High-speed digital transmission is very different from audio frequency signal transmission and requires a different knowledge base and design criteria. Audio cable signal transmission is governed by the principles of inductance, capacitance, and resistance. By contrast, high-speed digital signals are governed by a principle known as ‘transmission line theory’. The performance of a transmission line is governed by the characteristic impedance of the cable. Certain types of cable require a specific characteristic impedance to achieve optimal performance — for instance, cable TV coaxial cables are 75 ohms, while test equipment cables require 50 ohm cables. Modern audio and entertainment systems may have multiple digital connections, each with potentially different characteristic impedances.
While the characteristic impedance is a critical factor in the optimal performance of digital cables, our research also indicates that the precision with which a digital cable is constructed has a significant impact on its performance. Shunyata Research digital cables are produced using a Precision Matched Z concept. This dictates that tolerances of the conductor surface, dielectric extrusion, and the precision of the braided shield are held to smaller variances. To achieve these tight tolerances, the extrusion and braiding machines must be run at one-quarter speed during the manufacturing process. The result is better performance through a reduction of cable-induced ‘signal jitter’.
Superficially, digital cables may look the same as analog cables. For example, a S/PDIF cable can be terminated with RCA connectors, much like analog interconnects. Because the terminations appear the same, analog interconnects could be used as a substitute for a digital cable; but since it has not been designed with the correct characteristic impedance, the performance will suffer.