Alesis ALESIS M20 owner manual Tutorial 3 Recording Digital Audio from Other Sources, 15-7

Chapter 15, Tutorials and Applications

TUTORIAL 3: RECORDING DIGITAL AUDIO FROM

OTHER SOURCES

Recording digital audio onto the M20 from a source other than an ADAT-compatible device requires a digital audio interface, like the Otari UFC-24 or Kurzweil DMTi, or inserting an Alesis EC-1 AES/EBU interface into the M20’s Expansion Card slot. These convert other digital audio formats to the Alesis Optical format. The ADAT-PCR card can also output audio recorded into a hard disk editing program as ADAT Optical format-compatible signals.

When recording digital audio into the M20 from another ADAT-family device in a multiple ADAT system, the M20 recording the audio is already synchronized with the other machines because all slave machines are automatically set to External Clock mode. They follow the master precisely.

When recording digital audio from some other source, the M20 must synchronize its clock to the incoming digital audio. How this is done depends on whether you are using a single M20 or a multiple ADAT system. We will assume an ADAT Optical interface cable is carrying the incoming digital audio, perhaps from an ADAT-PCR card.

With a single M20, connect the incoming Optical Out (e.g., from the ADAT-PCR card) to the M20’s Digital In using a single fiber optic connector. Press the M20’s Clock Source button, and set its clock source to Optical. The M20 will synchronize to the clock information present in the Optical Out.

In a multiple ADAT system, you have two choices: synchronize the digital audio source to the ADAT system (as described above for a single ADAT), or sync the ADAT system to the digital audio source.

If the source does not have a clock input (i.e., it cannot sync to an external clock), you need to choose the latter option. Connect the Optical Out to the master ADAT’s Optical In, whose Optical Out already connects to the next slave, and so on. Set the master’s Clock Source to ADAT (or I/O card if using the AES/EBU interface). If no digital audio clock is detected, the master M20 will continue using its own internal clock. When the master receives digital audio (and therefore, a digital clock), the master M20 will sync to the incoming digital clock.

DIGITAL CLOCK CONSIDERATIONS

Switching between the M20’s two internal clock sample rates (48 kHz and 44.1 kHz), changes the reference used for computing tape location. Therefore, the same tape location will appear to have two different time addresses depending on the selected sample rate.

Since the M20 cannot detect an external clock’s sample rate, you need to choose the reference base the M20 should use to calculate tape position while syncing to the digital clock. Select either 48 kHz or 44.1 kHz with the Sample Rate button.

If you hear clicks in the audio after recording from a digital source, either the Clock Source is set incorrectly, or there is some other timing problem. Most commonly, clock problems are the result of trying to use SMPTE Chase and receive digital input simultaneously, where the digital source itself is not chasing the same SMPTE or clock reference as the M20, or the SMPTE isn’t referenced to digital clock. There

must be one, and only one clock source in a multi-machine system.

ALESIS M20 REFERENCE MANUAL 1.06 15-7