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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
nicktheknife OP
194 posts
 
One reason I brought up the question of galvanic isolation is that I recently watched a video review of the Chord Qutest by an Australian fella on YouTube.  He claimed to have spoken to the Chord owner or developer (no sure which).  Anyhow, it was emphasized that just a certified usb 2.0 cable be used and NOT an audiophile cable which may be detrimental to the sound.  Something in the Qutest design that doesn't like fancy cables I guess.  I don't have the link but it should be easy to find if anyone's interested. 
That is what got me thinking about GI and cables. 
djones51
4,947 posts
 
Some audiophile cables don't meet the USB 2 certification or haven't  bothered to get them certified. 
kijanki's avatar
kijanki
4,432 posts
 
Yes, electrical noise can enter the DAC but is that really relevant if the DAC has a measure of -120 SINAD from the analog output?
Even if this -120dB SINAD was specified for the USB input signal I'm pretty sure they did not use for this specification a noisy computer with typical USB cable, but rather very quiet custom source (possibly battery operated) and inches long cable.  In addition, according to Benchmark FAQ, jitter effects should be reduced 25dB below noise floor since our ears are extremely sensitive to it.  It is because sidebands, that jitter creates, are not harmonically related to root frequency, hence very audible.
Exact quote:

It can be easily demonstrated that most people have the ability to detect and identify tones which are buried 25 dB or more below white noise (A-Weighted). Therefore, it is important to keep jitter induced side bands nearly 25 dB below the A-Weighted THD+N of the converter, otherwise the jitter may become audible.

and the link:

https://benchmarkmedia.com/blogs/application_notes/12142221-jitter-and-its-effects

djones51
4,947 posts
 
Topping $130 DAC E30 has usb noise in at <-135db, SINAD -112db, USB distribution free range 20 -22 bits 32 tone input at 192 khz. This is attached to dirty USB off a display hub using supplied cable.

Topping D90 comes in with -120.5 SINAD using USB in from computer to XLR out generic cable. Dynamic Range is almost 21bits, 124db channel 1, 123.9db channel 2. 
djones51
4,947 posts
 
Benchmark has very good application notes. I've read most of them their DACs perform very well in reducing USB noise. 
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