Alesis ALESIS M20 Synchronization Overview, Synchronization Basics, Chapter, Master or SLAVE?

CHAPTER 16

M20 SMPTE

SYNCHRONIZATION OVERVIEW

This chapter is an overview of the M20’s SMPTE time code features, in addition to the basics covered in Chapter 11. Before you design a synchronization system, and particularly if you have not used time code before, please read this chapter carefully. It is impossible for any manual to cover all the possible combinations of synchronizers, decks, automated mixing consoles, sequencers, and video editors; but a solid understanding of synchronization principles will help you be successful no matter what equipment you plan to combine with the M20.

16.1SYNCHRONIZATION BASICS

When machines are synchronized, they move together at exactly the same speed, passing through corresponding locations. To do this, there must be some kind of time marker recorded continuously on each machine, along with the audio and video tracks. One machine must be designated the master or controlling machine, and others are considered slaves. Each slave machine must have the intelligence to compare the incoming time signal from the master machine to its own location, and speed up, slow down, or locate to match the master’s position. When it’s doing this, this is called chase mode.

MASTER OR SLAVE?

The M20 may be used as master or slave because of its built-in time code synchronizer. When it’s a master, you command the entire recording system by using the transport controls on the M20 (or CADI). The M20’s SMPTE OUT jack will issue SMPTE time code (depending on the parameters you set) to video or other audio decks. If they are also equipped with synchronizers and are in chase mode, they will follow the M20 system’s lead.

When the M20 is used as a slave, it receives time code from the master (a video deck, hard disc recorder, or edit controller) and moves to match it, depending on the M20’s time code and SMPTE Chase parameters. On a slightly higher level, it may also receive direct commands (play, rewind, record etc.) from a controller via MIDI Machine Control or (when 2.0 software becomes available) via the RS-422 port.

DIGITAL TIMING REQUIREMENTS

In addition to SMPTE time code synchronization, digital audio recording has its own synchronization needs. When recording from a digital source (either ADAT Optical or the optional EC-1 AES/EBU card), the M20’s speed must match the flow of digits as they come in. This can lead to certain problems that analog recorders did not face.

For example, suppose you have the M20 in SMPTE Chase mode, following time code and video clock from a VCR. You want to record a sound effect from a CD player digitally into the AES/EBU card at a certain cue. But at the cue, when you press PLAY on the CD player, you notice clicks and pops in the audio. What happened?

ALESIS M20 REFERENCE MANUAL 1.06 16-1