Analog video sync

[bopstar]

Hi i would like to know how to get two analog video signals to be synced for a analog video mixer project, i have the basic understanding of what needs to be done but don't know which way to go. should i try using a phase lock loop or make a sync generator and add that to tape machine by modding a VCR to have a SYNC in to allow video mixing from two tape drives. and if so how do i do that

Kind Regards.

Justin Harris

[helius]

TV studios and editing suites have a "house black" that is generated from a master device, and then fed into a Distribution Amplifier to send out to all the various equipment that needs to be synchronized. The signal consists of completely black video with sync and (usually) colorburst. However, most equipment with sync in ports will allow any kind of CVBS signal to sync with, so you can simply use the video output of one device to synchronize others.

The kind of tape recorder used in these suites is called a VTR, and always has a sync (or Genlock) input. They are specifically designed to support online editing and mastering, with features like frame-accurate locate command and drop-in recording. I don't know if consumer VCRs could be modified to support genlock (seems unlikely), but they are still unsuitable for editing because they miss these other important features.

I would suggest reading some white papers from Leitch or Extron to see how video synchronization works in the real world and some of the issues involved.

[bopstar]

i knew all of that already i am asking how to mod preexisting vhs tape machines to do that (accept a house black)

[basinstreetdesign]

What you want to do is not impossible but none of your options are simple.

To hack a VCR to accept and use a house reference requires designing and building a complicated genlock circuit and frankensteining it into the VCR circuit.  This is probably the worst choice since it is so complex.  A properly locked system takes into account vertical and horizontal syncs as well as chroma sub-carrier phase lock.  I have built genlock systems and they generally turn out to be half a square foot of electronics (SMT, glue logic + PLLs + an FPGA + some non-trivial analog stuff, and that is if there is no uP).

Just using a simple PLL to align the motor of one VCR to the vertical sync pulse of another source is simpler but much more chancy.  For this you would need schematics of your machine and be able to understand in grisly detail how the circuit works and what ANY hack to it would do.  Even if you get the playback motional dynamics of the PLL+slave machine to be reasonably well-behaved, the result can still be out of phase by a few lines of video.  The sub-carrier phase will be random and constantly changing.  What would your mixer do in this situation?  I imagine the you would see half way through a wipe/dissolve one-half of the end picture is a stable source and the other half is jumping side-to-side with random/B&W colour.

Another possible solution is to put a Framestore Synchronizer between one source and the mixer and reference the FS to the second (now reference) source.  This is if you could find one.  The only FS I can find on EBAY is only USF$50 but is non-working.   It was made by Digital Processing Systems a company I knew quite well and who put out excellent stuff.  They don't exist anymore, having been absorbed by Leitch who were then absorbed by Harris.  A working one would still be relatively cheap (compared with new prices) these days now that analog video is effectively dead but you have to search more than I could do in 10 min.

Sorry to rain on your parade, and I hope I am not making too many assumptions about your situation but I wish I could be more help.

[drussell]

My Mitsubishi HS-U55 has edit connections on it to talk to other compatible VCRs to be able to do frame-accurate editing.  I've used it with other Mitsubishi and Electrohome VCRs before...  You can even drop one single frame into a recording without disturbing the adjacent frames. 

That was pretty darn nifty back in the day. 

I'm pretty sure it is a relatively simple signal on the edit jacks, all the fancy stuff is already in those higher-end model VCRs from that line.

[Siwastaja]

In the professional world, genlocking became a little bit "obsolete", or at least less necessary, once the digital frame stores came around in the early 1990's. They were hugely complex and expensive back then, but now the data rates for SD video are something a $100 smartphone technology could handle!

If you can't find one used, designing and building your own digital frame store would be probably a good choice. It's not easy either from scratch. But at least video ADC/DAC ICs do exist, and you can then interface them with an FPGA+SDRAM or even just a very capable microcontroller with DMA.

This way, at least the result would be least iffy, giving perfect mixing, and most widely usable, with any equipment working without modifications. When you have the basics designed, it would be fairly trivial to add things like frame rate / color system conversions (PAL-NTSC) (and all those nice digital effects you can play around but don't actually want).

