Meridian & Sonic Frontiers jitter bugs: I mentioned that reclocking the CardDeluxe's S/PDIF output with a Meridian 518 solved the mute problem with the Musical Fidelity. Inserting into the datastream the Meridian, which uses the Crystal CS8412 data receiver with a double PLL clock-extraction circuit, produced the grayed-out trace in fig.1. (I used a 2m length of original Illuminati S/PDIF to connect the Meridian to the X-24K.) The noise floor remains high for 500Hz to either side of the central peak, but then rgw individual bins rapidly drop to around -129dBFS, which is the Musical Fidelity's intrinsic background level. The absolute jitter level is only reduced to 984ps mainly because, while the Meridian significantly reduces the levels of the higher-frequency jitter sidebands, the strongest sidebands (at ±229Hz, indicated with red numeric "2" markers) remain as strong as they were without the Meridian at 882ps. In addition, a pair of sidebands appears at ±81Hz.

Soundwise, there was no doubt that the Meridian cleaned up the CardDeluxe's digital output, minimizing a sense of treble grain and enlarging the perceived soundstage.

For interest's sake, I dug out the sample I had bought some years back of the long-discontinued Sonic Frontiers UltraJitterbug, which uses the UltraAnalog data receiver. Again I interposed the unit between the CardDeluxe's data output and the Musical Fidelity X-24K and looked at the jitter-related products in the latter's analog output. The result is shown in fig.2. The noise floor drops across the band to -129dBFS, but surprisingly, the measured jitter rises from 1199ps to 1529ps. Partly this is because some low-frequency sidebands appear (at ±31.2Hz, ±60Hz, and ±180Hz)—or, more likely, are unmasked by the drop in the noise floor. However, this increase in jitter is predominantly due to a significant rise in the levels of the lowest-frequency data-related sidebands, even though the higher-frequency sidebands have been attenuated by the UltraJitterbug.

Fig.2 Musical Fidelity X-24K driven by CardDeluxe via Sonic Frontiers UltraJitterbug, 1m of AudioQuest Digi Pro S/PDIF link, and 2m of Illuminati S/PDIF cable, high-resolution jitter spectrum of analog output signal (11.025kHz at -6dBFS with LSB toggled at 229Hz). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.

I could certainly hear a difference between the output of the Musical Fidelity with and without the Sonic Frontiers—there was mostly silence without it—but I thought the Meridian did the better job of maximizing the sound quality of the X-24K when fed by the CardDeluxe.

Final Thoughts: The fact that the other three D/A processors I had on hand had no problems with the CardDeluxe's S/PDIF output implies that the Musical Fidelity is unusually sensitive to the quality of the S/PDIF datastream feeding it—at least at 44.1kHz. But the fact that the TosLink optical data output of the RME soundcard reviewed this month was by far the cleanest with respect to jitter strongly suggests that, to maximize sound quality from soundcards, the hostile environment of the host PC is best kept electrically isolated from downstream audio components.

In my original review, I had mentioned having suffered from occasional dropouts with the inexpensive hard drives I was using with the CardDeluxe, and conjectured that this was due to bandwidth limitations when reading and writing the enormous amount of data from and to the drives. A number of readers, including Digital Audio Labs' Al Pickard, e-mailed me to say that the problem was more likely due to the fact that regular computer drives periodically perform what is called "thermal recalibration." This is not an issue with computer data files, where the host PC can simply wait; but with streamed data, like music, you get glitches. The only solution is to use certified "audio/video" drives, which can perform extended write and read operations without thermal recalibration. However, these drives are significantly more expensive than what you can buy at Office Depot. (I can recommend the A/V drives sold by Glyph Technologies.)

Overall, my continued experience of the CardDeluxe impresses me with how much high-performance audio engineering is packed into its tiny frame.—John Atkinson