[time-nuts] time-nuts Digest, Vol 114, Issue 7
BD Systems Inc.
bdsysco at yahoo.com
Fri Jan 3 10:56:06 EST 2014
Re: Measuring TV Delays
With regard to:
"On 02/01/14 20:33, Bill Hawkins wrote:
> IIRC, the reason why NTSC has an almost 30 fps rate is that early
> vacuum tube TV sets could develop heater-cathode leakage that
> would put a black "hum bar" in the picture. Almost 30 allows the
> bar to move through the picture in a 60 Hz power distribution
> system. Seems like Europe would have had that problem."
Not Quite.
Before Color transmission was introduced, The field rate and frame rate was exactly 60 fields/sec and 30 frames/sec, respectively. The Frame rate was shifted as a result of the change in the horizontal line rate, primarily to avoid interference with the FM sound carrier when color transmission was adopted .
"In January 1950, the Committee was reconstituted to standardize color television. In December 1953, it unanimously approved what is now called the NTSC color television standard (later defined as RS-170a). The "compatible color" standard retained full backward compatibility with existing black-and-white television sets. Color information was added to the black-and-white image by adding a color subcarrier of 4.5 × 455/572 = 315/88 MHz (approximately 3.58 MHz) to the video signal. To reduce the visibility of interference between the chrominance signal and FM sound carrier required a slight reduction of the frame rate from 30 frames per second to 30/1.001 (approximately 29.97) frames per second, and changing the line frequency from 15,750 Hz to 15,750/1.001 Hz (approximately 15,734.26 Hz)." See Wikipedia http://en.wikipedia.org/wiki/NTSC#Lines_and_refresh_rate.
BD Systems
On Friday, January 3, 2014 5:29 AM, "time-nuts-request at febo.com" <time-nuts-request at febo.com> wrote:
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Today's Topics:
1. Re: Measuring TV delays (Gregory Muir)
2. Re: Measuring TV delays (Frederick Bray)
3. Update on my previous note regarding NBS television timing
reference experiment (Gregory Muir)
4. Re: Update on my previous note regarding NBS television
timing reference experiment (Chuck Harris)
5. Re: Update on my previous note regarding NBS television
timing reference experiment (Robert Atkinson)
6. Re: Measuring TV delays (David J Taylor)
7. Re: Measuring TV delays (Magnus Danielson)
----------------------------------------------------------------------
Message: 1
Date: Thu, 2 Jan 2014 15:45:07 -0700
From: "Gregory Muir" <engineering at mt.net>
To: <time-nuts at febo.com>
Subject: Re: [time-nuts] Measuring TV delays
Message-ID: <0B9DF1E83D4E4B81AC3555E776EF9B6F at D32K5JC1>
Content-Type: text/plain; charset="iso-8859-1"
Not certain as to how NBS achieved the transfer of timing accuracy but it was not believed to be in the VITS interval. If I can recall, there was a special waiver (FCC/NTIA) that was required in order to run the experiment. And it required some esoteric hardware to decode the signal at the other end. Mind you, this project was for local timing information dissemination only and didn't relate to programming aspects. This project was above and beyond the use of the local transmitted television signal sync pulses that NBS was using to synchronize the Fort Collins atomic clocks with the Boulder ones.
I do agree, for those of us who tend to dabble in the sub-yoctosecond world, :) something like this is would be a rather coarse approach.
Greg
On Thu, 02 Jan 2014 19:15:13 +0100, Magnus Danielson wrote:
>Just to help confusing matters even more, SMPTE-12M time code (which is
>what you can suspect to be in the TV-signal) and it's Drop-frame
>algorithm causes a drift of time over the day, as the drop-frame
>mechanism isn't perfectly aligning up to 30000/1001 frames per second
>over the 86400s day. This requires the production-time to be jammed into
>alignment regularly, such as every day (off-hour). With the evolving
>standards, the halting mechanics of drop-frame correction is not
>changed, but just standardized. The jamming mechanism is also used for
>leap-seconds and DST change-overs.
>So, in the US and other 30000/1001 frames per second countries (formerly
>NTSC), encoded time is not going to be useful for precision work. For us
>in the 25 frames per second world, we only need to jam for leap-seconds
>and DST change-overs, but that is enough of an upset, but can be more
>easily predicted with only a few handful of bits extra information.
>I prefer using MLS measurement for audio delay measurement. If you do it
>right, you get 20,833 us step resolution, as a result of the 48 kHz
>sampliung clock. MLS delay measurement is trivial using the Analog
>Precision test-set.
