-1's sensitivity to noise through the "Home Theater Bypass" input. The 8kHz tone is NOT something I have ever heard / measured coming out of a reputable DAC's analogue outputs! Nor is it something that's found in Stereophile USB DAC measurements. If it were not for this noise sensitivity, I would not even have bothered with looking at ways to attenuate the computer USB noise. Nonetheless, I think this is an interesting real-life demonstration of the noise pollution that can come out of the computer's USB port and a solution that works reasonably well. I did not bother with jitter tests this time as I have never seen the Dunn J-Test change in any substantial fashion with the use of a hub with an asynchronous DAC (see the measurements last time). Think you have a jitter issue? Save up the cash and buy a better asynchronous USB DAC - forget cables and tweak products IMO. Last sentence is exactly what I'm saying. Also look at Stereophile test of, for instance, Ayre QB-9 especially jitter test (Fig. 14). http://www.stereophile.com/content/ayre-acoustics-qb-9-usb-dac-measurements#rgvqgdT0kSAdPz8x.97 It shows no effect of jitter down to -125dB and the only visible jitter artifacts below that are from 120Hz switching noise of linear power supply (120Hz spaced sidebands). This could be fixed by using high quality SMPS. DacMagic behaved poorly in this test. Coupled noise is usually a common mode that can be effectively defeated by even such simple devices like comment mode chokes. You can optimize your system running USB thru quiet Hub (faster computer will make it worse) but the proper thing to do is to find better DAC. |
There is nothing else. If noise floor is low and the jitter is low then it is only matter of quality of the D/A converter and analog output section which is independent of the type of the DAC. It might be possibly lack of jitter since people are used to some noise or distortion and completely without them it sounds analytic, sterile, not engaging. It is pretty much like a difference between clean Jazz guitar and distorted guitar, Distorted always sounds livelier. |