USB printer cable VS USB audiophile grade cable?

There are a number of possible explanations that occur to me:

1)Electrical noise that may be transmitted from the computer to the DAC via the cable could to some degree couple "around" the DAC's buffer memory and jitter rejection circuitry (via grounds, stray capacitances in the circuits, etc.), and thereby affect jitter at the point of D/A conversion. The bandwidth and impedance characteristics of the cable will affect the amount and the frequency content of that noise.

2)Some of that noise may result from groundloop effects between the computer and the DAC, which in turn will be affected by the resistance and inductance of the ground conductor within the cable.

3)USB signals have substantial content at RF frequencies. The quality and characteristics of the shielding in different cables may result in differences in radiation of electrical noise from the cable into unrelated parts of the system (including cables and power cords as well as components), which may be sensitive to that noise to varying degrees at various frequencies. The sonic consequences of that can be expected to be arbitrary and unpredictable. The fact that your cable, or at least the previous Belden cable, is or was 12 feet long perhaps increases the likelihood of those effects.

4)Earlier Benchmark DAC's employed an Asynchronous Sample Rate Conversion (ASRC) approach to jitter reduction, which I understand is a technology that is not always 100% bit perfect when faced with significant amounts of jitter on the incoming signal. I suspect that is not applicable to the more recent DAC2 HGC model you are using, but perhaps it too is not 100% bit perfect under some circumstances?

I would add, however, that IMO none of this necessarily suggests that a high degree of correlation between performance and price should be expected among the various audiophile-oriented cables that are available. It also does not suggest any reason to expect a high degree of consistency between the sonic results provided by a given upgraded cable when used in different systems.

Regards,
-- Al

I would think that bits would arrive cleaner by having a sort of wall between the noisy multi purpose computer and the dac. Optical i would have thought would provide this vs a usb which relies on an electric signal from the computer.

Yes, that is a potential advantage of an optical connection. However what you have found, at least in your setup, is that the potential disadvantages of an optical connection outweigh that potential advantage.

One potential disadvantage, I believe, is that the electrical outputs of optical-to-electrical transducers tend to have slow risetimes and falltimes (i.e., slow transitions between their higher voltage and lower voltage states, and vice versa), which can adversely affect the jitter performance of the subsequent circuitry in the DAC. Also, my understanding is that waveform quality, and ultimately jitter, can often be adversely affected by the quality, or lack thereof, of many optical cables.

It is telling that in S/PDIF applications, where digital signals are conveyed from a transport to a DAC, coax connections seem to be preferred by most audiophiles to optical connections.

Regards,
-- Al