Outboard DACs

All digital inputs are processed via the same upsampling/jitter-suppressing 40-bit code and pass through the same PCM1792A DAC, a regime that’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 17ohm source impedance that increases to 190ohm at 20Hz. The NDX 2 offers a mere 0.0002-0.0055% distortion (1kHz, 0dBFs to –30dBFs) and 0.00075-0.0035% (20kHz, 0dBFs to –30dBFs) [see Graph 1, below] and a suitably wide 109dB A-wtd S/N ratio that enables a low-level linearity that’s true to ±0.1dB over a 100dB dynamic range (±0.5dB over a 110dB range).

The response and time domain behaviour of the NDX 2’s various digital inputs is entirely determined by Naim’s custom upsampling digital filter [see In-House DSP sidebar]. This filter acts earlier than is typical, providing reduced attenuation of stopband artefacts immediately adjacent to the top-end of 48kHz music media (just –43.6dB at 26kHz re. 22kHz) and restricting the response of both 96kHz and 192kHz digital audio to a –3dB point of 27kHz. Lower 44.1kHz/48kHz sample rates feature a (subjectively insignificant) –0.65dB roll-off at 20kHz while Naim’s dual-mono analogue stage layout ensures that channel separation is >110dB from 20Hz-20kHz.

Jitter suppression is excellent if not absolutely state-of-the-art [see Graph 2] with evidence of very low-rate jitter (note broadened peak) and correlated sidebands at ±384Hz and ±768Hz (65psec with 48kHz/24-bit data) and extending to ±1152Hz, ±1536Hz, etc (105psec with 96kHz/24-bit data). PM

Maximum output level / Impedance: 2.22Vrms / 17-191ohm
A-wtd S/N ratio (S/PDIF / USB): 109.1dB / 109.0dB
Distortion (1kHz, 0dBFs/–30dBFs): 0.00028% / 0.0053%
Distortion & Noise (20kHz, 0dBFs/–30dBFs): 0.0034% / 0.0012%
Freq. resp. (20Hz-20kHz/30kHz): +0.0 to –0.65dB/–15.9dB
Digital jitter (48kHz / 96kHz): 65psec / 105psec
Resolution @ –110dB (S/PDIF / USB): ±0.6dB / ±0.6dB
Power consumption: 16W (1W standby)
Dimensions (WHD) / Weight: 432x87x314mm / 10kg
Price: £4999