Can a digital camera tc drift WHILE rolling?

[Shastapete]

Martin,

A device cannot drift on its own unless it is being compared to another device keeping time. Every piece of timecode equipment has a level of precision:

Sound Devices 688: ± 0.2 ppm (0.5 frames per 24 hours)
Zaxcom Nomad: 1.54 PPM (1 frame out in 6 hours) 
Denecke TS-C: Typical ±0.2 ppm @ 23° C ±1 ppm @ -30° to +75° C
Betso SBOX-1N: Temperature compensated oscillator (+/- 0.2 ppm) Less than 0.5 frames / 24 hours

If you run them for 24 hours they'll all have slightly different values at the end of the day.

Which one has the correct value? All of them? None of them? Did the 688 drift or did the Betso?

[Abe Dolinger]

Maybe this is the simplest explanation: what changes is the measurement of the second you're recording. Not the number of frames, not the length of the take. A second doesn't occur in nature - it's a human construct.

The NIST uses an atomic clock - measuring the decay of isotopes - as the US standard for how long a second is. We don't have that luxury in our equipment, and so everyone arrives at very, very similar, but always slightly different results. 

So, some gear will say that it's recorded 25 frames in one second, but another piece will say those 25 frames lasted 1.000002 seconds. And that's just in the case of very good gear. With budget clocks, it might be 1.001 seconds, or worse.

Hope I didn't add to the confusion. 

Edited June 29, 2016 by Abe Dolinger
Wording

[Bash]

12 hours ago, Nathaniel Robinson said:

Everyone keep your hats on for one more moment! Within Simon B's excellent and thorough explanation is one simple mathematical error. 90 frames out of 90,000 would be 0.1% drift (or a multiplication factor of 0.001, which is likely the mix up).

Apologies - it was very late at night, and I had had a long day!!!!

 

2 hours ago, MartinTheMixer said:

Al, I don't think that you were here for the part. If that were the case then two devices don't match are they each doing their "own thing". If a clock is not keeping the correct time I would call that drifting. 

I think the word fopr this is 'plesiochronous', where a number of different things, or devices, which nominally run at the same speed, in reality run a ever so slightly different speeds. It is inevitable particularly with portable equipment.....

 

sb

[chrismedr]

I've just read through all this and I'm a bit confused what the confusion is about : )

In a perfect world, all cameras and sound recorders would have atomic clocks in them that would resync over radio all the time (if you don't do that, even atomic clocks may run out of sync due to the law or relativity, see the GPS satellites - actually that might be not quite right, I've read that they have the correction factors are already built in due to some people being really good at math so they know how much they will drift!).

anyway, since we don't live in a perfect world and cost is an issue (tm), each clock will drift apart from the perfect mathematical time sooner or later (check your wrist watch).

thus, every device that uses it's own clock will generate numbers as well as they can, but of course they aren't the same, and so if you want to be sure that two devices have the same numbers you need to either make sure that both have very accurate clocks or you'll need to feed them a master clock and make sure they are able to listen to it.

or in short, the reason RED cameras drift is that they don't have accurate enough clocks inside to suit our purpose to keep in sync with other devices.

chris

ps: this made me just realise, would be nice if manufacturers would use GPS signals to sync their internal clock. a quick search seems to indicate that those are easily readable to 40ns (i.e. about 1/1'000'000 of a frame). no more sync boxes, no more sync cables, just roll and be in sync  : )

 

[Constantin]

ps: this made me just realise, would be nice if manufacturers would use GPS signals to sync their internal clock. a quick search seems to indicate that those are easily readable to 40ns (i.e. about 1/1000 of a frame). no more sync boxes, no more sync cables, just roll and be in sync  : )

 

Yes they are precise, but only if you have satellite link, which I often find I don't have. Like almost always when I'm inside

[chrismedr]

6 minutes ago, Constantin said:

Yes they are precise, but only if you have satellite link, which I often find I don't have. Like almost always when I'm inside

yeah, good point.

time data should be accurate with only one satellite signal though (whereas for accurate position you'd need 4 or so). still, probably a lot of places that would be problematic... hmm., time to look around for GPS repeaters : )

[Constantin]

yeah, good point.

time data should be accurate with only one satellite signal though (whereas for accurate position you'd need 4 or so). still, probably a lot of places that would be problematic... hmm., time to look around for GPS repeaters : )

No, please don't. That would totally negate you point of having this integrated into your recorder and still will not help the OP.

The timecode devices we have today are plenty accurate enough. His issues seem to be of a different nature

[Freeheel]

Thanks Chris... You HAD to drag in Einstein and the theory of relativity...  Now Martin is going to have to worry about how fast the camera is moving in relation to the sound recorder, as well...

