Network Audio Players/Servers

While Lumin’s U2x is typically deployed as a ‘native’ network bridge it also includes comprehensive up/downsampling as well as LeedH’s proprietary digital volume control [HFN Apr ’23], the latter invoked unless the volume is set to ‘100’ in the Lumin App [see boxout]. Instead of striving for precise steps in level, the LeedH algorithm calculates the best volume coefficient to deliver approximate steps in level (for example –1.2dB, –1.8dB, –3.25dB and –4.08dB in place of –1.0dB, –2.0dB, –3.0dB and –4.0dB, respectively). These non-integer steps are calculated to produce the minimum rounding error and, thus, minimise the DSP overhead. Other server solutions, including the Auralic Aries G2.2 [HFN Feb ’24] and Grimm Audio MU1 [HFN Dec ’20] offer digital filter and upsampling options, but no digital volume. With volume governed elegantly in the digital domain, the U2x may be used as a ‘digital preamp’ directly into an outboard DAC via its galvanically isolated USB-A port.

This is where our testing takes place because any boost in performance offered by the U2x over, say, a conventional NAS or PC/Mac, can only be inferred via a third-party DAC. In this case the host DAC’s USB jitter suppression and/or galvanic isolation is revealed, because a DAC with excellent data recovery or onboard reclocking may not express a significant difference between a poor or excellent digital source... and vice-versa. Driven via the U2x’s USB-A output, a DAC with moderate jitter – iFi Audio’s NEO iDSD [HFN Mar ’21] – showed a near-total suppression of its ±33/66/99Hz sidebands from 550psec to ~10psec [see Graph 1] and a marked reduction in uncorrelated phase noise. Hub-powered DACs typically benefit from a clean +5V PSU and here AudioQuest’s DragonFly [HFN Mar ’14] enjoyed a halving of jitter from 300psec (PC interface) to 124psec. This is not only the best jitter suppression we’ve seen with this classic ‘headphone DAC’ [see Graph 2], but the U2x also brought a significant boost in A-wtd S/N from 89dB to 102.5dB. PM