What about Tri-Level Sync?

[SDAmatuer]

Hello all

I'm new to the Forum and also a little new to the world of Post Audio. I'm looking for some info on professional equipment. Specifically at the moment I'm looking for info on a Tri-Level Sync. Exactly what it is and how it works. I did a search but everyone talking about it is already familiar with the basics of it, so that doesn't help me too much, seeing as i don't know anything at all about what they do. Thanks!

[Thomas W. Bethe]

A couple of places to look at.

Video signal generator - Wikipedia, the free encyclopedia

HD CINEMA: Time Code and HD cameras

Extron Electronics - Tri-Level Sync in a Bi-Level World

Hope this helps...

[SDAmatuer]

Thanks for those links. I've looked at those before, but they just make my head swim. I think I just need to get a consultant to sit down with me and go over the plans and lay out everything i need, cause i feel like i'm trying to re-invent the wheel here.

[hociman]

Originally Posted by SDAmatuer

Specifically at the moment I'm looking for info on a Tri-Level Sync. Exactly what it is and how it works.

The Extron article goes to a lower level in terms of what tri-level sync is and how it works. I think you may just want a higher level overview of what it is and how it works.

Tri-level sync is to HDTV (ATSC) as bi-level sync is to SDTV (NTSC). Within their respective standards, they each serve the same purpose. That purpose is to mark when a frame of video starts, and by doing so infinitely, convey the speed of the video being played. Why is it important to know when a frame of video starts? Without knowing this, any edit operation you try to perform will be suspect and best and just not work at worst.

Another way to think about tri-level sync is in the context of multiple musicians playing to the same tempo. If you tell two (2) musicians to play at a tempo of quarter note = 120bpm, they can each set their metronomes to that tempo and start playing. The problem with this is that each metronome does not know of the existence of the other metronome, so while both players will be playing at the same speed (quarter note = 120bpm), they will not be at the same position (same beat). So you have two players playing at the same tempo, but their downbeats never line up. If you use one (1) metronome for both players, now they are both going to be playing at the same tempo, and their downbeats will always match.

Let's take this analogy to HDTV (ATSC). If you have two devices working at 1080p/23.98, and neither device knows of the other's existence, they will each operate at 23.98, but their frame edges will never line up. A tri-level sync generator will now serve the purpose of the single metronome from earlier. The output of the tri-level sync generator will be sent to the HD sync inputs of both devices. Now both devices will operate at 23.98, and their frame edges will line up.

I cannot think of another way to describe what tri-level is and how it works without getting into some electronics theory. If that's what you want though, let us know and perhaps we can point you in a different direction.

[SDAmatuer]

Ok, that makes sense. So in this case, the two devices that are playing at the 23.98 would be the computer with the PT session and tape deck that has the video, right?

Sorry for the ignorant questions, I just want to wrap my head around this.

[hociman]

Originally Posted by SDAmatuer

Ok, that makes sense. So in this case, the two devices that are playing at the 23.98 would be the computer with the PT session and tape deck that has the video, right?

Correct. Without a common tri-level sync reference for both Pro Tools and the VTR (tape deck), they will both play, but not at the same speed.

Let's expand upon this a bit. In the case of Pro Tools, you will have to be using an HD system, and if you want to truly lock it to 23.98, you will need a SYNC HD peripheral. You would connect one 1080p/23.98 output of your tri-level sync generator to the video ref input of the SYNC HD, and the other 1080p/23.98 output of your tri-level sync generator would be connected to the HD video ref input of the VTR.

If your tri-level sync generator only has one (1) output, you can use a composite video DA (distribution amplifier) to create the two (2) outputs for the SYNC HD and VTR video ref inputs.

[jimlongo]

Can you tell me why you can't lock HD video with a Sync /IO and blackburst?
And furthermore what hardware is required?

Thanks.

[georgia]

SD and HD are 2 different standards. They require two different types of sync.

