Alesis ALESIS M20 TUTORIAL 3: RECORDING DIGITAL AUDIO FROM OTHER SOURCES

Chapter 15, Tutorials and Applications

TUTORIAL 3: RECORDING DIGITAL AUDIO FROMOTHER 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.

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.