Network Audio Players/Servers

With in-house hardware and software engineering on tap, the South Korean Citech Company is rightly proud of the performance of its RS150 network streamer. The 'industry leading' measurements certainly illustrate what can be achieved with AKM's AK4499EQ DAC from its vanishingly low distortion that falls to just 0.00005% over the top 30dB of its dynamic range [see Graph 1, below] to its very wide 119dB S/N ratio that assists in delivering the RS150's excellent low-level resolution – good to within ±0.1dB over a full 110dB dynamic range. The maximum 8.65V balanced output is more than sufficient to drive any power amp into clipping without the services of an intermediate preamp and although the ~560ohm source impedance is a little higher than expected other 'analogue' parameters, like the stupendous 145dB channel separation, are testament to the generally very solid production engineering.

There is, however, one fly currently stirred into the digital ointment – a very low-rate ±6.25Hz jitter that extends out some 200Hz [see zoom jitter plot, Graph 2]. This is specific to the RS150 (it does not appear in other implementations of the AK4499EQ), possibly an intermodulation between internal clocks. While numerically very high at >20nsec, experience suggests this may bring a marginal softening to stereo images and top-end 'air'. Of equal subjective impact, perhaps, is HiFi Rose's choice of slow roll-off minimum phase digital filter. This trades zero pre-ringing and limited post-ringing for poor stopband rejection at low sample rates (just 5.4dB at 48kHz) and roll-offs of –3.5dB/20kHz, –6.6dB/45kHz and –8.5dB/90kHz with 48kHz, 96kHz and 192kHz media. This choice of filter is a very good compromise for higher sample rate files (above 48kHz). PM