Meridian Digital Theatre surround-sound music system Measurements 800

Sidebar 3: Measurements Meridian 800

Looking at the Meridian 800's performance as a CD player from its OA20 digital/analog card, its output impedance was a low 47.5 ohms from the single-ended outputs, and almost twice that figure at 94.8 ohms from the balanced XLR jacks. The player didn't invert absolute polarity with the absolute phase set to "+," and the XLRs were wired with pin 2 positive. Although the volume control operates in 1dB steps up to an indicated "99," the analog output stage clipped with a full-scale digital signal when set to "88." All subsequent measurements were performed with the volume set to "87." At this setting, the maximum output level was 7.06V from the balanced outputs, 3.28V from the unbalanced jacks. The well-documented setup program (which runs under Windows 95 and NT) allows the volume control to be disabled. The player then has a fixed maximum output of 4V/2V, balanced/unbalanced.

The 800's frequency response was identical from both sets of outputs, with the bass extending to -0.5dB at 12Hz. However, as shown in fig.1, there is some upper-frequency passband ripple present, which is unusual these days. In addition, the player did not apply the proper de-emphasis when playing a pre-emphasized disc. This can be seen in fig.2, which shows the responses from the unbalanced outputs for both a normal CD (bottom trace above 1kHz) and for a pre-emphasized disc (top above 1kHz). Fortunately, pre-emphasized discs are rare; still, this indicates either a sample fault (I'll check this with the Meridian setup software) or a more general problem.

Fig.1 Meridian 800, balanced frequency response at 0dBFS. (Right channel dashed, 0.5dB/vertical div.)

Fig.2 Meridian 800, unbalanced frequency response at -12dBFS (top below 1kHz) and with preemphasized signal (bottom below 1kHz). (Right channel dashed, 1dB/vertical div.)

The Meridian played 96kHz-encoded DVDs without a problem, but I did find an idiosyncrasy when checking its performance using the Chesky test DVD (CHDVD171): I mentioned above that I left the volume control set to "87" for all the tests, which is just below the analog stage's clipping level. However, while the player performed flawlessly with 44.1kHz- and 48kHz-sampled material at this volume setting, it stumbled when I tried to play 96kHz-sampled squarewaves. The bottom trace in fig.3, for example, is the waveform of a 96kHz-sampled, 12kHz squarewave with the volume set to "85," and has the correct first+third-harmonic shape. (The next harmonic, the fifth, at 60kHz, is above the medium's passband.)

Fig.3 Meridian 800, 12kHz squarewave with volume control at "85" (bottom) and at "87" (top), both with 96kHz-sampled data.

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