Accuphase DP-100 Super Audio CD transport & DC-101 Digital Processor Measurements

Sidebar 3: Measurements

Looking first at the Accuphase DC-101's measured performance playing back CDs, its maximum output level was 2.465V unbalanced, 2.46dB balanced, both figures approximately 1.8dB above the CD Standard level. The analog output was sourced from a low 47 ohms from both sets of outputs. While the unbalanced outputs didn't invert absolute signal polarity, the balanced outputs did so, the XLR jacks being wired with pin 3 positive (the opposite of the AES-recommended convention). Setting the DC-101's rear-panel switch to "inverting" actually restored absolute polarity. While the DP-100's error correction for CD replay was good, the transport coping with gaps in the data spiral up to 1.5mm in length without audible glitches, it was not up to the standard set by the latest DVD-mechanism-based players I have tested.

All of the following measurements were taken from the balanced outputs. Fig.1 shows CD-replay frequency response (top traces) and the de-emphasis response (bottom traces). The output is flat within the audioband, and any de-emphasis error is negligible. Channel separation (not shown) was simply astounding, at better than 130dB through the bass and midrange, and still superb at around 120dB at 20kHz.

Fig.1 Accuphase DC-101, CD data, frequency response at -12dBFS, without emphasis (top) and with emphasis (bottom). (Right channel dashed, 0.5dB/vertical div.)

Fig.2 shows a 1/3-octave spectral analysis of the DC-101's analog output while the processor decoded data representing a dithered 1kHz tone at -90dBFS, with both 16-bit CD data (top) and 24-bit data (bottom). The improvement in dynamic range due to the increased word length is around 18dB (ie, three bits' worth), while the noise floor in the lower midrange is one of the lowest I have ever measured. This can also be seen in fig.3, which shows similar spectral analyses performed with the Accuphase decoding "digital black." The analysis in this graph extends to 200kHz, and the plot is free from ultrasonic noise and spuriae, at least with PCM data (see later).

Fig.2 Accuphase DC-101, CD data, 1/3-octave spectrum of dithered 1kHz tone at -90dBFS, with noise and spuriae, 16-bit (top) and 24-bit (bottom) data (right channel dashed).

Fig.3 Accuphase DC-101, CD data, 1/3-octave spectrum of "digital black" with noise and spuriae, 16-bit (top) and 24-bit (bottom) data (right channel dashed).

Examining the DC-101's linearity error with dithered CD data gave the plot of fig.4. The error remains below 2dB down to a superb -117dBFS. As a result of the excellent linearity and high dynamic range, the Accuphase's reproduction of an undithered 1kHz sinewave at -90.31dBFS (fig.5) was essentially perfect. Increasing the bit depth to 24 bits (fig.6) gave a pretty good facsimile of a sinewave at this very low level.

Fig.4 Accuphase DC-101, departure from linearity, 16-bit data (2dB/vertical div., right channel dashed).

Fig.5 Accuphase DC-101, waveform of undithered 1kHz sinewave at -90.31dBFS, 16-bit PCM data.

Fig.5 Accuphase DC-101, waveform of undithered 1kHz sinewave at -90.31dBFS, 16-bit PCM data.

US distributor: Axiss Distribution
17800 South Main Street, Suite 109
Gardena, CA 90248
(310) 329-0187