Polarman
Joined: 24 Jun 2005
Posts: 55
Location: Barbados |
| Week 9 - Timecode |
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1. Why was timecode invented?
2. How was videotape originally edited?
3. Why is dub editing better than cut and splice?
4. How accurate is dub editing?
5. What did SMPTE develop in 1967?
6. Is frame-accurate editing possible using timecode?
7. What types of equipment may be synchronized with timecode?
8. Comment on the similarity between timecode and an audio signal.
9. What two types of information does timecode contain?
10. How does this compare to the sprocket holes on film and the edge numbers?
11. Explain 10:00:00:00.00 in detail.
12. Describe four kinds of code that could be used to represent timecode
13. Describe in detail the operation of biphase mark code.
14. Why is it important that timecode should not be affected by polarity inversion.
15. Why is it important that it should be possible to read timecode backwards?
16. What frame rates are in use?
17. What is the mains frequency in use in the USA?
18. What was the frame rate of monochrome US television?
19. Why was the frame rate changed to 29.97fps for NTSC colour?
20. What difficulty does this cause for timecode?
21. Compare this to the use of leap years.
22. What is 'drop frame' timecode?
23. Why is the term 'drop frame' misleading?
24. Describe the operation of drop frame timecode.
25. Why is it inconvenient to use 29.97 fps drop frame timecode during the production process?
26. If 29.97 fps non-drop frame timecode is used, what problem do you have to bear in mind?
27. If 30 fps timecode is used, what problem do you have to bear in mind?
28. Is 30 fps drop frame timecode ever used?
29. Where does timecode come from?
30. From what code does timecode generation start?
31. Does timecode ever copy the time of day?
32. Why is it not a good idea to start timecode generation at midnight?
33. Comment on the generation of timecode for analogue audio only purposes?
a. On which track should timecode be recorded?
b. Is a guard track necessary?
c. What is the effect of timecode crosstalk into an adjacent track?
d. What is the effect of low frequency crosstalk into the timecode track?
e. Does LF crosstalk occur on record or playback?
f. Should timecode be routed through a mixing console?
g. At what level should timecode be recorded?
34. What does a timecode reader do when there are dropouts in the timecode?
35. What is 'reshaping'?
36. What is 'regeneration'?
37. What is 'jam sync'?
38. Why is jam sync useful?
39. What is 'house sync'?
40. What is 'genlock'? |
Tue May 02, 2006 5:56 am |
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JakoBee
Newbie
Joined: 19 Apr 2007
Posts: 4
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Week 9 - Timecode
1. Why was timecode invented?
IT was invented to synchronize the film recorded by cameras with audio recorded on tape recorders having a chronological record of the absolute time in recording.
2. How was videotape originally edited?
Originally videotape was edited by physically cutting and splicing the tape.
3. Why is dub editing better than cut and splice?
In dub editing you don’t have to physically cut the tape and splice it back together. And it’s much faster.
4. How accurate is dub editing?
Fairly precise.
5. What did SMPTE develop in 1967?
Electronic Timecode
6. Is frame-accurate editing possible using timecode?
Time code is what makes frame-accurate editing possible.
7. What types of equipment may be synchronized with timecode?
video and audio decks, computer sequencers, hard disks may synchronize with the timecode. A Master (Video Tape) dictates the timecode and the slaves (other video decks, audio decks, seqeuncers etc) are genlocked (line by line synchronized) to that master assuring precise sync.
8. Comment on the similarity between timecode and an audio signal.
They are both aligned along the edge of the videotape.
9. What two types of information does timecode contain?
source identification information (this identifies the source; for example, a given videotape)
timecode format information (this specifies the characteristics of the timecode and how to interpret the timecode information)
frame numbers
All consisting of the binary numbers.
10. How does this compare to the sprocket holes on film and the edge numbers?
Well I guess this could be called the “analogue” timecode. Sprocketholes and edge numbers are no way near as precise as the digital way
11. Explain 10:00:00:00.00 in detail.
Reel number: Hour: Minute: Second: Frame
12. Describe four kinds of code that could be used to represent timecode
VITC, LTC “Drop frame Or NON Drop frame”, MTC
13. Describe in detail the operation of biphase mark code.
Using biphase mark code makes synchronization easier by ensuring that there is at least one transition on the channel between every data bit. BMC coding provides a better synchronization since there is a change in the polarity at least every two bits, which prevent phase interruption.
14. Why is it important that timecode should not be affected by polarity inversion.
To avoid dropouts.
15. Why is it important that it should be possible to read timecode backwards?
To be able to rewind, without losing accuracy.
