Sony SCD-C555ES SACD changer Measurements part 2

Linearity error on CD playback was very low (fig.5), while the spot tones on the test SACD suggested that the linearity error for SACD playback was equally good down to -120dB, below which the exact level was obscured by noise. The 'C555's reproduction from CD of an undithered 1kHz tone at -90.31dBFS was essentially perfect (fig.6).

Fig.5 Sony SCD-C555ES, left-channel departure from linearity, 16-bit CD data (2dB/vertical div.).

Fig.6 Sony SCD-C555ES, waveform of undithered 1kHz sinewave at -90.31dBFS, 16-bit CD data.

The Sony's output stage wasn't fazed by high levels or low load impedances, the distortion harmonics each being below -100dB, or 0.001% (fig.7). And with the punishing HF intermodulation test signal, the analog output was basically free from any distortion products (fig.8).

Fig.7 Sony SCD-C555ES, spectrum of 50Hz sinewave, DC-1kHz, at 0dBFS into 100k ohms (linear frequency scale).

Fig.8 Sony SCD-C555ES, HF intermodulation spectrum, DC-24kHz, 19+20kHz at 0dBFS into 600 ohms (linear frequency scale).

Because the SCD-C555ES will play CD-Rs, I was able to assess its word-clock jitter rejection using the Miller Audio Research analyzer, which uses a test signal stored on a CD-R. The test signal comprises a high-level, high-frequency tone at 11.025kHz, one quarter the CD's 44.1kHz sample rate, over which is overlaid an LSB-level low-frequency (229Hz) squarewave. The analyzer performs a high-resolution FFT analysis of the player's analog-out signal, and searches the FFT bins for symmetrical sideband pairs.

The Sony's jitter spectrum is shown in fig.9. Sidebands at the squarewave frequency and its odd harmonics can readily be seen (red numeric markers), but these are all very low in level. The highest-level sidebands—not that you can call something at -115dBFS "high"—lie at ±500Hz (purple "4" markers, circled in magenta), but I'm not sure what these are due to. Low-frequency sidebands at ±15.6Hz (purple "1," circled in magenta) can also be seen, as can some very low-level spikes at the AC power-supply-related frequencies of ±120Hz (dark blue "2"). Also evident is a spurious tone at 9.47kHz (circled in red, light blue "26").

I don't have the analytic jitter signal stored on SACD. However, Sony's "tentative" test SACD does have a high-level 11.025kHz signal. A spectral analysis of this signal is shown as the grayed-out trace in fig.9. As anticipated from fig.3, the SACD noise floor is a couple of dB lower than that from CD, and while it can't be seen clearly in this graph, the jitter components at ±15.6Hz, ±120Hz, and ±500Hz are present to the same degree as they were for CD playback. Again, there is a noise spike present at 9.47kHz, but with SACD playback, there is also a slightly higher spurious tone at 9.54kHz.

Fig.9 Sony SCD-C555ES, 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. Grayed-out trace is similar analysis for 11.025kHz tone (no LF toggling) from SACD.

As increasingly seems to be the case these days with digital playback components, the Sony SCD-C555ES offers measured performance that is beyond criticism.—John Atkinson

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