Network Audio Players/Servers

As HiFi Rose’s streamer/DAC architecture evolves [see boxout], and its technical performance nibbles away at the limits of measurable noise, distortion, etc, some implementational foibles still persist. Of course, in the ‘real world’ of loudspeakers with distortion x1000 higher and vinyl sources with groove noise at least x100 higher, the RS451’s roster of specs is largely of academic interest. But here goes anyway... The programmable output level ranges from 500mV to 10V (9.8V via the XLR outs, conferring a 122.5dB A-wtd S/N ratio) but all our tests were conducted at the standard 6V (5.84V) setting where distortion holds to a very low 0.00003-0.00013% (re. 20Hz-20kHz) over the top 20dB of its dynamic range [see Graph 1, below, and note expanded 0dB to –140dB scale]. Output impedance is a low, drive-anything <1ohm from 800Hz-20kHz but increases at lower frequencies to 62ohm/100Hz and 875ohm/20Hz. This is typical with capacitor-coupled output stages as is the –0.35dB/5Hz to –1.5dB/2Hz infra-bass roll-off.

However, as experienced with the RS151, the (now) seven digital filters would not reliably load when selected. Most often it defaulted to the fast roll-off minimum phase digital filter which offers a 73dB stopband rejection and flat responses reaching out
to –0.1dB/20kHz, –0.2dB/45kHz and –0.9dB/90kHz with 48kHz, 96kHz and 192kHz media, respectively. Similarly, the very high (~20nsec) low-rate ±2.65Hz jitter seen in earlier HiFi Rose player/DACs persists in this latest model. Higher-rate jitter changes with input, varying from a maximum of 950psec over S/PDIF [red spectrum, Graph 2] to 450psec with local media [black spectrum]. This is clearly linked to the bespoke data routing rather than the choice of DAC chips. PM