:-)

Cheers,

Brent Calkin

[chrismedr]

3 hours ago, Constantin said:

No, please don't. That would totally negate you point of having this integrated into your recorder and still will not help the OP.

that was actually a joke : )

i did bring up the hole thing because of the discussion about "which clock is accurate" and i would argue that the one in the GPS timings or the one for RCC (radio controlled clocks) would probably be a good candidate. RCC signals would probably be the better clock to synch time code generators to since they likely work in most locations, and even though you don't know how far away the signal is broadcast the delay would hardly ever be more then 1/4 frame.

btw, I should mention that I fully assume companies like ambient looked into those options when they started their own wireless time code system and decided that it's not a good idea (or maybe a good idea but difficult to implement) 

1 hour ago, Freeheel said:

Thanks Chris... You HAD to drag in Einstein and the theory of relativity...  Now Martin is going to have to worry about how fast the camera is moving in relation to the sound recorder, as well...

hehe - and just imagine what happens if the camera operator calls "speed".

chris

 

 

[Constantin]

Ambient do have the ACC501, to which a GPS module can be connected

[Ze Frias]

15 hours ago, MartinTheMixer said:

Jose, I am ok with everything you just said, except the "drift" part. I call a device that can't maintain its own time code, drifting. What do you call that?

There's a flaw in the way you choose to phrase things, and perhaps that adds to the confusion.

Every device that generates timecode can maintain its own timecode. It doesn't need an external device to continue to generate timecode values for each new file. However, when compared to another device generating the same timecode values, what you may notice is that there's a difference between the speed at which each different device generates each timecode value. This difference may become especially noticeable after a long period of time. THAT is drift.

[al mcguire]

Thank you, Jose

[John Blankenship]

What is the sound of one clock drifting?

 

[Christian Spaeth]

I think Martin has all the important info by now in this thread. The only addition I can think of: while every device is pretty much always in sync with itself (its timecode values, if stamped, are in sync with its internal clock), no two clocks will ever run 100% in sync, not even two atomic clocks (correct me if I'm wrong). Hence the need for "syncing" cameras and audio recorders, the aim of which is to keep the drift at an acceptable (i.e. unnoticable to the human eye and ear) amount for our purposes.

[al mcguire]

So the question remains, is Martin in sync with the group, or is he drifting ?

[Constantin]

not even two atomic clocks (correct me if I'm wrong).

Actually, once synced they will drift by one second each per 20 million years. I'd say it's safe to say they don't drift. They might be a bit big to be integrated into a recorder.

RCC's however, which receive the signal of an atomic clock (when in range) are small enough to be put into a recorder or camera and that really is an interesting idea

[MartinTheMixer]

15 hours ago, Constantin said:

But how would you know it's drifting?

If you compare to another clock, how would you know it's not the other one drifting? If you only have one clock, would the drift ju

Edited June 29, 2016 by MartinTheMixer
Site broken

[MartinTheMixer]

Ok, the site won't let me respond to a comment, it just says "loading" for a very long time.

How can you a device drift against itself? Several have asked that question. I think some are stuck that a device can't drift without comparison to another device. That's not correct. Let's make this dates, instead of time. If you had a camera, and you set the date, as being 1 June, 2 hours later, you check the camera and it now reads 2 June. 3 hours later, you again check the camera and it now reads 3 June. Unless you consider your brain a device, that camera is drifting the date without being compared to another device. 

Now, if you go back to time, and you set that camera to midnight and 50 minutes later, that camera now reads 1 am, that camera has drifted. 

Part of this discussion was after I brought up a Red Dragon that was "drifting" MANY frames in well under an hour. But I was curious if stamping that first frame with a Tc stamp, might partially cure this. 

I think some learned from this discussion, the conversation about the Arri cameras was interesting.

[Abe Dolinger]

2 hours ago, MartinTheMixer said:

If you had a camera, and you set the date, as being 1 June, 2 hours later, you check the camera and it now reads 2 June. 3 hours later, you again check the camera and it now reads 3 June. Unless you consider your brain a device, that camera is drifting the date without being compared to another device. 

That's the thing - your brain is a device.  Without our brains, there would be no 2 June or 4pm.  The Earth would still be rotating around the Sun, and rotating on its axis, but the camera's not measuring those things.  Humans have come up with the time and date system.  The camera is just taking the best guess it can at consistently dividing its operations into Human Time.

A device can "drift" from itself, as I understand you to mean, if there are errors in its clock, causing it to miss time or change time randomly.  But the RED camera you saw was a few frames out, after an hour.  That means its clock was oscillating around .0001% faster or slower than whatever gear you were comparing it to (probably a nice temperature-controlled oscillator).  It wasn't drifting on its own - it just used a slightly different scheme than your gear to deduce how long a second is.  How did you know the RED was drifting?

[MartinTheMixer]

1 minute ago, Abe Dolinger said:

That's the thing - your brain is a device.  Without our brains, there would be no 2 June or 4pm.  The Earth would still be rotating around the Sun, and rotating on its axis, but the camera's not measuring those things.  Humans have come up with the time and date system.  The camera is just taking the best guess it can at consistently dividing its operations into Human Time.

