Network Audio Players/Servers

While the ND5 XS 2's PCM1791A DAC-based analogue output is simpler in execution than Naim's PCM1792A-based NDX 2 [HFN Sep '18], its digital inputs are processed via the same upsampling/jitter-suppressing 40-bit code. It's so effective there's no significant difference in performance whether data is delivered via S/PDIF, USB-A or (wired) network connections. The fixed analogue output offers a maximum 2.22V from a low 23ohm source impedance (increasing to 190ohm at 20Hz) and incurs a mere 0.0002-0.0095% distortion (20Hz-20kHz, 0dBFs), falling to a minimum of 0.0002-0.00085% over the top 30dB of its dynamic range [see Graph 1, below]. The A-wtd S/N is a few dB behind the NDX 2 at 105.6dB and its low-level linearity is true to ±0.3dB over a 100dB dynamic range (±0.6dB over 110dB).

The response and time domain behaviour of the ND5 XS 2 is entirely determined by Naim's custom brickwall IIR filter which is combined with a gentle 6th-order analogue filter at the output. This digital filter type suffers no pre-ringing, but does exhibit extended post-ringing [see Graph 2, above] and, therefore, no acausal distortion – just like a pure analogue filter. This filter acts earlier than is typical, and trades a reduced attenuation of stopband artefacts immediately adjacent to the top-end of 48kHz music media (just –43.1dB at 26kHz re. 22kHz) while restricting the response of both 96kHz and 192kHz digital audio to a –3dB point of 29kHz. Lower 44.1kHz/48kHz sample rates have an insignificant –0.3dB roll-off at 20kHz. Jitter suppression, meanwhile, is not only superior to that observed with the NDX 2 but defines the current state-of-the-art at <10psec with 48kHz/24-bit inputs and ~15psec at higher sample rates. PM