Alesis EC-1 A ES/EBU Basic Operation, Selecting AES/EBU I/O Card AS the Digital Source

Appendix E, EC-1 AES/EBU Interface

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 EC-1 card) is installed in the M20. With the EC-1 card installed, pressing the Digital Source button (next to the meter display) toggles through the available sources, such as ADAT OPTICAL, TRACK COPY, and I/O CARD. To select AES/EBU as the digital source, press the Digital Source button until I/O CARD appears in the DIG SOURCE group of the meter display. Now, when Input Select mode is set to digital input for a given channel pair (and dependent on how input routing is configured), an AES/EBU input will be the source for the selected channels.

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 alpha-numeric in the main display will indicate, “AES Clk Source: Chan 1/2”. This implies that the M20 will look for clock input at the channel pair 1 and 2 XLR input. If AES/EBU clock input is not detected, the I/O CARD indicator will flash and the M20’s internal clock will be used until valid AES/EBU input is detected.

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 EC-1 card is the only jack connected to an AES/EBU digital audio source (like a DAT recorder). If no other AES/EBU- synchronous external clock source is available, I/O CARD must be selected as the clock source. But when you do this, the clock source I/O CARD indicator flashes, and audio monitored via the M20 is distorted. Why?

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.

EC-1 MANUAL 1.00 E-7