Digital Processor Reviews

Most of the measurements of the MSB were performed using the Audio Precision System One's S/PDIF output set to a 44.1kHz sample rate. However, I also spotchecked the unit's behavior at the higher sample rates using a dCS 904 A/D converter to digitize the System One's analog output, and a Sonic Solutions Optical Converter to translate the dCS's AES/EBU electrical output to the double-speed TosLink S/PDIF format.

The maximum output level was 2.45V, 1.75dB above the standard 2V output. This was delivered from a moderate 215 ohm output impedance. The MSB's analog outputs were noninverting. Channel separation (fig.1) was superb.

Fig.1 MSB Link, crosstalk (10dB/vertical div., R-L dashed).

Using CD, the MSB Link's frequency response (fig.2, upper traces) was flat over most of the audioband, but with a 0.4dB rise at 10Hz and a 0.5dB droop at 20kHz. The response with de-emphasis (lower traces) was identical. Fig.3 is plotted over a much wider range and shows the Link's response at -10dBFS, taken with the dCS A/D converter operating at (from left to right) 32kHz, 44.1kHz, 48kHz, 88.2kHz, and 96kHz. (The ADC's own departure from a flat response is therefore included in the result.) The responses at the two higher pairs of sampling frequencies doesn't differ appreciably in bandwidth; ie, 48kHz doesn't give a wider window than 44.1kHz. But it can be seen that 88.2k/96k operation gives a response that extends out to 40kHz, not quite half the sample rate but still almost an octave greater analog bandwidth.

Fig.2 MSB Link, frequency response at 0dBFS without de-emphasis (top) and with (bottom) (right channel dashed, 0.5dB/vertical div.).

Fig.3 MSB Link, frequency response at 0dBFS with (from left to right): 32kHz, 44.1kHz, 48kHz, 88.2kHz, & 96kHz sample rates (right channel dashed, 5dB/vertical div.).