Sidebar 3: Measurements
It's difficult to see what measurements would be meaningful with a product like the Roon Nucleus+. However, in his measurements of the Nucleus+ in the May 2018 issue of Hi-Fi News (p.53), Paul Miller reported finding differences in both the absolute levels of jitter and the spectra of the jitter with some USB-connected DACs. I therefore examined the outputs of two of the DACs I had to hand, an original Meridian Explorer and the Ayre Acoustics QX-5 Twenty, while they decoded 16- and 24-bit J-Test data.
I found no differences in the bus-powered Meridian's jitter rejection when it was fed data via USB from my MacBook Pro or from the Nucleus+. The broadening at the base of the spectral spike that represents the high-level tone at one-quarter the sample rate (footnote 1)—due, presumably, to low-frequency random jitter—was identical with both sources. However, the smaller amount of spectral broadening that I'd found with the Ayre QX-5 when fed USB data from the MacBook Pro (fig.1), but not with AES/EBU or Ethernet data (footnote 2), was eliminated when I fed the same data via USB from the Roon to the Ayre. The spectrum (fig.2) was identical to what I obtained with data sourced from the Nucleus+ over my network (fig.3), even though the Roon and Ayre were each connected to my router with 50' of generic CAT-5 cable.—John Atkinson
Footnote 1: See figs. 11 and 12 here. Footnote 2: See fig.12 here.
Fig.1 Ayre Acoustics QX-5 Twenty, Music filter, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz: 16-bit USB data sourced from MacBook Pro (left channel blue, right red). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.
Fig.2 Ayre Acoustics QX-5 Twenty, Music filter, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz: 16-bit USB data sourced from Roon Nucleus+ (left channel blue, right red). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.
Fig.3 Ayre Acoustics QX-5 Twenty, Music filter, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz: 16-bit Ethernet data sourced from Roon Nucleus+ (left channel blue, right red). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.
Footnote 1: See figs. 11 and 12 here. Footnote 2: See fig.12 here.
