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24—MIDI and Synchronization
Roland VS-2480 Owner’s Manual www.rolandus.com 309
numbers per second. It can either show 29 per second or 30, but there’s no way to
display only a fraction of a counter number—a number’s either shown or it isn’t.
A technique called the “drop frame” was devised by the video industry to deal with
this. With a frame rate called “29.97 drop,” the first two frames in every minute are
discarded except for the first minute and every tenth minute. This keeps the time code
and a counter roughly together. In fact, they’re always a little bit off from each other,
but each time the frames are dropped, the time code leaps ahead to catch up to the
counter temporarily. This form of time code isn’t completely continuous—since it has to
keep skipping over frames to catch up—but it’s useful in situations where the counter,
and the clock on the wall, has to match the time code as closely as possible. It’s
therefore the most commonly used time code in the live broadcasting of color video.
29.97 non-drop time code is its continuous cousin. It doesn’t drop any frames and is the
preferred frame rate when the counter’s accuracy doesn’t matter so much. Continuous
time code is theoretically smoother than time code that jumps around skipping frames.
Which Frame Rate Should You Use
If you’re syncing and there’s no video or film involved, use the 30 fps frame rate unless
one of your devices doesn’t support it. This frame rate’s continuous and has the finest
possible resolution, being the fastest speed available. If you’re syncing the VS-2480 to
an external device that has to use another frame rate—for example, a video editing
system—simply set the VS-2480 to the frame rate the external device uses. We’ll
describe setting the VS-2480’s FRAME RATE parameter in the following sections.
MMC
MMC, short for “MIDI Machine Control,” is a set of MIDI messages that controls the
transport buttons—PLAY, STOP, etc.—of an MMC-supporting device. MMC also
contains information that tells each device the current location of its transport. In the
VS-2480, this would be the position of its timeline. MMC’s not a form of sync—it’s
about button-presses: When you press the PLAY button on a master MMC device, an
MMC slave device acts as if its PLAY has been pressed as well. The VS-2480 can act as
an MMC master or slave.
Synchronization with Tempo Changes
Its’ not uncommon for a piece of music to use more than a single tempo or time
signature. Since MTC/SMPTE speeds are unaffected by tempo or time signature, MTC/
SMPTE time code doesn’t contain tempo or time signature information. If you want a
sequencer you’re syncing to the VS-2480 to speed up or slow down—or change time
signatures—in order to follow what’s recorded in a project, you can synchronize the
two devices using MIDI clock and Song Position Pointers (Page 308).
The VS-2480 can transmit this form of synchronization as a:
•
sync track
—a single, uneditable stream of MIDI clock/SPP synchronization data.
The VS-2480 can record a sync track comprised of captured MIDI clock and Song
Position Pointer data received from an external MIDI device. This lets an external
sequencer “teach” the VS-2480 a song’s tempo and time signature changes. The
In order for MMC to work, the master device’s SysEx transmission must be enabled—
in the VS-2480, this is the SysEx. Tx Sw parameter on the MIDI PARAMETER screen
(Page 299). The slave device’s SysEx reception must also be turned on. For the VS-2480,
this is the SysEx. Rx Sw parameter, also on the MIDI PARAMETER screen.
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