Analog source: Grado Statement Reference, The Reference, Benz-Micro LO4 cartridges.
Digital source: Wadia 861, Simaudio Moon Eclipse CD players.Preamplifier: VAC CPA1 Mk.III, Conrad-Johnson Premier 15 phono stage and Premier 17 line stage.
Power amplifiers: Classé CAM-350, Mark Levinson No.20.6, and VTL Ichiban monoblocks, VAC Renaissance 70/70.
Loudspeakers: Magnepan MG3.6/R, Impact Technologies Airfoil 5.2.
Cables: Nirvana SX Ltd., Nordost Valhalla, Synergistic Research Designer's Reference and Resolution Reference, Alpha-Core Micro-Purl, TQ2,…
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Sidebar: Associated Equipment
Not that long ago, digital audio was considered perfect if all the bits could be stored and retrieved without data errors. If the data coming off the disc were the same as what went on the disc, how could there be a sound-quality difference with the same digital/analog converter? This "bits is bits" mentality scoffs at sonic differences between CD transports, digital interfaces, and CD tweaks. Because none of these products or devices affects the pattern of ones and zeros recovered from the disc, any differences must be purely in the listener's imagination. After all, they argued, a copy of…
The block diagram of fig.1 shows how transport jitter ends up in the digital processor's word clock. The call-out numbers in fig.1 correspond to the five jitter sources described above. Fig.1 shows why transports and digital interfaces sound different—their jitter directly affects the timing precision of the digital/analog conversion process.
Fig.1 Jitter sources in a CD playback system
The "bits is bits" camp rejects this thesis, claiming that transport and interface jitter is completely removed by the digital processor's input receiver. They consider the PLL an…
Jitter plots
A typical jitter-measurement plot is shown in fig.4, measured on the highest-jitter source I found: the Panasonic SV-3700 professional DAT machine (a Stereophile-owned sample). The horizontal scale is frequency in Hz, the vertical scale is amplitude in volts. The vertical scale is calibrated so that the "100u" at the bottom is equivalent to 1ps, the "1m" a third of the way up is 10ps, the "10m" point is 100ps, and "0.1" is 1000ps, or one nanosecond (1ns). Note that the vertical amplitude (jitter) scale is logarithmic. Below the "1m" division, each horizontal division equals…
A typical jitter-measurement plot is shown in fig.4, measured on the highest-jitter source I found: the Panasonic SV-3700 professional DAT machine (a Stereophile-owned sample). The horizontal scale is frequency in Hz, the vertical scale is amplitude in volts. The vertical scale is calibrated so that the "100u" at the bottom is equivalent to 1ps, the "1m" a third of the way up is 10ps, the "10m" point is 100ps, and "0.1" is 1000ps, or one nanosecond (1ns). Note that the vertical amplitude (jitter) scale is logarithmic. Below the "1m" division, each horizontal division equals…
After measuring the first two products (the PS Lambda and the Panasonic SV-3700), I went back and repeated my measurements to make sure the analyzer was giving consistent results, and that my test setup was correct. When I remeasured the SV-3700, I got about half the jitter than when I first measured it!
What caused this reduction in measured jitter?
Changing the direction of the digital interconnect between the transport and the jitter analyzer.
This phenomenon was easily repeatable: put the cable in one direction and read the RMS jitter voltage, then reverse the cable…
When I wrote that review, I had no way of measuring transport jitter. Now that we can measure the DTI's effect on jitter, let's see how close our listening impressions were to the DTI's measured performance; it may shed some light on how much jitter is audible and what the sonic effects are.
Fig.11 is the SV-3700's jitter spectrum with the DTI in the S/PDIF signal path. The DTI reduced the jitter by a factor of 10, from 4250ps to 450ps (with a 1kHz, full-scale signal), easily seen in the comparison with fig.4 (the SV-3700's jitter without the DTI). The jitter reduction was less apparent…
Figs.15 and 16 show the Meridian 200 transport's jitter on test signals and music, respectively. The -90dB, 1kHz test signal (the trace with the highest peak at 1kHz) produced a fairly high—but typical—jitter level at 1kHz and 2kHz.
Fig.15 Meridian 200, 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.16 Meridian 200, jitter in S/PDIF data signal, 20Hz-50kHz, when transmitting music #1 (solid) and music #2 (…
Although I haven't yet auditioned it, I measured the gorgeous new $8000 Denon DP-X transport (figs.23 and 24). The DP-X had very low jitter below 200Hz, but slightly higher jitter in the treble. The 2kHz component in the top trace (made with the -90dB, 1kHz test signal) is lower in amplitude than any of the other products tested, but it had more jitter energy above 3kHz when the transport was transmitting a full-scale, 1kHz sinewave. The DP-X had a slightly higher jitter level on music than the best of the transports tested.
Fig.23 Denon DP-X, jitter in S/PDIF data signal, 20Hz-…
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…
Although the No.31 and the $4650 C.E.C. TL 1 appeared to have similar spectra and jitter levels in the graphs presented earlier, we can see in fig.36 that the C.E.C. in fact has lower jitter in the treble, particularly between 3kHz and 40kHz. The No.31, however, has lower jitter and a smoother jitter spectrum in the bass, seen in fig.37. In my listening comparisons of the two products, I noted that the C.E.C. did indeed have a softer, more laid-back treble than the No.31, but that the No.31 had tighter and better-controlled bass. Could these differences in measured jitter performance explain…