SD bi-sync and HD tri-sync are different signals.

SD Bi-sync supports computer video, composite video, s-video, and component video, by using 2 voltage levels ( high and low )... systems using bi-syn are triggered by the differential voltage at the leading ( negative) edge of the signal. Bi-sync basically runs at 0 votage ( black) then drops to a negative voltage and then back to zero ( 2 states or BI-sync)

Tri-sync provides a more exacting sync for the 3 component signals. HD has sync info on all three channels ( Y, Pb, and Pr). Tri sync starts at 0 volts ( video black ) then goes negitive, then a positive voltage, then back to 0 volts ( 3 states, Tri-Sync). This also fixed the introduction of a voltage differential by bi-sync signals into the actual video signal. the tri-sync signal is triggered by the on the negative transition, then on the positive transition. thus 0,-300mv,+300mv,0 3 sync points... This all happens in the Horizontal blanking interval. There is something called the White reference level that is set at 700mv. the 700mv drops to 0 at the start of the blanking period. the signal drops to -300mv, the to +300mv, then to 0 the back to reference white 700mv. This is the HD Analog horizontal timing data where HD tri-level sync is used. ( I don't remember what the white level is for bi-sync.. sorry pulling most of this out of my head... ) There are also a couple of issues revolving around the Progressive vs interlaced HD frame timing that comes into play here.

bi-sync is on the Y-signal on SD video. tri-sync is on all 3 channels for HD. ( check out SMPTE 274M ad SMPTE 296M )

so the two are incompatable for sync .. there are a lot of options out there for devices that support both bi-sync and tri-sync.

the sync IO accepts SD BiSync or "traditional" video black, the HDSync IO accepts Tri-sync signals. As far as gear it all depends on what you are syncing... if its protools to an HD video deck and you are laying back audio, you can use a tri-sync box that offers bi-sync. The bisync can be routed to the protools rig and the tri-sync can be used for the HD deck. If you are dealing with laying back an HD video signal from a video editing system with an AJA Kona3 card to an HD video deck directly connected, you don't need
a tri-sync gen, becuase the AJA kone3 offers this to the deck via the video signal (read the Kona3 card for details, i don't remember exactly how they do it, but they do) if you are using a euphonix system 5 HDMI IO and a HD video deck you need a tri-sync generator. So it all depends on what you are trying to sync.

I hope this helps a bit with some of the tech background.
cheers
geo

[TVPostSound]

Can you tell me why you can't lock HD video with a Sync /IO and blackburst?
And furthermore what hardware is required?

You can if the online editor keeps the TC at 29.97.


Around $300, great thing to have:

GEN10 - AJA Video - Serial Digital Video Interface and Conversion



















.

[Big Andy]

Unless you're doing Dolby E encoding....I don't really think you need one.

I may get bashed for making that statement tho.

[jimlongo]

Originally Posted by Big Andy

Unless you're doing Dolby E encoding....I don't really think you need one.

Since I don't have any tape machines, I'm wondering if I would need it or not. Just looking down the road to Video Satellite with an HD capable card playing QuickTime movies - and guaranteeing consistent sync frame edge sync.

[JoeMilner]

I use the Aja Gen-10 as well, but with a standard Sync IO. Cool thing about the Gen-10 is that it outputs both tri-level and black simultaneously, so the PT system gets black and the Aja Kona LH (playing HD QTs on VVTR) gets tri-level. Works a treat

[jimlongo]

I use the Aja Gen-10 as well, but with a standard Sync IO

Is there a non-standard Sync I/O?

[minister]

Originally Posted by jimlongo

Is there a non-standard Sync I/O?

SYNC HD I/O.

SYNC HD

[JoeMilner]

And I learned about the Gen-10 from Tom Hambleton

[hociman]

Originally Posted by jimlongo

Just looking down the road to Video Satellite with an HD capable card playing QuickTime movies - and guaranteeing consistent sync frame edge sync.

