Will a quality USB cable make a difference....

If you were using itunes on a PC, its no wonder. You will never achieve good SQ this way. You should do more reading on the forums.

Are you now using Kernel Streaming plug-in with Foobar2K on XP or Wasapi on Vista/Win7?

If not, then the same, you will never get it.

What device are you using to get S/PDIF output? Is it a USB DAC? Async USB interface?

Steve N.
Empirical Audio

This is like asking "will a different S/PDIF cable make a difference"

Like with all audio gear, the answer is: It depends.

It depends on the USB interface you are using.

It depends on the rest of your system - is it resolving and low-noise enough to hear the difference?

Everyone believes that they have a super-resolving, low noise system, but IME it simply isnt the case. These types of systems are extremely rare. It takes decades of dedication, tweaking and modding, as well as deep pockets to achieve such a system, and one must have a good ear and patience to avoid going down the garden path along the way. Cables, tubes or the wrong preamp can easily cause one to go down the garden path, regardless of price. Even designers go down the garden path ocassionally.

Steve N.
Empirical Audio

"Hello Steve: Do you mean USB 1.1 versus USB 2.0 or something different."

Certainly async USB protocol using USB 2.0 is better than adaptive mode, but this is not what I'm referring to.

I'm talking about circuit design, implementation and oscillator choice. These are all critical to achieving good performance. Somehow people are under the impression that all Async USB interfaces are alike, just get the cheapest one. This could not be further from the truth. Even after you have a solid circuit design on a schematic, the IC's you use and PC board design are actually critical, as well as the oscillators and power supplies. You can buy $1 oscillators or $200 OCXO oscillators. You can have a 3-terminal regulator or a fast discrete regulator. You generally get what you pay for. Dont expect to pay $100 and get vinyl quality sound. When it comes to digital, this design is even more critical than the DAC itself.

Steve N.
Empirical Audio

"Assuming that you have already USB DAC with async USB protocol - do you need special (async?) protocol for the sender i.e. your USB 2.0 computer port ?"

The computer device driver takes care of this, either native or custom device driver, and the USB port controller hardware in the computer.

"Again, you refer above to the DAC (or USB Adaptor) or to the computer(server) ?"

What I'm talking about is the DAC or converter USB interface design, not the computer.

"Today's fashion is to match cheap computer with expensive and very good USB DACs and I wonder how your comments are related to this fashion."

The cost of the computer is not usually significant. The only requirements are USB 2.0 compliant port and a reasonably fast I/O structure inside. Either of these can be compromised at any price. The latter has been poor on certain PC laptops, including Dells. Mac Mini has very good I/O using USB.

The more critical thing is how the USB interface was designed on your DAC or USB converter. With the advent of async USB interface, the role of the computer is much less significant.

Steve N.
Empirical Audio

"Sorry, but it's just not possible. Keeping it simple, USB is a digital data transport bus, not an analog port. All it moves in the data path is 0s and 1s."

I'm afraid that this is a tired argument. I've read the same argumant dozens of times on the forums. This shows a misunderstanding of the difference in audio streaming and other data transfers.

This is real-time. All other transfers from a computer are not real-time, except maybe some video.

Because it is real-time, it is subject to timing variations. These timing variations can have an impact on the USB interface, ranging from direct jitter affects, power effects, grounding effects, RFI effects and transmission-line effects.

Steve N.
Empirical Audio

"I agree with you about timing variations. There's also latency, packet loss/corruption, and a host of other issues that can affect USB (or any almost any other data connectivity protocol)"

No, I think you missed the point. Its the cycle-to-cycle timing variations, the jitter that sets audio streaming apart from other applications of USB. This is not about missed packets or data errors. These are extremely rare.

"Anyone who wants to can find and read Gordon Rankin's excellent white papers on USB and specifically asynchronous mode operation."

Gordon does understand a lot about the software and protocol aspects of USB. That is his strength IMO.

I, on the other hand have strengths in high-speed digital design, transmission-line effects and other relevant design areas. Gordon is not the only one with async USB interface designs.

I have found that none of these async USB interfaces are completely immune to the benefits of a good USB cable, not Gordons, not mine. I have not discovered the exact mechanisms, but I know its true.

Steve N.
Empirical Audio

"I'm pretty certain he was the first though!"

I believe Ploytec and other Pro Audio designers had async designs out first, resulting in products from EMU and Tascam. I interfaced these to my Pace-Car.

Steve N.
Empirical Audio