M-Audio Biport 2x4s [38/48] Smpte and mtc user bits

Black and white video frame rates were originally derived from the A/C

line frequency of the indigenous country (e.g. 50 Hz in Europe, 60 Hz in

the U.S.). In the U.S. when color video was introduced, part of the black

and white frame information was used to encode the color information.

The result was that the color frame rate ran at an effectively slower rate

of 29.97 frames per second. This slower rate can be approximated by

running at 30 frames per second and skipping 108 frames per hour in the

numbering scheme. This method of “dropping” 108 frames/hour to

slow the effective frame rate was termed “drop frame.” Hence, the stan-

dard frame rate used when doing U.S. color video is called “30 drop

frame”. When running at a true 30 frames per second, this is known as

“30” or sometimes “30 non-drop”.

As listed in the above table, in the U.S. and other “NTSC” countries,

black and white (30 non-drop) and color (30 drop) video have different

frame rates. While in Europe and all “PAL” countries, black and white

and color video have the same frame rate of 25 frames per second.

What Frame Rate and Settings Should You Use?

The following table summarizes the frame rates that we recommend you

use when striping SMPTE:

Application Frame Rate

Audio Only 30 non-drop

Video - Color U.S. 30 drop*; 29.97

Video - B/W U.S. 30 non-drop

Video - Color Europe 25

Video - B/W Europe 25

Note: If you are in the U.S. and using a BiPort 2x4s to do

audio scoring or MIDI sequencing for your own video, then

we suggest you use 30 non-drop instead of 30 drop. This is

because drop-frame is harder to work with, since time cal-

culations are more complicated. Non-drop will allow you to

sync just as well drop-frame; drop-frame is really only a

necessity for broadcast purposes.

SMPTE and MTC User Bits

The SMPTE and MTC standards provide a means for users to “stamp”

their media with reference numbers of their own choosing. This is

accomplished by setting aside some spare data (32 bits) within the time

code message to be used as “User Bits.” SMPTE and MTC allow you to