Network Audio Players/Servers

Grimm’s designers have engineered +8dB of headroom into the MU2’s output so while 3.03V is available at the 0.0dB volume setting, the maximum balanced output is 6.01V at ‘+6.0dB’ beyond which it clips with peak (0dBFs) digital inputs. To ensure there is no intersample clipping with incorrectly/poorly normalised digital files I would recommend setting the MU2’s volume no higher than 0.0dB. The technical performance of the MU2 is state-of-the-art in respect of distortion and jitter suppression [5psec with all sample rates/all inputs and with no observable phase noise – see Graph 2] but there is ‘character’ in the form of Grimm’s custom digital filter, this 128fs upsampling/truncating/noise-shaping filter adopting a very high tap linear-phase model. We saw a 4fs version in the MU1 [HFN Dec ’20], revealing the extended pre/post ripples, and an advanced version is embedded here, trading temporal distortion (acuasal ripples being a digital artifice) for a superb >135dB stopband rejection and responses flat to 0.0dB/20kHz, –0.3dB/45kHz and –6.8dB/90kHz with 48kHz, 96kHz and 192kHz files, respectively.

Distortion is a very low 0.00003-0.00015% (re. 20Hz-20kHz) with peak level digital inputs [see Graph 1, below] and falls to an infinitesimally low 0.00003-0.0001% over the top 20dB of its dynamic range. The 109dB A-wtd S/N ratio is wide but not record-breaking – a function of the extra gain in the analogue output – but low-level resolution is still excellent as the MU2’s custom DAC is good to ±0.3dB over a full 110dB dynamic range. The XLR outputs have a modest 46ohm source impedance and, while I have already mentioned the flat HF responses, the MU2 also has a subtle bass uplift starting below 40Hz and reaching +0.07dB from 20Hz down to 5Hz. Audible? Unlikely! PM