The foolproof way to set this up would be to use the appropriate tri-level reference and route it to the Video Satellite and the Pro Tools system, both of which would have a SYNC HD. If you are working with an HD format that isn't 1080p/23.98, you may be able to use bi-level sync and make it work. It becomes a question of whether or not Pro Tools has been programmed to be finicky about the video reference. If its programmed such that it will only lock to HD ref for HD frame rates, then you will have no choice.

[jhg]

Originally Posted by Big Andy

Unless you're doing Dolby E encoding....I don't really think you need one.

I may get bashed for making that statement tho.

If you're doing Dolby E at 23.98 you will need a DP579 trilevel sync interface to create Dolby black that the E encoder/decoder use.

[Big Andy]

Exactly....to the above....and in addition, if you do happen to do Dolby E prints, you will also need a DA-98 recorder as the encoded info is printed as 20 bit. EXPENSIVE process.

[hociman]

Originally Posted by Big Andy

Exactly....to the above....and in addition, if you do happen to do Dolby E prints, you will also need a DA-98 recorder as the encoded info is printed as 20 bit. EXPENSIVE process.

Why would anyone print Dolby E to a DTRS tape?

[georgia]

Originally Posted by hociman

Why would anyone print Dolby E to a DTRS tape?

I was just going to ask that...


cheers
geo

[brianroth]

I ran across this thread when researching a problem I encountered with the Aja GEN10. The system in question is a new, small-ish studio that produces a live, 1 hour daily news magazine that is streamed on the net and simulcast on Cox cable in their Oklahoma markets. The majority of the plant is 1080i (with Aja FS-1 "Swiss Army Knife" boxes to input/output from/to some legacy analog equipment that was recycled from the older analog facility).

The bulk of the equipment requires tri-level sync, but there are some units that require blackburst. Hence, the GEN10 appeared to be an inexpensive answer for all "house sync" requirements.

In addition to new HD cameras on floor pedestals, we included a pair of Panasonic AW-HE100 cameras mounted from the lighting grid to supply wide shots, etc. The HE100's are self-contained "robo cams" (with remote controlled pan/tilt/zoom/focus) which come standard with analog outputs, BUT have an optional 1080i output module which we purchased for each cam.

The HE100's require blackburst sync.

When we heated up the new system earlier this week, we were stunned to see that the HE100's were vertically offset about 1/3 of a frame. IOW, the image from those cams...while horizontally synced...was almost split in half with a black bar in the "middle".

I connected my dual trace Tek scope to the outputs of the trilevel DAs and the blackburst DAs, and after some fiddling with triggering, etc. observed the vertical sync "retrace" "blanking" pulses were indeed offset between the trilevel and blackburst signals.

Thinking that we had a defective GEN10, we contacted Aja tech support. They checked with Engineering, and reported back that the trilevel and blackburst outputs ARE NOT VERTICALLY TIMED with each other!!!!

We did a quick "search and scramble" and overnighted:

DV-321 Genlockable HD/SD Sync Generator

Functionally the same as a GEN10, but with Genlock input...which I wanted from the beginning "just in case" for some odd-ball future requirement. ESE also has:

DV-319 HD/SD Sync Generator

...wiithout genlock.

Sync problem solved for a few more bucks!

I am annoyed that Aja makes NO mention of the non-timed Vertical in any of their GEN10 sales docs, nor in the tech/install manual. Live And Learn! That said, I generally like Aja products.

Bri

PS...last year I discovered that the analog outputs of the Aja FS-1 units we bought for another project had a volt or so of DC offset; that caused some problems with devices which had DC coupled inputs....."blown out" analog video. I fixed that problem by installing a low impedance 1000 microfarad capacitor in-line. Aja tech support is aware of that problem, and it may be fixed by now.

I still like Aja....

[rhumphries]

Thank you, Brian. That is good to know.

-Richard