Naim Audio ND 555/555PS DR Network-Attached DAC Custom Code

Custom Code

The response and time domain behaviour of the ND 555 is entirely determined by Naim's custom 16x upsampling digital filter. This brickwall IIR filter is executed on a 4th-gen SHARC DSP and is combined with two 3rd-order analogue filters (in series to yield a 6th-order roll-off) at the output. This digital filter type suffers no pre-ringing, but does exhibit extended post-ringing [see inset Graph] – akin to a pure analogue filter.


All incoming sample rates are upsampled to one of two elevated base rates – 768kHz (for 48k/96k/192kHz media) and 705.6kHz (for 44.1k/88.2k/176.4kHz media and DSD64 files). The Burr-Brown PCM1704, a legacy 96kHz/24-bit 'ladder type' multibit DAC is used here in current output mode with discrete I-to-V conversion, but its response does not exceed 30kHz with either 96kHz or 192kHz media. Instead, Naim's digital filter cuts in earlier, delivering a 60th-order roll-off at –3dB/27kHz. PM.

Naim Audio Ltd
Supplied by: Naim Audio Ltd
01722 426600