[John Heath]

There could be some hope in an up scale used video mixing board used by DJs and such. In order to fade from one video to the next the two videos had to be in phase for it to look right . A ton of electronic horse power went into this to take two different videos out of phase and possibly not the same format , pal ntsc , and knit them together into one video with a band width of 10 MHz.  No easy task. If you snoop around maybe you can buy one of these video mixing boards used.

[james_s]

The Video Toaster was an incredibly popular bit of hardware back in the analog video days, once you see the various mix, wipe and fade effects you'll start to notice them in all sorts of 80s stuff. The hardware is not particularly rare, but since it's Amiga based it's almost never cheap.

[John Heath]

Speaking of this I remember repairing a karaoke machine. It was some minor problem. The interesting part was the ability to change the key to sing in. If the song was in D but you are more comfortable singing in C then you change the song to the key of key to C. The odd part was a 2 minute song in D was still a 2 minute song in C . You see the problem. In order to change a song from key D to C it had to be longer than 2 minutes but in both cases the song was still 2 minutes long. To this day I still do not know how they did this? The whole song was frequency synthesizers ?

[bopstar]

I find your respond quite weird as in the 70s analog colour video syncing was a thing that was done all analog. no digital TBS was needed just delay lines and phase lock loops

[bopstar]

i love the video toaster

[james_s]

Many audio editing programs allow changing the pitch and speed independently. I've never actually looked into how these features work but they do. I suspect they break the sound down into small portions and then insert copies of these portions or remove bits at regular intervals to adjust the length independent of the pitch. Audacity is the software I have, it's free and I believe open source so technically you could find out.

[BrianHG]

Many audio editing programs allow changing the pitch and speed independently. I've never actually looked into how these features work but they do. I suspect they break the sound down into small portions and then insert copies of these portions or remove bits at regular intervals to adjust the length independent of the pitch. Audacity is the software I have, it's free and I believe open source so technically you could find out.

For most tempo changing audio tools, like the DSP ones in Audacity, you got it correct as patents on this technique have expired in the early 2000s.
For the rare FFT deconstruct/reconstruct super high quality ones, valid patents still exist, but not for much longer....

[BrianHG]

I find your respond quite weird as in the 70s analog colour video syncing was a thing that was done all analog. no digital TBS was needed just delay lines and phase lock loops

In the 70s, the color analog mixing was done in YUV component analog, or, for rare blue-screen tricks like for weathermen map backdrop, it was done in RGB analog.  The precision of the chroma sub-carrier was not necessary as the final full NTSC signal with the chroma was done last after the mixing console mixed all the primary video sources, with slight jitter and alignment error of each one, then superimposed a clean sync and constructed the clean full chroma mixed signal.

There also existed an analog video warp and blending device, but this was done with small displays & a camera in front.  See here: (Don't dream of achieving this on your own and unlike the toaster, there were no square chunks....)

[bopstar]

I know about the Scanimate and i did make a small scale version of it using an old rear projection crt a driver board design from google and a high resolution black and white CCTV camera

[John Heath]

Many audio editing programs allow changing the pitch and speed independently. I've never actually looked into how these features work but they do. I suspect they break the sound down into small portions and then insert copies of these portions or remove bits at regular intervals to adjust the length independent of the pitch. Audacity is the software I have, it's free and I believe open source so technically you could find out.

For most tempo changing audio tools, like the DSP ones in Audacity, you got it correct as patents on this technique have expired in the early 2000s.
For the rare FFT deconstruct/reconstruct super high quality ones, valid patents still exist, but not for much longer....

FFT deconstruct then reconstruct. This is interesting. Done this way the the length of the song and the pitch of the song are separate issues. The song could be in any key but always be 2 minutes in length. I wonder how careless you could be with the exact FFT shape and still get away with it? From 10 Hz to 10 KHz would you need 10,000 samples of the FFT for a given slice of time or could you get away with 1000 samples?

[John Heath]

I find your respond quite weird as in the 70s analog colour video syncing was a thing that was done all analog. no digital TBS was needed just delay lines and phase lock loops

In the 70s, the color analog mixing was done in YUV component analog, or, for rare blue-screen tricks like for weathermen map backdrop, it was done in RGB analog.  The precision of the chroma sub-carrier was not necessary as the final full NTSC signal with the chroma was done last after the mixing console mixed all the primary video sources, with slight jitter and alignment error of each one, then superimposed a clean sync and constructed the clean full chroma mixed signal.

