Originally Posted by GuyDebord
In USB and Firewire the digital signal that gets transmitted via serial connections, a 1 and a 0 at a time, therefore, in order to provide error checking, flow control and to synchronize the devices, information is organised in the form of packets and frames. Its not an analogue signal yet, nor a single digital stream, therefore the only purpose the cables need to comply with is to transmit the data packets of 1's and 0's precisely. If a packet doesnt get transmitted precisely, it simply doesnt play it. Its just how it works.
Obviously you don't understand the difference between adaptive and async usb. Very few usb converters use the async method which allow error checking. Most adaptive usb converter stream real time data (audio) and are affected but what is called jitter (like spdif cables).
Line induced jitter (or jitter in digital cables) is a known and measurable phenomenon. Most of the attention has focused on measuring spdif and aes digital cable but the same principle apply for usb cables (on adaptive converters).
Jitter in digital cables can reach high levels as much as a few ns. You can read this research paper (http://www.iet.ntnu.no/courses/fe811...t_audiodac.pdf
) or read this (Stereophile: A Transport of Delight: CD Transport Jitter
Does it mean that line induced jitter is always audible? No, in most systems, it will be barely audible, you need a resolving system to hear the difference between 2 usb cables (when used with an adaptive usb converter). If the dac/amp/headphones are not resolving/revealing enough, a change in the usb cable will probably go unnoticed.
Also, it is better to spend money getting an async usb converter instead of spending one's money in a usb cable.
I hope my answer cleared some misconceptions. I have noticed that too often people confuse the way a hard drive and a usb converter work. While even the cheapest usb hard drive will never drop data nor will it be affected by the quality of the usb cable, it is different for an adaptive converter which are affected by the choice of the usb cable. FYI, more than 90% of the usb chips out there are adaptive and not async. From memory: the PCM270x, PCM290x, CM108, Tenor, ... all of them are adaptive usb and are affected by the jitter from the computer and the usb cable.
Edit -- It is funny how people who say that bits are bits always talk about 1's and 0's. In digital transmission (spdif/usb/...) there are no bunch of zeros and ones running around. What is being transmitted is an electrical square signal wave. That square wave can be affected (rounded off among other things) by the digital cable. What is important is not the data as much as the timing in spdif and adaptive usb.