Simaudio Moon Evolution SuperNova CD player Measurements

Sidebar 3: Measurements

The Simaudio Moon Evolution SuperNova put out a maximum of 4.132V at 1kHz from its balanced jacks, and exactly half that level from the unbalanced jacks, the latter 0.3dB above the CD standard's 2V RMS. Both outputs preserved absolute polarity (ie, were non-inverting), and the source impedance was a low 50 ohms unbalanced, 100 ohms balanced. Error correction was superb, the player not stuttering until the laser-cut gaps in the data spiral on the Pierre Verany Test CD were 2.4mm in length! (When a player has a digital output, I monitor the error-flag bit in the digital datastream for errors, using RME's DIGICheck program. Unusually, DIGICheck indicated that bit 18 in each digital word was set permanently to "On" with CD data.)

Because the SuperNova has a digital input, I was able to test it with external high-resolution data as well as use it to play test CDs. The SuperNova locked successfully to data with sample rates ranging from 32kHz to 96kHz. With 96kHz data, the player's frequency response extended to 45kHz or so (fig.1, top traces above 20kHz), the smooth rolloff continuing the beginning of the top-octave decline seen with CD data (fig.1, middle traces at 20kHz). The CD response dropped to just –0.35dB at 20kHz. Channel matching was superb, but the response with a pre-emphasized CD revealed a broad, 0.75dB-deep trough in the treble (fig.1, bottom traces). Channel separation was also superb, at better than 125dB below 8kHz from both sets of outputs, and was still 115dB at 20kHz.

Fig.1 Simaudio Moon SuperNova, balanced frequency response at –12dBFS into 100k ohms from CD with (middle) and without (bottom) de-emphasis, and with external 96kHz data (top). (Right channel dashed, 0.5dB/vertical div.)

Playing CD data representing a dithered 1kHz tone at –90dBFS, the 1/3-octave audioband spectrum (fig.2, top pair of traces) held no surprises, the traces exactly touching the –90dBFS line at 1kHz, suggesting minimal DAC linearity error. There are also no AC-supply or distortion spuriae evident. In fact, all these traces show is the recorded 16-bit dither noise. Feeding the external data input with 24-bit data representing the same signal, the noise floor dropped by 18dB in the low treble, implying that the SuperNova's DACs actually have 19-bit resolution, which is superb. At lower frequencies, the increased bit depth unmasks some AC noise, but at close to –130dBFS, these are still vanishingly low in level.

Fig.2 Simaudio Moon SuperNova, 1/3-octave spectrum with noise and spuriae of (from top to bottom): dithered 1kHz tone at –90dBFS, 16-bit CD data, 24-bit external data (right channel dashed).

One thing that puzzled me was that when the SuperNova was not playing any signal, the Audio Precision System One still indicated an output of 25mV or so, with a frequency of around 225kHz. To check this out, I performed another 1/3-octave spectral analysis while the SuperNova played data representing a –1LSB DC offset. The resultant spectrum (fig.3) reveals the massive noiseshaping used by the player's DAC chips to achieve the extremely high resolution. It was this noiseshaping that was giving rise to the Audio Precision reading. Some poorly designed amplifiers—though not Simaudio's own, of course—might have problems with the presence of this ultrasonic content.

Fig.3 Simaudio Moon SuperNova, 1/3-octave spectrum with noise and spuriae of –1LSB DC offset, 16-bit CD data (right channel dashed).

The SuperNova's plot of linearity error (fig.4), taken with 16-bit CD data, really shows only the effect of the dither noise used to record the signal. Fed undithered data representing a 1kHz tone at exactly –90.31dBFS, the Simaudio's output waveform was essentially perfect, the three CD voltage levels clearly evident and the waveform offering superb symmetry around the 0V line (fig.5). Fed undithered 24-bit data, the Simaudio's waveform was a pretty good sinewave despite the very low signal level (fig.6).

Fig.4 Simaudio Moon SuperNova, left-channel departure from linearity, 16-bit CD data (2dB/vertical div.).

Fig.5 Simaudio Moon SuperNova, waveform of undithered 1kHz sinewave at –90.31dBFS, 16-bit CD data.

Fig.6 Simaudio Moon SuperNova, waveform of undithered 1kHz sinewave at –90.31dBFS, 24-bit external data.

Harmonic distortion was very low in level. With a full-scale 1kHz tone, the THD levels (true sum of the harmonics) were 0.0007% left and 0.0015% right. The right channel's higher amount, though still very low in absolute terms, was due to a higher level of third-harmonic content, at –97dB (fig.7). The second harmonic was the highest in the left channel, at just –106dB (0.0005%). With a dithered tone at –90dBFS, all the distortion harmonics were buried in the noise floor (fig.8). Intermodulation distortion was also extremely low in level, the second-order difference tone resulting from an equal mix of 19kHz and 20kHz tones lying at –110dB (fig.9)!

Fig.7 Simaudio Moon SuperNova, unbalanced spectrum of 1kHz sinewave at 0dBFS into 4k ohms, DC–10kHz, 16-bit data (linear frequency scale).

Fig.8 Simaudio Moon SuperNova, unbalanced spectrum of 1kHz sinewave at –90dBFS into 4k ohms, DC–10kHz, 16-bit data (linear frequency scale).

I assessed the SuperNova's rejection of word-clock jitter with the Miller Analyzer, which examines the player's output spectrum for sidebands around a high-level tone at exactly one quarter the sample rate. The test signal also includes a low-frequency tone at one 192nd of the sample rate at the LSB level, which, with the 2s-complement data encoding used by CDs, maximally exercises the DAC. The SuperNova's jitter was 424 picoseconds peak–peak, which is low, but not as low as the best players I have assessed (footnote 1). The spectrum of the noise floor (fig.10) reveals that the data-related components are at the residual level, but that most of the measured jitter comes from sidebands at ±711Hz (purple "5" markers) and ±1495Hz (purple "8"). I don't know the cause of these sidebands. Fed external data, the jitter increased slightly, to 484ps.

Fig.9 Simaudio Moon SuperNova, unbalanced HF intermodulation spectrum, 19+20kHz at 0dBFS peak into 4k ohms, 16-bit data (linear frequency scale).

Fig.10 Simaudio Moon SuperNova, high-resolution jitter spectrum of analog output signal (11.025kHz at –6dBFS sampled at 44.1kHz with LSB toggled at 229Hz), 16-bit CD data. Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.

This is superb measured performance for a CD player, especially regarding DAC linearity, low distortion, and error correction.—John Atkinson

Footnote 1: Because of difference in measurement techniques, my measured jitter figures cannot be compared to those specified.—John Atkinson

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