There also existed an analog video warp and blending device, but this was done with small displays & a camera in front.  See here: (Don't dream of achieving this on your own and unlike the toaster, there were no square chunks....)

I liked that video. A throw away society. It bring to mind the  day they stopped all analog TV to go digital. In one day at the stroke of midnight millions of TVs became obsolete. Thousands of clock repairmen without clocks to fix.

[james_s]

I suspect hardly anybody uses the digital OTA broadcasts either, certainly nobody I know does, a surpring number of people don't even realize you can receive HD using an antenna.

At least converter boxes were available cheaply. I got one shortly after the changeover and connected it to the XBR Trinitron downstairs. I marveled over the stunning picture quality a few times then quickly realized there is nothing but garbage on TV anyway and by then all the channels had those distracting logos plastered permanently in the corner which IMO makes them unwatchable.

[BradC]

I marveled over the stunning picture quality a few times then quickly realized there is nothing but garbage on TV anyway

Yes, but it's the best quality garbage you've ever seen!

[dexters_lab]

Hi i would like to know how to get two analog video signals to be synced for a analog video mixer project, i have the basic understanding of what needs to be done but don't know which way to go. should i try using a phase lock loop or make a sync generator and add that to tape machine by modding a VCR to have a SYNC in to allow video mixing from two tape drives. and if so how do i do that

Kind Regards.

Justin Harris

as others have said, this really isn't possible with a domestic VCR

syncing two analog video sources is complex, especially if the source is tape

It's best done digitally with a 'framestore', where multiple inputs are digitized, combined and then output as a single video channel. Quantel did this in 1975 for TV production with the DFS-3000

i'd recommend just sourcing a cheap video mixer off ebay which will do this, i'd bet they are cheap as chips now and you'll save yourself a whole load of pain

[bopstar]

i enjoy the pain. plus i love learning about analog TTL logic. and fine ill be intrested in learning about frame stores. just please let me know where i can learn about those. also i cannot afford a any of the old video mixers of ebay. i am so poor i get all my chips from companies who are converting for DIP/through hole to SMD as liquidated stock and heaps of free sample chips from TI, Microchip, Analog Deceives etc

[james_s]

"Analog TTL logic" is a contradiction. TTL logic is digital.

[Alex Eisenhut]

i enjoy the pain. plus i love learning about analog TTL logic. and fine ill be intrested in learning about frame stores. just please let me know where i can learn about those. also i cannot afford a any of the old video mixers of ebay. i am so poor i get all my chips from companies who are converting for DIP/through hole to SMD as liquidated stock and heaps of free sample chips from TI, Microchip, Analog Deceives etc

Well, fine, but why focus on this obsolete yet tremendously complex domain?

A VIC-20 would be helpful as it outputs NTSC/PAL video natively and can be put into interlace mode.

A university library will have many textbooks on obsolete stuff like video production. I used to hang out at Concordia University just to browse 1960s textbooks and occasional databook.

[bopstar]

as stated i cannot afford to use modern technology and thus must use what i have and what i have is old analog equipment which in my case i wish to use to learn what i can about Analog Video. instead of just saying its to hard or ether impossible (which i know for a fact is not the case) tell me where i can learn more e.g. books, pdfs any schematic. lets forget about the VCR syncing and more to camera syncing. i make my own analog cameras with cheap CCTV modules.

example of module:

https://www.aliexpress.com/item/New-HD-700TVL-FPV-Mini-Analog-Camera-DC12V-CCTV-Home-Security-Video-Camera-with-Mic/32849564321.html?spm=2114.search0104.3.36.2bb48164Q8NWXT&ws_ab_test=searchweb0_0,searchweb201602_5_10065_10344_10068_10130_10342_10547_10343_10340_10548_10341_10084_10617_10616_10083_10618_10615_10307_10131_10132_5920012_10133_10313_10059_10534_100031_10103_441_10624_442_10623_10622_10621_10620_10142,searchweb201603_40,ppcSwitch_3&algo_expid=85e845c4-9f5b-47b2-ab03-30373873759a-8&algo_pvid=85e845c4-9f5b-47b2-ab03-30373873759a&priceBeautifyAB=3

[james_s]

Faced with that situation, I would be looking for used professional VCRs, I'm sure most of them have been junked by now but I'm sure there must be some sitting in storage rooms and surplus stores from all the analog TV stations that went offline.