A Case of the Jitters Good enough for CD playback

Test Results 2: Good enough for CD playback

PrimaLuna ProLogue Eight CD player
$2495, reviewed by Fred Kaplan and John Atkinson in July and October 2008.
This tube player's jitter level was a fairly low 406.5ps peak–peak. More significant, the highest-level sidebands that can be seen to either side of the central 11.025kHz tone in fig.9 lie at the power-supply–related frequencies of ±60Hz and ±120Hz. Actual data-related sidebands were much lower in level; if it weren't for the supply-related spuriae, the ProLogue Eight would have very good jitter rejection. While the left channel's noise floor was 3dB below the 16-bit level, the right channel's noise (red trace) was at that limit, implying that the PrimaLuna's resolution is only just sufficient for CD playback.

Fig.9 PrimaLuna Prologue Eight, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz (left channel blue, right red).

Sooloos Media Server System
$10,500, reviewed by Jon Iverson and Kalman Rubinson in September 2008.
The spectral spikes toward the sides of fig.10 are data-related sidebands with frequencies multiples of 229Hz. These are close to the test signal's residual level, but perhaps of more subjective significance are the lower-frequency sidebands that can be seen to either side of the central peak. These are spaced at ±86Hz and its multiples, which may have resulted from the fact that the analog output jacks of our review sample were incorrectly grounded to the chassis. This was due to a manufacturing error and may well have injected noise from the switch-mode power supply into the audio circuitry. Even so, both the noise floor and the calculated jitter level were very low, the latter coming in at just 254ps peak–peak.

Fig.10 Sooloos Media Server, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz (left channel blue, right red).

Krell Evolution 505 SACD/CD player
$10,000, reviewed by Fred Kaplan in September 2008.
Like that of Krell's SACD Standard, which Michael Fremer reviewed in December 2003 (see www.stereophile.com/hirezplayers/1203krell/index5.html), the Evolution 505's noise floor looks double-humped around the fundamental (fig.11), suggesting that some modulation noise is present. As I wrote at that time, low-frequency noise modulation can be audible, but high-frequency effects like this may well be masked both by the music program and by the ear's decreasing sensitivity in this region. The actual jitter level was very low, at 331ps peak–peak, but some spectral spreading of the central tone is apparent, and there also appears to be some suppression of the lower-order data-related sidebands. Something peculiar is going on in the Krell's signal-processing circuitry, at least with PCM data. SACD data are handled differently, I believe.

Fig.11 Krell Evolution 505, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz (left channel blue, right red).

Onkyo DX-7555 CD player
$599, reviewed by Robert Deutsch in January 2008.
Other than the data-related sideband pair at ±230Hz and the power-supply–related sideband pair at ±120Hz, the higher-order harmonics of the low-frequency squarewave in fig.12 are at the residual level, resulting in just 279ps peak–peak of word-clock jitter. Despite the Onkyo's affordable price, it offers excellent audio engineering, with a noise floor considerably lower than that necessary for full-resolution CD playback. Though a very slight double hump can be seen in the shape of the floor to either side of the central spike, I suspect that this will be audibly benign, owing to its low level.

Fig.12 Onkyo DX-7555, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz (left channel blue, right red).

Marantz SA11 Series 2 SACD/CD player
$3500 (review forthcoming).
The Marantz SA-11S2 offered excellent rejection of word-clock jitter, producing just 251ps peak–peak of jitter with the J-Test signal on CD. Narrowband spectral analysis of the noise floor to either side of the 11.025kHz tone (fig.13) indicated that data-related sidebands were almost at the residual level. However, a peculiar rise in the noise floor to either side of the central peak limits ultimate resolution.

Fig.13 Marantz SA11 Series 2, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz (left channel blue, right red).

Cary Audio Design CD 306 SACD Professional Version SACD/CD player
$8000, reviewed by John Atkinson in November 2008.
The Cary demonstrated excellent rejection of word-clock jitter, though the measured level dropped a little as the oversampling ratio was increased. With the CD 306's oversampling set to 384kHz, for example, there was just 246ps peak–peak of jitter—and, as can be seen in fig.14, this was almost entirely data-related, and close to the residual level in the test signal. However, some modulation of the noise floor to either side of the fundamental tone can be seen in this graph; in this respect, the Cary performs very similarly to the Krell Evolution 505, though the spectrum is much closer to pure noise than to discrete tones. This shaping of the noise floor is also almost the inverse of that seen in the Marantz graph. I do wonder if the master clock oscillator is being filtered somehow, in order to reduce the level of lower-frequency random timing uncertainty; nonetheless, the overall resolution seems to be compromised a little.

Fig.14 Cary Audio Design CD 306 SACD Professional, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz (left channel blue, right red).

Shanling MC30
$999, reviewed by Art Dudley in March 2008.
The word-clock jitter of this inexpensive CD-playing integrated amplifier was very low, at 240ps peak–peak, due mainly to a pair of sidebands at ±100Hz (fig.15). The remaining sidebands in this graph are data-related, but are at the residual level of the test signal. The overall noise floor is around 9dB lower than that required for full-resolution CD playback, placing the Shanling at the top of this second group.

Fig.15 Shanling MC30, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz. Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz (left channel blue, right red); cyan and magenta traces show noise floor of perfect CD data.

Ayre CX-7e CD player
$2950, reviewed by John Atkinson in May 2003 and December 2004, Robert Deutsch in February 2006, and Wes Phillips in January 2009.
The Ayre CD player produced just 159ps peak–peak jitter—among the lowest results I have measured, and close to the theoretical limit of the Miller Analyzer. The sidebands visible at the base of fig.16 are, at least as far as the left channel is concerned, actually the residual odd-order harmonics of the low-frequency squarewave. However, two sidebands are visible in the right-channel output at ±229Hz; while these are absent from the left channel, I suspect that they should have been present, but are in antiphase to the residual harmonics at the same frequencies and therefore have canceled them. The CX-7e's noise floor is higher than expected, with the right channel (red trace) being around 4dB worse than the left (blue). I understand that this results from current production of Analog Devices' high-speed, low-settling-time bipolar AD844 op-amp chips being noisier than original samples. (Eight AD844s are used for the CX-7e's direct-coupled analog output stages, and there is no replacement part.) Nevertheless, this is still academic, as both channels are still quieter than the 16-bit quantization floor (cyan and magenta traces).

Fig.16 Ayre CX-7e, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz. Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz (left channel blue, right red); cyan and magenta traces show noise floor of perfect CD data.

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