A DAC will sound it's best when isolated from all sources of noise. In the case of a coaxial signal, optical isolation eliminates galvanic conduction and high frequency noise. Coaxial cables need to be well shielded to prevent their impairment as RF antennae and isolated low noise power supplies (batteries preferred) with AC or DC filters are recommended.
Still to be considered, however, is the potential for a ground loop between the power and signal connections of the DAC. The S/PDIF coaxial signal is bi-phase-mark encoded for an average DC value of zero; however, leakage at the source blocking capacitor or dielectric may introduce DC current flow. Modern DACs use clock re-synchronization to avoid bit-errors from phase noise (jitter); however, jitter does add time-domain distortion to the periodicity of the waveform—another source of DC noise.
DC•ZERO™ stops all this; it's a filter integrated into a BNC adapter that DC isolates the coaxial signal input from the DAC. Zero unwanted DC current flow means better sound. Install one DC•ZERO on a single coaxial 384k connection; install a pair on a dual coaxial 768k connection. The performance of the digital transmission is not affected and the isolation works for all DACs and all sources. With DC•ZERO you will hear more transparency and depth with better delineation of transients and bass notes. When used with integrated DAC+Amps there is also a marked improvement in the control of headphones and efficient loudspeakers.
Orders are being accepted now. DC•ZERO ships in December.