Alesis MasterLink ML-9600 Hard Disk/CD-R Recorder Measurements part 2

Fig.8 shows a similar spectral analysis, performed with 24-bit "digital black" data. Other than the expected rise in the noise floor above 20kHz, due to the oversampling delta-sigma DAC topology, the analog noise floor is as superbly low in level as I expected from fig.7. D/A linearity error (fig.9), assessed using a dithered 16-bit, 500Hz tone, was also negligible down to very low levels, confirming the excellent resolution. The waveform of an undithered tone at exactly -90.31dBFS (fig.10) reveals excellent symmetry and the expected three voltage levels. Increasing the word length to 24 bits gave a very close representation of a sinewave (fig.11).

Fig.8 Alesis MasterLink ML-9600, 1/3-octave spectrum of digital black, with noise and spuriae, 24-bit data (right channel dashed).

Fig.9 Alesis MasterLink ML-9600, D/A left-channel departure from linearity, 16-bit data (2dB/vertical div.).

Fig.10 Alesis MasterLink ML-9600, waveform of undithered 1kHz sinewave at -90.31dBFS, 16-bit data.

Fig.11 Alesis MasterLink ML-9600, waveform of dithered 1kHz sinewave at -90.31dBFS, 24-bit data.

Whether it was harmonic distortion (fig.12) or intermodulation distortion (fig.13), the Alesis' analog output was superbly linear, even into the punishing 600 ohm load.

Fig.12 Alesis MasterLink ML-9600, spectrum of 50Hz sinewave, DC-1kHz, at 0dBFS into 600 ohms (linear frequency scale).

Fig.13 Alesis MasterLink ML-9600, HF intermodulation spectrum, DC-24kHz, 19+20kHz at 0dBFS into 600 ohms (linear frequency scale).

Finally, I used the Miller Audio Research Jitter Analyzer to examine the ML-9600's rejection of word-clock jitter, in conjunction with the diagnostic J-Test signal, which consists of a high-level tone at exactly one quarter the sample rate overlaid with a low-frequency squarewave at the LSB level. The result with the Alesis playing back this signal from a CD-R is shown as the foreground spectrum in fig.14, plotted with high resolution for 3.5kHz on either side of the central 11.025kHz tone.

Fig.14 Alesis MasterLink ML-9600, high-resolution jitter spectrum of unbalanced analog output signal for CD playback (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 internal hard-disk playback of same data.

The calculated jitter level was an extremely low 174.6 picoseconds peak-peak, and consisted primarily of data-related components (identified with red numeric markers) along with a pair of sidebands at ±510Hz (circled purple 3s). However, note the spectral spreading of the central peak, which indicates the presence of low-frequency random jitter, and the contamination of the noise floor with random tones (marked in blue), though it's fair to say that these are very low in level. Peculiarly, when the test was repeated using the same digital data stored on the ML-9600's hard drive, while the measured word-clock jitter remained low in level at 275ps, the level of the spurious noise components increased significantly, as shown by the grayed-out trace in this graph.

Other than this anomaly and the lack of response de-emphasis, the Alesis MasterLink ML-9600 offers state-of-the-art digital performance. Even just five years ago, you would have had to pay tens of thousands of dollars to get this level of measured A/D and D/A performance. To get it thrown in for free—in what would be an extremely versatile, useful, and inexpensive hard-disk recorder even if it had only digital I/O—makes the ML-9600 a superbly engineered bargain. Alesis may have changed ownership, but a product like this demonstrates that the pedigree it acquired with its multi-track digital recorders continues.—John Atkinson

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