16. What frame rates are in use?
24(film) 25(PAL or SECAM) 30(NTSC) Black and White, in color 29,97
17. What is the mains frequency in use in the USA?
60 Hz
18. What was the frame rate of monochrome US television?
30
19. Why was the frame rate changed to 29.97fps for NTSC colour?
When color TV was introduced, the color information was added via subcarriers. Those subcarriers takes up.3 fps.
20. What difficulty does this cause for timecode?
To fit in the color information you have to skip 2 frames pr. Second except for every tenth minute – 10, 20, 30, 40, 50, 60, 00 etc.
21. Compare this to the use of leap years.
Like in our calendar system we have to add one day per 4 years
22. What is 'drop frame' timecode?
To fit in the color information you have to skip 2 frames pr. Second except for every tenth minute – 10, 20, 30, 40, 50, 60, 00 etc.
23. Why is the term 'drop frame' misleading?
The “dropped” frames are only skipped, not dropped.
24. Describe the operation of drop frame timecode.
Once again - To fit in the color information you have to skip 2 frames pr. Second except for every tenth minute – 10, 20, 30, 40, 50, 60, 00 etc.
25. Why is it inconvenient to use 29.97 fps drop frame timecode during the production process?
29,97 fps. is actually a little bit faster than the real time.
26. If 29.97 fps non-drop frame timecode is used, what problem do you have to bear in mind?
In 2 hours you will actually be 3.6 min out of sync.
27. If 30 fps timecode is used, what problem do you have to bear in mind?
It has to be converted if you are operating with NTSC.
28. Is 30 fps drop frame timecode ever used?
Yes but at 30 Drop Frame format the clock will stay correct to within a theoretical 75ms in 24 hours.
29. Where does timecode come from?
Usa
30. From what code does timecode generation start?
The timecode start is often set to 01:00:00:00 .. then you have 1 hour of roll back. Let’s say you set the start point to 00:00:00:00 and you roll back the master tape just a little bit as 3 seconds, the slave will roll forward to 23:59:57:00. Set the start point to 01:00:00:00 and your tape won't roll of the reel.
31. Does timecode ever copy the time of day?
The latter mode or the "time of day" mode is when timecode runs continously recording the actual time of day. It’s used when using multiple cameras on the same shoot. you have to synchronize the timecode start points and then the editor can synchronize the recordings easily.
32. Why is it not a good idea to start timecode generation at midnight?
Because the change from lets say 23:59:59:29 to 01:00:00:01 make a new start of the timecode
33. Comment on the generation of timecode for analogue audio only purposes?
a. On which track should timecode be recorded?
The highest track, next to one track not in use.
b. Is a guard track necessary?
Yes, this eliminates crosstalk interference and guard bands so that more tracks of data can be stored on a tape.
c. What is the effect of timecode crosstalk into an adjacent track?
Well too loud it’s hearable through the audiostream, too low it’s unreadable.
d. What is the effect of low frequency crosstalk into the timecode track?
This usually happens when low frequent sounds (musical instruments) are recorded next to the timecode track. It’s very important to avoid, cause it can screw up the sync. Which by the way, is why they make guard tracks.
e. Does LF crosstalk occur on record or playback?
It can happen yes, depends on how bad it is.
f. Should timecode be routed through a mixing console?
Well that definitely depends on the console. If it’s a noisy one, it can cause crosstalk in the same way as a bassguitar. So unless you have a very good reason too, avoid it at all cost.
g. At what level should timecode be recorded?
For digital tape -7db and for analog tape -3db
34. What does a timecode reader do when there are dropouts in the timecode?
Freewheeling (Flywheel). The reader acts like nothing happened and awaits the sync. To yet again fall into place.
35. What is 'reshaping'?
Regeneration of lost or worn out time code tracks.
Basically the process of filtering the incoming timecode signal and restoring its electrical properties. In detalis: when timecode comes off a tape machine it sometimes doesn't have a constant signal, which can be hard to read. Reshaping is detecting the signal at a low threshold and then reshaping it to the proper level.
36. What is 'regeneration'?
A master tape can only be copied 2 times over, before the timecode wears out, so basically regeneration is a fresh copy off the master.
37. What is 'jam sync'?
Regenerated timecode
38. Why is jam sync useful?
When you record or shoot with multiple systems at the same time.
39. What is 'house sync'?
When sync. is done line by line, instead of frame by frame.
40. What is 'genlock'?
When sync. is done line by line instead of frame by frame.
When multiple device’s are getting timecode off of the same machine. |
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Mon May 14, 2007 7:44 am |
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