>Cheers,
>Magnus
------------------------------
------------------------------
Message: 2
Date: Thu, 2 Jan 2014 15:05:23 -0800
From: Frederick Bray <fwbray at mminternet.com>
To: Discussion of precise time and frequency measurement
<time-nuts at febo.com>
Cc: "time-nuts at febo.com" <time-nuts at febo.com>
Subject: Re: [time-nuts] Measuring TV delays
Message-ID: <AF3D4D1B-D046-4E5A-A1FB-D6EA43655218 at mminternet.com>
Content-Type: text/plain; charset=us-ascii
We have noticed the same problem on some channels with Charter here in southern Calif. As noted, there can be a problem with recordings as a result.
F. W. Bray
Sent from my CP/M phone!
On Jan 2, 2014, at 9:48, Joe Leikhim <jleikhim at leikhim.com> wrote:
> Here in Orlando, Brighthouse seems to have a delay of some 10's of seconds for program material while the cable box through some magic of the internet seems to be on time. As a result, the last seconds of some recorded programs are lost.
------------------------------
Message: 3
Date: Thu, 2 Jan 2014 16:31:02 -0700
From: "Gregory Muir" <engineering at mt.net>
To: <time-nuts at febo.com>
Subject: [time-nuts] Update on my previous note regarding NBS
television timing reference experiment
Message-ID: <13B252DFE48B4CCEB57547F602DEE962 at D32K5JC1>
Content-Type: text/plain; charset="iso-8859-1"
I did a little digging and managed to find a paper on the original television time experiment which was authored by David Howe of NBS, now head of the Time and Frequency Metrology Group at NIST. It can be found at http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=2&cad=rja&ved=0CDYQFjAB&url=http%3A%2F%2Fwww.researchgate.net%2Fpublication%2F3092613_Nationwide_Precise_Time_and_Frequency_Distribution_Utilizing_an_Active_Code_within_Network_Television_Broadcasts%2Ffile%2F9fcfd5089a1d534c56.pdf&ei=Ze_FUsrXJ-LsyQGY0oHYCw&usg=AFQjCNGw2wK-8_RYN98R_72AlRLcm2BAUA&bvm=bv.58187178,d.aWc(Google cached - whew!).
I stand corrected in my assumption that the timing signal was not related to the VITS interval in the video signal. They actually were inserting the signal on line 1. At the time Mr. Howe was involved in the development of the hardware that was deployed in the field for the experiment. He stated that the received code provided unambiguous time to 12 hours, with a resolution of 1 nanosecond and long-term stability of 10 nanoseconds for 10-second averaging.
It's rather odd as to why I can't remember the sordid details off the top of my head regarding a project that took place 42 years ago....
Greg
------------------------------
Message: 4
Date: Thu, 02 Jan 2014 20:58:08 -0500
From: Chuck Harris <cfharris at erols.com>
To: Discussion of precise time and frequency measurement
<time-nuts at febo.com>
Subject: Re: [time-nuts] Update on my previous note regarding NBS
television timing reference experiment
Message-ID: <52C61930.9080707 at erols.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
I had one of the remote units for this system many years ago. I scrapped
the unit and used the cute little 5" Sony Trinitron TV for many years...
I think I still have all of the PCB's that did the line extraction, and
phase locking...
-Chuck Harris
Gregory Muir wrote:
> I did a little digging and managed to find a paper on the original television time
> experiment which was authored by David Howe of NBS, now head of the Time and
> Frequency Metrology Group at NIST. It can be found at
> http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=2&cad=rja&ved=0CDYQFjAB&url=http%3A%2F%2Fwww.researchgate.net%2Fpublication%2F3092613_Nationwide_Precise_Time_and_Frequency_Distribution_Utilizing_an_Active_Code_within_Network_Television_Broadcasts%2Ffile%2F9fcfd5089a1d534c56.pdf&ei=Ze_FUsrXJ-LsyQGY0oHYCw&usg=AFQjCNGw2wK-8_RYN98R_72AlRLcm2BAUA&bvm=bv.58187178,d.aWc
> (Google cached - whew!).
>
> I stand corrected in my assumption that the timing signal was not related to the
> VITS interval in the video signal. They actually were inserting the signal on
> line 1. At the time Mr. Howe was involved in the development of the hardware that
> was deployed in the field for the experiment. He stated that the received code
> provided unambiguous time to 12 hours, with a resolution of 1 nanosecond and
> long-term stability of 10 nanoseconds for 10-second averaging.
>
> It's rather odd as to why I can't remember the sordid details off the top of my
> head regarding a project that took place 42 years ago....
>
> Greg _______________________________________________ time-nuts mailing list --
> time-nuts at febo.com To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nutsand follow the
> instructions there.