A device can "drift" from itself, as I understand you to mean, if there are errors in its clock, causing it to miss time or change time randomly.  But the RED camera you saw was a few frames out, after an hour.  That means its clock was oscillating around .0001% faster or slower than whatever gear you were comparing it to (probably a nice temperature-controlled oscillator).  It wasn't drifting on its own - it just used a slightly different scheme than your gear to deduce how long a second is.  How did you know the RED was drifting?

In answer to your question how did I know it was drifting. It was many, many frames out compared to slate and mixer. The camera was fried. I was curious if rolling could "fix" this. In other words, could the frames tell it more accurately what the time should read. Looks like the answer is no.

 

[Abe Dolinger]

Right, compared to the slate and mixer, which were probably jammed together and both had good clocks?  In that case, you could say that those two agreed pretty well on the length of a second, and the Red was taking a different approach.  

The Red (if I recall) jams from external TC at the beginning of a take.  Did you have a sync box on it?  If you did, rolling should have brought the clocks closer together.  If there's no sync box, the camera would content itself with its own time, which would be more obviously different from your clocks the longer you observed the two together.  I have to note that you wouldn't have said the camera was "drifting" unless you had your own gear to compare it to.

[chrismedr]

3 hours ago, Abe Dolinger said:

That's the thing - your brain is a device.  Without our brains, there would be no 2 June or 4pm.  The Earth would still be rotating around the Sun, and rotating on its axis, but the camera's not measuring those things.  Humans have come up with the time and date system.  The camera is just taking the best guess it can at consistently dividing its operations into Human Time.

at the danger of getting philosophical here, I tend to disagree.

Obviously we can go to the point that if there is no observer, then nothing exists. 
but if we leave those arguments out, I strongly argue that there *is* such a thing as time, even without humans. It would not be called "1 hour" or "1 sample of 1/48000 second", these are just human definitions, but as far as science knows, there *is* an time flow which is very definitive. you'll have to take speed and gravity into account, but if you do that it's frighteningly accurate - actually it's the most accurate thing we can measure so far, far more accurate then mass or distance (distance ironically is measured by time and the speed of light because that's *much* more accurate then using a physical device).

so in this point (and only this! ; ), i tend to agree with martin. there is an definite time and we can say a recorder drifts against this value, even without a second device. and I do agree that in a perfect world we would not have to deal with two devices running out of sync because all recorders/cameras would run at this exact time, thus always being in sync (or as constatin mentions, one second off in a few million years).

apparently so far this has been too expensive/difficult to implement, and the tools we have at the moment are not too bad either.

but don't you all agree that it would be nice if all cameras and recorders would sync to a RCC and always be in sync without even thinking about it, every morning, after every battery change?

[Constantin]

Yes that would be nice, although we would still need to have a backup option, in case there is no radio reception.

Ok, so a timecode source, camera or recorder, can drift when compared against "absolute time". Within the confines of "our" world, though, it can't or at least it won't matter.

The recording itself will never be affected drifting tc. So to get back to the OP, I still don't get what the actual issue is. Or was this more of a philosophical question from the get-go?

[MartinTheMixer]

3 hours ago, Abe Dolinger said:

Right, compared to the slate and mixer, which were probably jammed together and both had good clocks?  In that case, you could say that those two agreed pretty well on the length of a second, and the Red was taking a different approach.  

The Red (if I recall) jams from external TC at the beginning of a take.  Did you have a sync box on it?  If you did, rolling should have brought the clocks closer together.  If there's no sync box, the camera would content itself with its own time, which would be more obviously different from your clocks the longer you observed the two together.  I have to note that you wouldn't have said the camera was "drifting" unless you had your own gear to compare it to.

Hello, it was receiving sync from zaxnet. I am sure, that the camera was receiving timecode. It was out MANY frames in an hour. I was just curious if rolling could fix this,some, since the camera would know how many frames it had shot and compute from there.

[Abe Dolinger]

4 hours ago, chrismedr said:

I strongly argue that there *is* such a thing as time, even without humans. It would not be called "1 hour" or "1 sample of 1/48000 second", these are just human definitions, but as far as science knows, there *is* an time flow which is very definitive. 

so in this point (and only this! ; ), i tend to agree with martin. there is an definite time and we can say a recorder drifts against this value...

Yes, you're correct, and sorry if I phrased it to the contrary. My point is that the idea of dividing time into seconds is a (recent-ish) human thing, not that time itself is a human idea. 

Also, for those curious: the original atomic reaction was clocked using "ephemeris time", in this case measuring the movement of the moon, against the decay of a cesium isotope. And even then, there was some variation in the results, so we use an average as our standard. Time's tough to measure.