Features

The Proceed PDT (original version) is shown in figs.31 and 32. It had surprisingly low jitter considering how much better the PDT 2 and 3 sound in comparison.

Fig.31 Proceed PDT, jitter in S/PDIF data signal, 20Hz-50kHz, when transmitting digital silence (solid), a 1kHz sinewave at -90dB (dashed), and a 1kHz sinewave at 0dBFS (dotted) (vertical scale, 1ps-2ns, 100µV = 1ps).

Fig.32 Proceed PDT, jitter in S/PDIF data signal, 20Hz-50kHz, when transmitting music #1 (solid) and music #2 (dashed) (vertical scale, 1ps-2ns, 100µV = 1ps).

Finally, we come to the PDT 3 (figs.33 and 34). The much better-sounding 3 (compared to the 1 and 2) actually had higher levels of 1kHz and 2kHz periodic jitter when playing a -90dB, 1kHz sinewave.

Fig.33 Proceed PDT 3, jitter in S/PDIF data signal, 20Hz-50kHz, when transmitting digital silence (solid), a 1kHz sinewave at -90dB (dashed), and a 1kHz sinewave at 0dBFS (dotted) (vertical scale, 1ps-2ns, 100µV = 1ps).

Fig.34 Proceed PDT 3, jitter in S/PDIF data signal, 20Hz-50kHz, when transmitting music #1 (solid) and music #2 (dashed) (vertical scale, 1ps-2ns, 100µV = 1ps).

Incidentally, the jitter analyzer wouldn't lock to the Runco/MSB laserdisc player, the Museatex CD-Deck, or the Meitner IDAT when I attempted to use the latter's digital input/output (which has the jitter-reducing C-Lock receiver and transmitter circuits) as a jitter-reduction device. (These transports' output carrier frequencies were probably shifted from the tolerance allowed in the S/PDIF interface.)

Analysis
Although we can't quantify a CD transport's musical performance just by looking at these curves, some broad correlations with sound quality emerged. The four transports held in highest sonic regard (the No.31, C.E.C. TL 1, Lambda, and Proceed PDT 3) all had low jitter. The Meridian 200, one step lower in "Recommended Components," had higher jitter than all the Class A and B transports that I measured. The JVC XLZ-1010 (replaced in Class D by the similar XLZ-1050) had higher jitter still. Further, I thought the PS Audio Lambda was slightly better-sounding than the PDT 3—and the Lambda had slightly lower jitter. Finally, the Audio Alchemy DTI's effect on jitter—whether an increase or decrease—was clearly audible.

After examining the data and relating the measured results to my listening impressions of transports I was familiar with, I concluded that the data's graphical presentation doesn't have fine enough resolution to show small differences in jitter. Moreover, I'm led to believe by some respected engineers that sound quality is affected even by the very small differences in jitter performance revealed by these measurements. These differences aren't resolved by the graph's vertical scale, which was chosen to accommodate the very high jitter from the Panasonic SV-3700's S/PDIF output.

I've therefore examined the differences between well-known transports by using finer resolution in the graphical presentation. Fig.35 is a comparison of the $1695 Meridian 200 with the $8495 Mark Levinson No.31, shown with an expanded amplitude scale. The Meridian is the solid line, the No.31 the dotted line. The No.31 has a much smoother spectrum—the jitter is more random in nature—and is lower in level overall except in the 100Hz-600Hz band. The Meridian 200's spectrum is spikier, indicating that the jitter is more periodic than random. Remember, random jitter is much more sonically benign than periodic jitter. Random jitter raises the noise floor; periodic jitter creates discrete tones around the signal frequency. These tones, harmonically unrelated to the musical signal, add unpleasant artifacts to the music. Is the 200's spikier spectrum sonically significant? Or are these differences meaningless when we consider the variables involved in a transport driving different processors?

Fig.35 Meridian 200 (solid) and Mark Levinson No.31 (dotted), jitter in S/PDIF data signal, 20Hz-50kHz (vertical scale, 3-20ps, 100µV = 1ps).