CD Player/Transport Reviews

This slightly higher noise floor can be seen in the high-resolution jitter spectrum (fig.6) (footnote 1). The grayed-out trace is the Meridian's noise floor, which is close to the theoretical 16-bit limit; the black trace is that of the BAT, which can be seen to be between 9dB and 13dB higher. I suspect the noise comes from the passive I/V topology used by the BAT player. While this gives better performance in many areas compared with the ubiquitous topology featuring an op-amp chip, the price to pay is an increase in random (thermal) noise.

Fig.6 BAT VK-D5, high-resolution jitter spectrum of analog output signal (11.025kHz at -10dBFS with LSB toggled at 229Hz). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz. Grayed-out spectrum is that of the Meridian 508.24.

The absolute timebase error in the BAT's performance was just +9 parts per million, and its measured jitter level was very low, at 179.5 picoseconds peak-peak. The colored number markers indicate components that the analyzer has identified as jitter. No components can be seen at the fundamental data-related jitter frequency of 229Hz, but there are components visible at the third harmonic of that frequency. These components, marked with a red "1," contribute 74ps to the total jitter figure.

It is important not to make too much of the BAT's slightly higher noise figure. Thermal noise is probably subjectively benign, and the player still has low noise in absolute terms. This is put in perspective by figs.7 and 8, which compare the spectrum of the Miller jitter-test signal when played back on the VK-D5 and Meridian 508.24, respectively. (The analyzer this time was the Audio Precision System One Dual Domain, set to a 1024-point FFT length.)

Fig.7 Spectrum of Miller Audio Research jitter-test signal, reproduced by BAT VK-D5 (linear frequency scale, 20dB/vertical div.).

Fig.8 Spectrum of Miller Audio Research jitter-test signal, reproduced by Meridian 508.24 (linear frequency scale, 20dB/vertical div.).

Finally, it may use tubes, but the BAT offers low distortion. This can be seen in fig.9, which show the player's output spectrum while it reproduces data representing 19kHz and 20kHz tones, each at -6dBFS. The main intermodulation component is the difference tone at 1kHz, which lies just below the -80dBFS mark. This is excellent measured performance.—John Atkinson

Fig.9 BAT VK-D5, HF intermodulation spectrum, DC-22kHz, 19+20kHz at 0dBFS (linear frequency scale, 20dB/vertical div.).

---

Footnote 1: Stereophile used to examine jitter at the DAC's wordclock pin, using the Meitner LIM analyzer. While this produced consistent results, it is the effect of jitter in the analog domain that really matters. To ascertain a CD player's jitter performance, therefore, we have switched to using the Miller Audio Research analyzer. This drives the CD player under test with data representing an 11.025kHz tone at -10dBFS while a 229Hz squarewave toggles the LSBs on and off. A high-resolution FFT analysis—32,768 points, with 64 FFTs averaged—examines the noise floor in the analog domain.—John Atkinson