Simaudio Moon Evolution Andromeda Reference CD player Measurements
I measured the Simaudio Moon Evolution Andromeda Reference's performance using both our Audio Precision System One and an Audio Precision System SYS2722, the latter on loan from AP (see "As We See It" and Audio Precision's website).
Like Simaudio's single-box SuperNova, reviewed by Wes Phillips in January 2007 (see my measurements), the Andromeda had superb error correction, suffering no glitches in its output with the Pierre Verany test CD until the gaps in the data spiral were more than 2mm in length.
From its unbalanced RCA jacks, the Andromeda's maximum output level was 2.11V, 0.46dB higher than the CD standard's 2V RMS, sourced from an impedance of 50 ohms, as specified. The maximum balanced output was exactly twice that level, sourced from twice the impedance, as expected. The balanced XLRs are wired with pin 2 hot. Both outputs preserved absolute polarity— ie, were non-inverting—when the red front-panel Phase LED was off.
Fed external digital data sampled at 96kHz (fig1, blue trace), the Andromeda's frequency response started to roll off at the top of the audioband and was –3dB at 48kHz, suggesting that the player uses a digital filter optimized for time-domain performance and sound quality at the expense of stop-band attenuation. With 44.1kHz-sampled data, the response rolls off above 14kHz or so (fig.1, red trace; fig.2, top pair of traces). Playing back a CD with pre-emphasized data, the Andromeda displays the same response error as the SuperNova, reaching –1dB in the mid-treble (fig.2, bottom traces). Channel separation (not shown) was superb, at better than 120dB across the band.
Fig.1 Simaudio Moon Andromeda, frequency response into 100k ohms with external data sampled at 96kHz (blue) and 44.1kHz (red). (0.25dB/vertical div.)
Fig.2 Simaudio Moon Andromeda, frequency response into 100k ohms with normal CD data (top) and with pre-emphasized CD data (bottom). (Right channel dashed, 0.5dB/vertical div.)
The fact that it has a digital input allowed me to test the Andromeda with high-resolution data, which revealed that its D/A section is very much better than required by CD data. The top pair of traces in fig.3 show the player's output while it played a dithered tone at –90dBFS, analyzed by a 1/3-octave bandpass filter with its center frequency swept down from 20kHz to 20Hz. The tone peaks at –90dBFS, as expected, and the noise floor is free from harmonic or supply-related spuriae. The noise spectrum is actually that of the dither noise used to encode the signal on the CD. Extending the bit depth to 24 dropped the noise floor by up to 20dB (fig.3, middle traces), implying that the Andromeda has sufficiently low noise to allow a true resolution of better than 19 bits. Certainly it has no problem decoding a tone at –120dBFS (fig.3, bottom traces). Performing an FFT analysis of its output while it decoded the 24-bit, 1kHz tone at –90dBFS gave the spectrum shown in fig.4: minuscule amounts of third and seventh harmonic can be seen, as well as the vestigial amount of 120Hz power-supply noise in the left channel only (blue trace), which could also be seen at a mind-numbingly low –134dB in fig.3.
Fig.3 Simaudio Moon Andromeda, 1/3-octave spectrum with noise and spuriae of dithered 1kHz tone at –90dBFS, 16-bit data (top) and 24-bit data (middle), and of 24-bit dithered tone at –120dBFS (bottom). (Right channel dashed.)
Fig.4 Simaudio Moon Andromeda, FFT-derived spectrum of 1kHz sinewave at –90dBFS, 24-bit data (linear frequency scale; left channel blue, right channel red).
Testing the Simaudio's DAC linearity error with 16-bit data showed only the effect of the recorded dither noise, so I haven't shown the graph. With 24-bit data (fig.5), the error (red trace) was negligible down to the –120dBFS limit of the test. As a result, the Andromeda's reproduction of an undithered 16-bit tone at exactly –90.31dBFS was essentially perfect (fig.6), with excellent waveform symmetry and the three DC voltage levels described by the data clearly evident. The 24-bit waveform at the same signal level (fig.7) was as good as predicted by the spectrum in fig.4.
Fig.5 Simaudio Moon Andromeda, left-channel departure from linearity, 24-bit data (2dB/vertical div.).
Fig.6 Simaudio Moon Andromeda, waveform of undithered 1kHz sinewave at –90.31dBFS, 16-bit data (left channel blue, right channel red).
Fig.7 Simaudio Moon Andromeda, waveform of undithered 1kHz sinewave at –90.31dBFS, 24-bit data (left channel blue, right channel red).
With the highest-level signals, distortion was superbly low (fig.8), with the third harmonic the highest in level, at just –110dB (0.0003%). Some higher-order harmonics can be seen in this graph, but these are extremely low in level. Though the Andromeda's level of intermodulation distortion was also extremely low when tested with an equal mix of 19 and 20kHz tones, the use of the slow reconstruction filter does allow ultrasonic images of these tones to appear at quite a high level (fig.9). In themselves, this behavior should not adversely affect sound quality, but there might be some unpredictable system effects.
Fig.8 Simaudio Moon Andromeda, spectrum of 1kHz sinewave at 0dBFS into 100k ohms (linear frequency scale; left channel blue, right channel red).
Fig.9 Simaudio Moon Andromeda, HF intermodulation spectrum, 19+20kHz at 0dBFS peak into 100k ohms (linear frequency scale; left channel blue, right channel red).
Playing CDs and measured with the Miller Audio Research Jitter Analyzer, the Andromeda offered low levels of word-clock jitter, at 286 picoseconds peak–peak. Fed external data with the worst-case situation—the signal sourced from my PC via 15' of TosLink cable, converted to an electrical coaxial signal with a Sonic Solutions format converter, as the Simaudio has no optical input—the jitter rose to 451ps. The spectrum of the player's output under these conditions is shown in fig.10. The highest-level sideband pair is data-related, lying at 11.025kHz, ±229Hz, though most of the estimated jitter comes from higher-frequency sidebands. Some spreading of the central peak, due to random low-frequency time-base fluctuations, is also evident. The measured jitter level is still fairly low in absolute terms, however.
Fig.10 Simaudio Moon Andromeda, high-resolution jitter spectrum of analog output signal (11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz), 16-bit external data sourced from PC via 15' TosLink and an optical/coaxial data converter. Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz (left channel blue, right channel red).
Overall, this is excellent measured performance, and way better than that required to reproduce CDs. And that digital input allows owners of convenience products like the Slim Devices Squeezebox to take advantage of the Andromeda's excellent DAC and output stage.—John Atkinson