Network Audio Players/Servers

Tested in its fixed, maximum line output guise, the Pro Plus offers a standard 2V from a usefully low, cable-agnostic 10ohm source impedance. The A-wtd S/N ratio is a deeply impressive 109dB via all digital inputs while low-level resolution is true to within ±0.1dB over a massive 110dB dynamic range. These are figures more commonly associated with superior outboard DACs at 10x the price (and then some) while distortion is as low as we've seen from any digital device at any price - 0.00005-0.0006% at peak (0dBFs) output from 20Hz-20kHz. Vector-averaging reveals the lowest distortion of 0.00003-0.0003% is achieved at -10dBFs, far lower than WiiM's own conservative specification and requiring an adjusted 0 to -140dB scale on Graph 1, below. This is testament not only to the performance of the AK4493SEQ DAC but also WiiM's own analogue output stage which maintains a >130dB channel separation through the midrange. Arguably, these figures are of academic interest only (but still interesting!). Only the jitter spectrum [see Graph 2] reveals a slight chink in the Pro Plus's armour for while correlated sidebands amount to a mere <20psec (all sample rates with 24-bit data), the slight broadening of the signal peak suggests the presence of a very low-level uncorrelated jitter/phase noise.

AKM's AK4493SEQ DAC includes six optional digital filters with the 'Sharp' linear and minimum phase choices offering the best (69dB) stopband rejection and flattest -0.01dB/20kHz, -0.7dB/45kHz and -2.5dB/90kHz responses with 48kHz, 96kHz and 192kHz media, respectively. The remaining filters have a poorer stopband rejection and a greater HF roll-off, all traded for reduced time domain distortion. 'Super Slow/NOS' - essentially no filter at all - is best suited to higher sample rate media. PM

Above: THD vs. 48kHz/24-bit digital signal level over a 120dB dynamic range (1kHz, black; 20kHz, blue)

Above: High resolution 48kHz/24-bit jitter spectrum with markers. Some low-rate phase noise evident