>
------------------------------
Message: 5
Date: Fri, 3 Jan 2014 07:23:06 +0000 (GMT)
From: Robert Atkinson <robert8rpi at yahoo.co.uk>
To: Discussion of precise time and frequency measurement
<time-nuts at febo.com>
Subject: Re: [time-nuts] Update on my previous note regarding NBS
television timing reference experiment
Message-ID:
<1388733786.68520.YahooMailNeo at web133202.mail.ir2.yahoo.com>
Content-Type: text/plain; charset=iso-8859-1
Here in the UK we had a version of this for nearly 40 years. It was called Ceefax or TeleText. Chunky graphics with the time, weather and lots of other information. it was also used for closed captioning. see < http://en.wikipedia.org/wiki/Teletext?> It was the best generally available time source for years.
?
Robert G8RPI.
________________________________
From: Gregory Muir <engineering at mt.net>
To: time-nuts at febo.com
Sent: Thursday, 2 January 2014, 23:31
Subject: [time-nuts] Update on my previous note regarding NBS television timing reference experiment
I did a little digging and managed to find a paper on the original television time experiment which was authored by David Howe of NBS, now head of the Time and Frequency Metrology Group at NIST.? It can be found at http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=2&cad=rja&ved=0CDYQFjAB&url=http%3A%2F%2Fwww.researchgate.net%2Fpublication%2F3092613_Nationwide_Precise_Time_and_Frequency_Distribution_Utilizing_an_Active_Code_within_Network_Television_Broadcasts%2Ffile%2F9fcfd5089a1d534c56.pdf&ei=Ze_FUsrXJ-LsyQGY0oHYCw&usg=AFQjCNGw2wK-8_RYN98R_72AlRLcm2BAUA&bvm=bv.58187178,d.aWc(Google cached - whew!).
I stand corrected in my assumption that the timing signal was not related to the VITS interval in the video signal.? They actually were inserting the signal on line 1.? At the time Mr. Howe was involved in the development of the hardware that was deployed in the field for the experiment.? He stated that the received code provided unambiguous time to 12 hours, with a resolution of 1 nanosecond and long-term stability of 10 nanoseconds for 10-second averaging.
It's rather odd as to why I can't remember the sordid details off the top of my head regarding a project that took place 42 years ago....
Greg
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------------------------------
Message: 6
Date: Fri, 3 Jan 2014 09:04:10 -0000
From: "David J Taylor" <david-taylor at blueyonder.co.uk>
To: "Discussion of precise time and frequency measurement"
<time-nuts at febo.com>
Subject: Re: [time-nuts] Measuring TV delays
Message-ID: <D41F2731B4234019BFEBABADB9D940BA at Alta>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
reply-type=original
From: Chris Albertson
When they broadcast "live" TV like from a sports vent I wonder if the time
code generated by the camera is preserved? But then even if it were the
time might have been set manually to match the display on the camera
operator's cell phone.
Same for scenes with clacks in the background. Do you trust them to be
on-time? They might even have ben intentionally set wrong to hide the
transmit delay.
=================================
Can't comment on the camera time-code, Chris, but I would hope it was
centralised rather than being off the operator's phone!
The clocks I mentioned, F1 races, do appear to be accurate (observations
partially from being present at the event), and certainly /not/ skewed to
compensate for broadcast delay. Other times are when you see "behind the
scenes" and a control-room clock is visible. Usually these are centrally
synced, and can give a fair impression of the broadcast delays.
All this from UK television observations - and the programs don't have a
"bleep offensive content delay" - no nanny state here! (Others may differ
in that view - <G>) I recall what Alan Jones once called Michael Schumacher
on live TV, and the adjective was edited out on the repeat broadcast.
Cheers,
David
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu/
Email: david-taylor at blueyonder.co.uk
------------------------------
Message: 7
Date: Fri, 03 Jan 2014 13:28:04 +0100
From: Magnus Danielson <magnus at rubidium.dyndns.org>
To: time-nuts at febo.com
Subject: Re: [time-nuts] Measuring TV delays
Message-ID: <52C6ACD4.5060207 at rubidium.dyndns.org>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Bill,
On 02/01/14 20:33, Bill Hawkins wrote:
> IIRC, the reason why NTSC has an almost 30 fps rate is that early
> vacuum tube TV sets could develop heater-cathode leakage that
> would put a black "hum bar" in the picture. Almost 30 allows the
> bar to move through the picture in a 60 Hz power distribution
> system. Seems like Europe would have had that problem.
>
> No need for it now, but it's like the QWERTY keyboard . . .
Wouln't help that much, since the power-grids 60 Hz vary over more
frequency, than the 1/1.001 offset gives, which is about 59.94 Hz, and
over the coarse of a day it varies more than 60 mHz.
Cheers,
Magnus
------------------------------
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