The Grass Valley 9500 sync generator change over was as close to failure proof as you could get. They had a PC board with glass reed relays in a circle forming a 6 pole double pole switch. There were no buffers or any active components in the signal path, just the glass relays. They did monitor all six signals from both sync generators for amplitude. A loss on any signal would trigger a solenoid to move a permanent magnet disc under the reed relay board to switch to the standby generator. To manually switch there was a lever to move the magnet disc to enable either sync generator. So even if the changeover unit had a power failure, you could still easily manually switch to the opposite sync generator. A bit overkill, it's only TV! The Tektronix and Leitch changeover units of the day were active devices like the Phillips.
Hello. 40 years ago, I was an engineer of ITE test pattern generators for NTSC, PAL, SECAM, etc. This brought back fond memories of the past. Thank you!
Note that in consumer and pro non broadcast VTRs (Umatic) the color subcarrier is not locked to H unless you use a TBC. This does produce a decent image but is also introduces artifacts as the chroma is stabilized but not the luminance signal. You can forget about consistent Y/C delay! Also note that in the USA early 2in quad color videotape broadcasts also had unlocked subcarrier as they had no way to stabilize the luminance to the required precision for color playback. Two processes were used. RCA hetrodyned the separated chroma up to a higher frequency around 20mhz, then back down to 3.58 and used the off tape burst to cancel out the chroma jitter. Ampex took a different approach. They demodulated the chroma to R-Y/B-Y using the off tape burst, then re-modulated using station subcarrier or a local free running oscillator. This was technically not a legal broadcast NTSC signal but the American FCC looked the other way as this was the best technology could offer at the time. Around 1960 Bob Coleman of WBBM TV developed the prototype AMTEC and COLORTEC which was an analog TBC that provided phase locked direct color playback. But it took until 1974 where digital technology became available to timebase correct helical VTRs. There were a few high end direct NTSC color recording helical VTRs that did have analog TBCs, the IVC 9000, Ampex 7900, Sony MV 10000, but they never took off in the broadcast arena until type C came around. What was revolutionary however with the early digital TBCs was the ability to make 3/4inch Umatic VTRs meet broadcast standards and killed film as the defacto news gathering technology.
I've long knew that you can mix synchronized composite feeds with essentially just a potentiometer, but it's still quite magical to see it happen live. It would be also nice to see it done purposefully wrong, on signals that can't be mixed. Like SECAM - and see how that would manifest on screen. I have an idea of what the result would be, I can also simulate that in software (or generate a "fake" SECAM signal on a Raspberry Pi or something) but seeing that done with real studio equipment would be something else ;)
Happened to work a bit on an SPG design that never materialised to a real product. Note, many current day broadcast engineers won't know anything about the PAL 8 field sequence, so a good mention! These bi-level syncs are still used, though more and more they're replaced in studios by PTP in networked video. There was a brief use of tri-level sync for HD, but most facilities just kept using the bi-level syncs, also for HD.
I actually tried a similar thing a week ago using 2 Blackmagic Ultrastudio 4K units. They're genlockable so I sync'ed them and had them output to a Karl Klomp Dirty video mixer. I had the same result as you with the fade being scratchy. But believe it or not I actually have a use for all this with modular analog glitch video gear like that from Syntonie in France. Basically I can output one video feed and then have another synced feed functioning as control voltage on the first. This lets the CV feed function as a mask/key for whatever glitch effect is being applied.
BTW if you don't have a vectorscope, but you want to compare phases you might be able to do this in XY-mode on some digital oscilloscopes. Essentially you need to trigger in such a way that the bursts fill out the capture buffer of the oscilloscope. This will then be used to draw the image in XY-mode. It essentially gives you a "gated XY-mode".
Trivia time Matt - back in the day the studios at channel 7 Sydney were not gen locked to presentation. They were close... but not quite enough to give a clean fade-up from black reference to the selected studio in full colour (you'd get that usual B&W picture and then colour reference would kick in at the top of the fade). So it was just common practice for pres to face to black off the commercial break for example, cut the studio to line (a clean cut), then the studio would fade up instead (the reverse when going to a break,). Why didn't they fix it? Dunno 😉😂. Timing every source back then would have be quite cost prohibited. Unless a frame store was available and free at the time, OBs were in the same situation frequently. Fun times...! Great vid BTW, cheers.
@@dogbreaththe3rd851 So right indeed! In fact, as a no joke, the small studio with a camera that we had attached to presentation for back announcements was timed using a large cable reel tucked away in the back corner. When I first started at 17 I asked what the cable was for and instead of a correct explanation I was told _"If you ever touch that roll of cable, you'll be sacked!"_ Shortly afterwards I understood why - quite scary at that age 🥴
Prior to the 1990s you would have need an individual SPG for each BB where a differing timing was required. With each unit costing thousands of dollars it is possible it was a commercial trade-off.
thx for clearing my confusion with those external sync generators! i was thinking how do they work with properly lining up video... wonder what are those aja patterns built in...
