Appendix E,
BASIC OPERATION
SELECTING AES/EBU (I/O CARD) AS THE DIGITAL SOURCE
When using digital inputs, the Digital Source function selects one of three digital input options. The I/O CARD option will appear in the display only if an I/O card (such as the Alesis
SELECTING AES/EBU (I/O CARD) AS THE CLOCK SOURCE
If a word clock, video, or optical clock source that is synchronous to AES/EBU digital audio input is not available, sample clock for the M20 can be derived from any of the four AES/EBU input channel pairs.
TO SELECT AES/EBU AS THE CLOCK SOURCE:
1.Press the Clock Source button (under the main display) until I/O CARD appears in the CLOCK SOURCE group of the main display.
2.When I/O Card is selected, the
3.To select the AES clock source, use the Up/Down arrows on the keypad. The selections are Chan 1/2, Chan 3/4, Chan 5/6, or Chan 7/8. As noted earlier, if recording multiple AES/EBU pairs, their clocks must be synchronous to avoid “ticks” and “pops” or audio distortion. If you have multiple synchronous inputs (for example, from a single digital mixer), it does not matter which channel pair is chosen as the clock source.
Example: Suppose you set the digital source to I/O CARD, and set the input selection for channels 3 and 4 to digital (shown by the “D” illuminated under those channel meters on the M20). Input 3/4 on the
Because there still is not a valid clock. The M20’s default AES/EBU clock source is channel pair 1/2. But in this example, channel pair 3/4 is the only AES/EBU input present, so the M20 tries to use its internal clock. Since there is no connection between the M20’s internal clock and the internal clock of the DAT feeding it in this case, the numbers that make up the digital transfer are arriving in the wrong positions, causing the distortion. The cure? Simply set the AES clock source to “Chan 3/4" (or whatever channels you’re using), or plug the AES/EBU source into channel pair 1/2.