USB: the lesser of the two evils?

There aren't many points where noise on the USB 5v line can cause a problem. Specifically the 'misuse' of the TAS1020 receiver chip to deliver an asynchronous USB link doesn't seem to cope well with the 5v line and can be noisy unless it is galvanically isolated. So, you need a specific form of non-isolated asynch USB to make it possible to even remotely register a difference that could be detectable.

Put another way, the Arcam rDAC.

I've seen a number of USB cable demonstrations. They all use the Arcam rDAC. Coincidence?
 
Using the TAs1020 fullstop, without isolating the 5v line in the dac it's a recipe for crap. Sinking that to the ground plane with all that switching noise and insufficient decoupling elsewhere in a dac is asking for trouble.

All then Arcam flag wavers will tell you otherwise, "ooh it's the DCS dac in a box" etc, etc. No it isn't, it uses software licensed from DCS and that's it. The DCS uses a FPGA chip not the TAS1020.
 
robertz100 said:
The usb cable was one originally chucked in with a printer, whereas the TOSLINK cable was a decent quality one costing £30+ a metre.

What I meant was I didn't compare the two methods like for like, I think a high quality audio usb cable would have given a fairer comparison. I'd assume the sound would be much better from a usb cable which used high quality silver-plated connectors and oxygen-free copper (probably costs 50x as much as the printer cable).
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sq225917 said:
The 'quality' of a USB cable will make no difference at all. //.. all the fancy construction in the world won't make any difference.

All the online usb cable bullshit stems from the Computer Audiophile site where they would rather waste £1000 on a cable than correctly isolate a £5 one.

Expensive cables are no substitute for good DAC design.
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For once I agree with Simon (more or less), on the point he makes.

Afaic, there is no such thing as "a high quality audio usb cable", in fact there is no such thing as an audio usb cable at all, whether it's high quality one or not. All usb cables simply carry digital data and don't care in the least whether it's audio or not, and neither does the usb bus.

Fwiw, I don't understand the criticism of noise on the usb bus either. It's not something I've had any problem with, on the devices I've used. Most recently being UA25's and RME Firefaces, and AVI equipment. I believe there are several DACs with usb interfaces which don't have noise problems.

JC.
 
FWIW, the M-Audio Fast Track USB dac/adc was recently reported to me by a correspondent (Darren, HDD Audio.net) as being noisy, but I think the noise was likely to be generated internally by that unit itself. - JC
 
jcbrum said:
For once I agree with Simon (more or less), on the point he makes.

Afaic, there is no such thing as "a high quality audio usb cable", in fact there is no such thing as an audio usb cable at all, whether it's high quality one or not. All usb cables simply carry digital data and don't care in the least whether it's audio or not, and neither does the usb bus.

Fwiw, I don't understand the criticism of noise on the usb bus either. It's not something I've had any problem with, on the devices I've used. Most recently being UA25's and RME Firefaces, and AVI equipment. I believe there are several DACs with usb interfaces which don't have noise problems.

JC.
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You don't have the full picture. In 99% of cases, there's no problems as you suggest, but there's a specific problem re. the 5v line on a few (read - Arcam rDAC) DACs that will cause an issue unless you either cut the 5V line (not easy) or shield the line with something more than the cotton sheath the standard cables use.

Most either don't use this receiver chip in this setting, or they use it and galvanically isolate it from the DAC itself. The Arcam happens to be the perfect storm that can make the additional shielding in the cable audible, and it just so happens that every demonstration of USB cables happens to use an Arcam rDAC. Funny that.
 
Yeh, there's a few poorly considered designs out there, half arsed solutions masquerading as the future of audio.
 

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