Roland VS-2400CD Owner's Manual page 294

23—MIDI and Synchronization
What Do We Mean By "Timing Reference?"
A timing reference is a kind of message continuously transmitted from master to slave
to keep the devices synchronized. The VS-2400CD works with two types of timing
references when synchronizing its hard disk recorder with another device.
SMPTE/MTC
The film and video industries use a steady stream of timing data called "SMPTE time
code" to keep devices tightly synchronized with each other as they play. A form of
SMPTE called "MIDI Time Code," or "MTC" can be transmitted and received through
MIDI cables along with other MIDI data. Both SMPTE and MTC provide very accurate
synchronization. The time code area of the VS-2400CD's current time location display
(Page 122) shows MTC/SMPTE hours, minutes, seconds frames and subframes.
The VS-2400CD can be synchronized to any device that generates either SMPTE or
MTC. Since most VS-2400CDs are used with MIDI devices, MTC is used more
frequently than SMPTE. Most sequencers support MTC, for example—not as many
support SMPTE. The VS-2400CD itself generates MTC.
MIDI Beat Clock
MIDI beat clock—or "MIDI Clock" for short—is a pulse embedded in a stream of MIDI
data that can be used for synchronizing MIDI devices. MIDI clock synchronization isn't
as accurate as MTC-based synchronization. It does have one important use, however.
MIDI clock, along with MIDI Song Position Pointer ("SPP") messages, passes along
tempo and time signature information that can be used by the VS-2400CD in the
creation of sync tracks and tempo maps, which we'll discuss in a moment.
The VS-2400CD can record received MIDI clock information as a sync track that lets it
act as a master to slave devices that understand MIDI clocks and Song Position Pointer.
While the VS-2400CD can generate MIDI clocks to slave devices that use this form of
sync, the VS-2400CD itself can't be synchronized to MIDI clocks, since it's not an
accurate enough form of synchronization for the VS-2400CD's precise operations.
Song Position Pointer
About MTC/SMPTE Frame Rates
When you use MTC or SMPTE for synchronizing the VS-2400CD with an external
device, you'll need to make sure that the two devices are set to operate at the same
MTC/SMPTE speed, called the "frame rate." The "frame" refers to how many frames of
film or video occur in each second.
MTC and SMPTE can run at a few different frame rates, depending on the devices
being synchronized and the materials they're producing. It can run at:
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30 fps ('frames per second")—This speed is used by most MIDI sequencers and audio
devices. Black and white video also runs at this speed.
29.97N ("non-drop") fps—This is the speed at which United States' NTSC format
color video runs in non-time-critical situations, such as offline production work.
29.97D ("drop") fps—This is the speed at which United States' NTSC format live
color video runs during broadcasts and other time-critical situations.
25 fps—This is the speed at which European SECAM or PAL film, video and audio
equipment operates.
24 fps—Film, cell animation and certain audio devices run at this speed.
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