Ohh there's a neat story about the first official PAL broadcast which can be found here: th-cam.com/video/lgO34-6QLEw/w-d-xo.html Apparently the sync pulse generator broke in a subtile way, messing up the phase relation between sync pulses and the chroma subcarrier. At first nobody noticed, after all all monitors were showing perfect images, but when they played back the tape it was all in monochrome. Apparently also the BBC, which somehow got the signal, too, called to complain about the issue. BTW the engineer flipping the switch couldn't see a monitor when reaching for it... so he flipped it a bit to early.
I remember when I got my first oscilloscope that the chroma burst always was in 2 phases on every channel I've checked. Back then I thought that would be normal. Could it be that some stations operated with a slightly different subcarrier frequency (off by 25 Hz to turn the 8V sequence into a 4V sequence)? This was in the early 1990s on satellite channels.
Also what I've noticed is that ZDF has at least one cartoon show "Alfred J. Kwak" shown from 1990-1993 which on re-runs has a problem of the saturation flickering like wild. Could this be caused by the station switching between subcarrier frequencies between the original run and the digitization?
1:56 - Now I'm confused. I assume that if the grid needs more power the dynamos have to rotate faster? Thus higher Hz? This isn't common knowledge. But what about a dynamo with no load? Where does the energy go? 🏥 🛏 💊
If more electric power is required the energy driving the generator is increased which make it TRY to speed up but that causes the generators phase to try to advance which causes the current feeding the grid to increase using up the added energy. The generator thus stays synchronized to the grid but delivers more energy to the grid. If the generator is not connected to a load the generators speed of coarse increases to use up any added energy feeding the generator.
The Grass Valley 9500 sync generator change over was as close to failure proof as you could get. They had a PC board with glass reed relays in a circle forming a 6 pole double pole switch. There were no buffers or any active components in the signal path, just the glass relays. They did monitor all six signals from both sync generators for amplitude. A loss on any signal would trigger a solenoid to move a permanent magnet disc under the reed relay board to switch to the standby generator. To manually switch there was a lever to move the magnet disc to enable either sync generator. So even if the changeover unit had a power failure, you could still easily manually switch to the opposite sync generator. A bit overkill, it's only TV! The Tektronix and Leitch changeover units of the day were active devices like the Phillips.
Hello. 40 years ago, I was an engineer of ITE test pattern generators for NTSC, PAL, SECAM, etc.
This brought back fond memories of the past.
Thank you!
Note that in consumer and pro non broadcast VTRs (Umatic) the color subcarrier is not locked to H unless you use a TBC. This does produce a decent image but is also introduces artifacts as the chroma is stabilized but not the luminance signal. You can forget about consistent Y/C delay! Also note that in the USA early 2in quad color videotape broadcasts also had unlocked subcarrier as they had no way to stabilize the luminance to the required precision for color playback. Two processes were used. RCA hetrodyned the separated chroma up to a higher frequency around 20mhz, then back down to 3.58 and used the off tape burst to cancel out the chroma jitter. Ampex took a different approach. They demodulated the chroma to R-Y/B-Y using the off tape burst, then re-modulated using station subcarrier or a local free running oscillator. This was technically not a legal broadcast NTSC signal but the American FCC looked the other way as this was the best technology could offer at the time. Around 1960 Bob Coleman of WBBM TV developed the prototype AMTEC and COLORTEC which was an analog TBC that provided phase locked direct color playback. But it took until 1974 where digital technology became available to timebase correct helical VTRs. There were a few high end direct NTSC color recording helical VTRs that did have analog TBCs, the IVC 9000, Ampex 7900, Sony MV 10000, but they never took off in the broadcast arena until type C came around. What was revolutionary however with the early digital TBCs was the ability to make 3/4inch Umatic VTRs meet broadcast standards and killed film as the defacto news gathering technology.
Always amazing technical info and detail!
The quest is answered! Thank you!!!
I've long knew that you can mix synchronized composite feeds with essentially just a potentiometer, but it's still quite magical to see it happen live.
It would be also nice to see it done purposefully wrong, on signals that can't be mixed. Like SECAM - and see how that would manifest on screen. I have an idea of what the result would be, I can also simulate that in software (or generate a "fake" SECAM signal on a Raspberry Pi or something) but seeing that done with real studio equipment would be something else ;)
Happened to work a bit on an SPG design that never materialised to a real product. Note, many current day broadcast engineers won't know anything about the PAL 8 field sequence, so a good mention! These bi-level syncs are still used, though more and more they're replaced in studios by PTP in networked video. There was a brief use of tri-level sync for HD, but most facilities just kept using the bi-level syncs, also for HD.
