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USB cables and Galvanic Isolation

I've seen that some Dac manufacturers tout having galvanic isolated usb ports.
Does this mean that the Dac is immune to noise/jitter generated by a computer usb port connected to it?
And will a special noise isolating USB cable be required in this instance?
I've seen a lot of threads touting audiophile usb cables and at present I'm not using one.  I am using an Amazon Basics usb cable from my computer to a Peachtree DACitx.  I have been thinking of upgrading the Peachtree as it was my first external Dac which I am happy with but curious as to how much of a jump in SQ I will hear with a newer more expensive DAC. 
Although, I'm not disappointed in the sound I'm getting from the computer, after reading on-line forums that computers generate a lot of noise and mess with the sound I'm a little leary of usb audio.
nicktheknife
kijanki's avatar
kijanki
4,432 posts
 
nicktheknife, If you hear it without signal present, then it cannot be caused by the jitter.  Even with the signal present jitter wouldn't show as one frequency, but as added noise (lack of clarity etc).  It is alway possible that electrical noise injected into DAC by any cable becomes audible when multiple noise frequencies mix on any non-linear element (like transistor or diode) producing lower audible frequency (modulation).  This happens on analog side after D/A conversion.  Since it happens in one channel only it is likely a faulty part (like tube), but finding it might be difficult.  It is also remotely possible that right speaker cable (or speaker) is next to something that induces electrical noise into this channel only.
nicktheknife OP
194 posts
 
@kijanki 
Thanks for the info.  I think it may have been a tube because I haven't heard it since but am keeping my ears open for any further disturbance.  Mostly my computer audio has sound fine.  I've used three different usb cables.  Belkin Gold, Amazon Basics and Monolith.  I can't really make a direct comparison to the three because they are all of different lengths.  They are as follows, 3M, 2M and 1M.

antigrunge2
1,444 posts
 
See the ‘USB sucks’ thread: USB generates an unpredictable set of outcomes depending on the implementation of USB ports of the server and DAC, the quality of the cable and the DAC’s clock as well as the noise environment in the specific setup. As such, galvanic insulation at the DAC is only one requirement for decent sound quality, necessary but not sufficient
kijanki's avatar
kijanki
4,432 posts
 
USB generates an unpredictable set of outcomes depending on the implementation of USB ports of the server and DAC
Asynchronous USB can affect sound only by the fact that it is connected to something, like computer (injecting noise).  The same applies to any other cable supplying digital data.  S/Pdif coax, connected to computer, can be far worse IMHO.  Ethernet might be slightly better, because of galvanic isolation, but still is not perfect.  Even Toslink, that has no electrical connection can make things worse by amplifying existing internal noise (slow edges).

djones51
4,947 posts
 
Look at the measurements on the $199 Schiit Modius. Jitter measures better on USB than coax or toslink. Nothing is perfect but DAC designers are doing a good job with USB. 
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