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RecorderMan's Primer on TC

Forgive any typos and kill me for anything wrong. .this is off the top of my head.

Here's what I know about TC (Time Code)

Time code was developed in the late sixties by the Society of Motion Picture and Television Enigineers. SMPTE.

there are really only four kinds of TC (not counting Drop and Non-Drop, which are really variations of two of the four kinds mentioned below. later with that):
30 FPS (Frames Per Second)
29.97 FPS
25 FPS
24 FPS

before we talk about the differrences of the above frame rates, know this. Timecode is just that, a code that relates to time that is laid down on a track of tape. It contains hours:minutes:seconds:frames. Lynx is the name of a very popular synchronizer (they were the digidesing of synchronizers, back in the day...) that would be hooked up to a tape machine.
(I'm going to speak of "tape" here...but you can extrapolate this to anything...DAW, etc. And while we mention DAW's. they usually have a way to deal with TC without having to dedicate a track) Whenyou wanted to lock-up two or more tape machines with lynx's you'd have to:
1. Hook up the Lynx's; one to each amchine. There was a special machine cable between the Lynx's and there respective tape machine. This allowed the Lynx's to control the motors and tarnsport control of there respective machine.
2. Hook up all the Lynx's together with a special rs422 cable. This allowed the Lynx's to speak with one another.
3. Hook up the TC generate out of each Lynx to the record input of the designated TC track (usually but not always track #24).
4. Send the return of the track with TC to the reader input of the Hook up the TC generate out of each Lynx for the respective machine.
5. Make one of the Lynx the "master" by selecting it on it's front panel.

after "stripping" (the act of recording time code) all of the reels with the smae timecode. That is, input 1:00:00:00. (i..e One Hour:zero minutes:zero seconds:zero frames) into the generator side of the Lynx. hit record on the tape machine and print for the entire reel lenght or the lenght of the song. It is/was necessary to have code for approximately 20 seconds before nad after the area needed for audio ( I always would print 30 seconds myself) allow time for the Lynx's to Lock up. This typically was around 6 seconds for a well set-up machine/Lynx/etc.

Now so far we've spoken of TC to and from the machine, a machine cable and rs422 between the Lynxes.

Remeber; Time Code tells "us" where we are, per say; it relates to position. the coordinates of our linear map.The "clock" tells TC at what rate to record &/or play back at. How accurate the clock is directly affects the ability of what ever is reading the clock, to do it's job.Timecode referenced to a poor clock is not accurate. If the clock has variations (wow=slow variations, flutter=faster variations, jitter=very fast variations), then the first minute of the hour might be a little under a "real" minute, and the last minute of the hour might be a little longer than a real minute (a very simplistic description...are you following me so far?)

So a tape machine with no synchronization uses the "clock" derived from either the frequency of the AC current (60hz in the US, 50Hz most everywhere else)[called a hystresous motor...where's spell check when you need it); or a built in crystal clock...either way, it's some-what accurate enough for a self contained, all in one, system; but far from usefull if you want to lock two of these puppy's up,

That's why SMPTE (TC) was invented.

So, we have our reels striped.
One's the master..the other's are slaves. When you hit play on the master machine, it's Lynx sends a "hit Play" command through the rs422 cable to the other Lynx's. All michines start to play, the Lynx's of each machine start to read the "code" (another abreviation for SMPTE, or TC) that they are getting. the Lynx's start to "resolve"(adjusting each slave to the master, untill there all sync'd up).

Now in music-only land. this is usually good enough. The lock is still quite loose, in the respect that you would not want to do something like put the left OH track on one machine and the right OH track on a slave machine. You would hear phasing between the two tracks. After all a frame at 30 frames per second is still 33.3ms. Lynx's allow you to work in sub-frames which gets you down to 0.3ms per sub-frame; but analog machines still have lots of machanical parts that make it damn near impossible to reliably lock tighter than this. Yet this is just fine for music only. Just keep all the tracks related to a single musical entity (like all the drum mics for one drum kit) on the same tape machine.

Television, Film, etc. Anything in which a visual cue must be locked with audio, needs something a lot more accurate-our "eyes" are more accurate than our "ears"-to make this work even better(i.e. tighter).

Up until now, our example Lynx's had derived ther clock from an internal crystal. But we haven't (in our example) sent clock anywhere.

In TV we use what's know as "black"."Black" (or "Video Ref" or "NTSC composite sync" as it's also called) is a clock derived from the space between the two fields, that make up each frame of video. It's only one of several "clock's" that can be sent and recieved by various sync devices (like the Lynx's, or a Universal Slave Driver (USD), for you Pro Tools people). We can also use "Pilot tone" (this is the name for the 50/60hz volatge from the power current, and or "Bi-phase/Tach", this is what the tape machine uses itself internally if left to it's own devices. The last two "Pilot" and "Tach" are rarely if ever used.
[as a side note: "Sargent Pepper's..." was recorded on 4 track, and they used a homemade version of sync by pilot tone to lock up two 4-tracks to record the occhestra on A Day in the Life. One 4-track had the band pre-records and the other recorded the orchestra...very cutting edge in it's day!]

So...we send "black" from a "black" generator to the "video reference sync input" of all Lynx's, VTR's etc in the room. NOW, everybody has the same "CLOCK" (i.e video "black") and can now lock up very tightly to their corresponding code.

OK! I've got to go to work click on the link below. It'll sen you to a PDF of the manual for the FRAMEMASTER II, timecode calculator @calculated industries. I only need it a couple of times a year now (what with Pro Tools)...but when it was all analog this little gizmo made me look like a genius more than once (Fixed a slave that George Harrison has sent back with TC wiped half way through...actually i didn't use the frame master for that...that WAS my own genius that time)

anyway...they explain TC VERY well in this manual for the frmemaster (this is not an guys with DAWS don't need's just a great explanation on TC. and I can't won;t copy it here because of copyright, etc.)

Once you get there, the material to read begins on page#4

By the's another great SMPTE resource...none other than the horses mouth (so to speak)

they have a message board, store to by books and test tapes, etc, and links to other august engineering societies, etc. very cool!

CHEERS...recorderman :tu:


Henchman Fri, 09/06/2002 - 15:35

The reason north america ended up with 30fps and Europe with 25 fps, is because of the AC. They needed a single clock source to make sure that picture was played at the right speed, no matter where in the country you were. The only concistent thing everywhere was, of course, AC. Europe has 50 hz, wich they divided in2 and made it a 25fps pulse. And of course North America ended up with 60hz dived by 2. 30fps.



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