Thanking you most kindly
Very interesting Matt!
I actually tried a similar thing a week ago using 2 Blackmagic Ultrastudio 4K units. They're genlockable so I sync'ed them and had them output to a Karl Klomp Dirty video mixer. I had the same result as you with the fade being scratchy. But believe it or not I actually have a use for all this with modular analog glitch video gear like that from Syntonie in France. Basically I can output one video feed and then have another synced feed functioning as control voltage on the first. This lets the CV feed function as a mask/key for whatever glitch effect is being applied.
Very interesting video, thanks. Maybe in the future a video on the 8-field PAL sequence? Analog Color encoding is wildly complex.
Would be interesting but I think that would test the patience of a TH-cam audience beyond breaking point!
@@mattstvbarn This is the Internet, people listen to 4+ hour podcasts regularly. There is no reason to think the 2:30 rule applies here.
Nice overview 😊
BTW if you don't have a vectorscope, but you want to compare phases you might be able to do this in XY-mode on some digital oscilloscopes. Essentially you need to trigger in such a way that the bursts fill out the capture buffer of the oscilloscope. This will then be used to draw the image in XY-mode. It essentially gives you a "gated XY-mode".
Great info thank you!
Trivia time Matt - back in the day the studios at channel 7 Sydney were not gen locked to presentation. They were close... but not quite enough to give a clean fade-up from black reference to the selected studio in full colour (you'd get that usual B&W picture and then colour reference would kick in at the top of the fade). So it was just common practice for pres to face to black off the commercial break for example, cut the studio to line (a clean cut), then the studio would fade up instead (the reverse when going to a break,). Why didn't they fix it? Dunno 😉😂. Timing every source back then would have be quite cost prohibited. Unless a frame store was available and free at the time, OBs were in the same situation frequently. Fun times...! Great vid BTW, cheers.
@@dogbreaththe3rd851 So right indeed! In fact, as a no joke, the small studio with a camera that we had attached to presentation for back announcements was timed using a large cable reel tucked away in the back corner. When I first started at 17 I asked what the cable was for and instead of a correct explanation I was told _"If you ever touch that roll of cable, you'll be sacked!"_ Shortly afterwards I understood why - quite scary at that age 🥴
Prior to the 1990s you would have need an individual SPG for each BB where a differing timing was required. With each unit costing thousands of dollars it is possible it was a commercial trade-off.
@@dogbreaththe3rd851 sure, but there comes a point when delaying with cables would become impractical!
thx for clearing my confusion with those external sync generators! i was thinking how do they work with properly lining up video... wonder what are those aja patterns built in...
SPG - not just the name of Vyvyan's pet hamster in The Young Ones...
Ohh there's a neat story about the first official PAL broadcast which can be found here:
th-cam.com/video/lgO34-6QLEw/w-d-xo.html
Apparently the sync pulse generator broke in a subtile way, messing up the phase relation between sync pulses and the chroma subcarrier. At first nobody noticed, after all all monitors were showing perfect images, but when they played back the tape it was all in monochrome. Apparently also the BBC, which somehow got the signal, too, called to complain about the issue.
BTW the engineer flipping the switch couldn't see a monitor when reaching for it... so he flipped it a bit to early.
Hi, Matt . Great video. Can you film detailed secam explanation with oscillograms , please. ? I know, there is one , but it too short , unfortunately.
I remember when I got my first oscilloscope that the chroma burst always was in 2 phases on every channel I've checked. Back then I thought that would be normal. Could it be that some stations operated with a slightly different subcarrier frequency (off by 25 Hz to turn the 8V sequence into a 4V sequence)? This was in the early 1990s on satellite channels.
Also what I've noticed is that ZDF has at least one cartoon show "Alfred J. Kwak" shown from 1990-1993 which on re-runs has a problem of the saturation flickering like wild. Could this be caused by the station switching between subcarrier frequencies between the original run and the digitization?
1:56 - Now I'm confused. I assume that if the grid needs more power the dynamos have to rotate faster? Thus higher Hz? This isn't common knowledge. But what about a dynamo with no load? Where does the energy go? 🏥 🛏 💊
If more electric power is required the energy driving the generator is increased which make it TRY to speed up but that causes the generators phase to try to advance which causes the current feeding the grid to increase using up the added energy. The generator thus stays synchronized to the grid but delivers more energy to the grid. If the generator is not connected to a load the generators speed of coarse increases to use up any added energy feeding the generator.