Dual Visual Cortex synchronization troubleshooting

I just installed a second Visual Cortex in my rig. They both perform fine, but when I send data from one VC’s input decoder to the other VC’s Channel A or B inputs I get a scrolling image.

Please help :sob:

It looks like you need to connect sync between the two units. Two ways to do this.

One of them is to use the frontpanel connections… just patch a video out from the “master” cortex into the Y jack of the second unit’s Input Decoder section. You should see the little lock icon light up on the second unit and now be able to patch between the two.

The more dedicated way is to connect them in the rear. The Sync output jack of the master unit goes to the Sync Input jack of the slaved unit. You then need to flip the switch for sync source (directly above the sync input jack) to the lower position (nearest the jack.)

The low profile RCA cables we sell at LZX are designed for making these connections in a shallow case, but any RCA cable will do. Try to keep the connection short if you can.


Thanks Lars.

I have tried what you mentioned and nothing seems to be working.

Using an RCA to sync on the front panel appears to slow the scrolling a little but it’s still there. This also begins mixing the two cortex’ in a way I don’t want.

I take it both Genlock sources should be in a down position? I have actually tried all combinations possible here without any luck.

I am using a short RCA underneath. Also tried swapping Master and Slave relationship. Both cortex’ appear to be functioning perfectly, it’s just when I try to mix the two as mentioned in the opening question.

I am really hoping there may be something else I can try. I have the Video Sync Distribution Cable if that can be useful here? What about the Colour time Base Corrector, could that help?

Thanks in advance


What about if you just patch the ramp outputs from one cortex to another? (Don’t use the input decoder or an external source.) We need to rule out that your external source is having trouble locking first. Is the green lock LED turning on when you have one Cortex slaved to the other?

I had mixed results so I went through some combinations. Nothing allowed me to send video from one input decoder to the other cortex’ inputs without scrolling.

I probably didn’t need to change the Gen Lock switch as much as I did but it helped with an elimination process.

With the master and slave cortex’ gen locks both down, the master cortex sync LED is red, while the slave’s is clear (off). Typical video connections scroll on both cortex’, and also scroll when sending video to each other. Typical ramp connections and ramp connections between the two cortex’ were all stable.

With the master cortex gen lock up, and the slave’s down, the master cortex sync LED is green, while the slave’s is clear (off). Typical video connections on the master produce stable video, while the slave is scrolling here. Video connections between the two cortex are all scrolling. Typical ramp connections are stable here, but are scrolling when sent to the other cortex.

With the master and slave cortex’ gen locks both up, both sync LEDs are green. Typical video connections are stable here, but scrolling when sent to the other cortex. Ramps produce the same behaviour.

With the master gen lock down and the slave’s up, the master sync LED is red, and the slave’s is green. Typical video connections on the master are scrolling, and stable on the slave. Video connections from the master to the slave are scrolling, but from the slave to the master are not scrolling. Typical ramps and ramps between the two cortex’ are all stable here.

Thanks, hope that helps! :slightly_smiling_face:

@Travis I’m pretty confused. Are all these examples with external video sources disconnected entirely? What video output are you using and what are you displaying it on?

Try this test:

  • No external video connections/source.
  • Sync out on Cortex #1 should go to sync in on Cortex #2
  • The genlock switch on Cortex #2 should be in its down position (nearest the rear RCA jack)
  • The position of the switch on Cortex #1 doesn’t matter for this test
  • You should see the lock LED light up on Cortex #2 but not Cortex #1.
  • Monitor the video output of Cortex #2.
  • Patch ramps from Cortex #2 to its own inputs. Should be stable.
  • Patch ramps from Cortex #1 to Cortex #2’s inputs. Should be stable.
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Sorry I was unsure about the gen locks so it got a bit convoluted. I had video connected on both cortex with those tests. One is an output from my computer and the other is a live feed from a camera if that’s worth noting.

I’m using the composite outputs of the cortex’ and using a CRT TV and a basic monitor to display.

Following the test above, the master cortex lock LED is off while the slaves is red, not green. All combinations of ramps were stable.

Also tested the “…video out from the “master” cortex into the Y jack of the second unit’s Input Decoder section” with this configuration with the same LED states and got a scrolling image when connecting video, but sending a ramp was stable.

I’m using very short RCAs and already tried replacing the one I’m using here.

OK, I think this issue is related to a basic misunderstanding about how video sync/genlock works.

Short answer: You can’t send 2x external video sources into 2x Cortex modules, and then synchronize the outputs. You need a frame synchronizer/TBC (like the original Color TBC or upcoming TBC2, or an external rackmount device) to get 2x unsynchronized external sources into the system

Long answer: A video device can either be generating the sync reference or it can synchronize itself to the sync reference of another video device. Every device which must be synchronous has to point back to only one source for that sync reference.

If you have 1x Cortex generating video, you have a master sync reference.
If you have 1x Cortex + Camera input, you have a master sync reference (now the camera) + one synchronized device (Cortex)
If you have 2x Cortex + Camera input, you have a master sync reference (the camera) + two synchronized devices (Cortex #1 and Cortex #2)

In order to add a second camera to the above setup, it would need to already be synchronous with the first camera. A camera that has a genlock/sync input could do this. But two consumer DVD players could not.

In order to correct timing differences between video sources which don’t have this genlock/sync reference capability, you need a device called a frame synchronizer. This device digitizes the video and stores it into digital memory and then plays it back out in time with the master sync reference. You can often find broadcast TBCs/frame syncs on the secondhand market cheaply, but it may take some digging to find the right one for your setup. Or you could use the LZX Color TBC (or upcoming TBC2) to synchronize the signal and output direct to 1V RGBs.

The dual Cortex scenario favors having an external YPbPr output video device with genlock input because you have two input decoders already. You could then feed one of your Cortex video outputs directly to the genlock input of the receiving device.


OK thanks for helping me work this out. It’s really good to know that there are solutions for this as I’m very keen on exploring this type of mixing.

I ordered a TBC2, luckily October is not too far off - looking forward to taking the TBC2 to feedback land with me :clown_face:

Thanks again your help is much appreciated!!

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Thank YOU for having this dialogue in our new community site space. We’re really hoping this site sticks so that others in the future can follow along and learn with troubleshooting conversations, and that we can build upon a repository of knowledge here.

TBC2 + Dual Cortex is going to be quite powerful! That’s three source inputs, and a fourth if you can find a device with genlock input.


@creatorlars I seem to be having a bit of an issue when trying to get dual cortex’s to sync properly. (see attached photos below) When bringing in my external source via Cortex #1’s input decoder, it looks fine when the decoders 1v output is patched into Cortex #1’s compositor (as seen in the image below) BUT when I plug that same1v output into Cortex #2’s compositor the image has a slight lateral jitter and seems just a bit less sharp. The sync generator shows that everything is locked and it never flashes green or red to indicate it loosing sync, but just has a slight side to side jitter. I am not sure why this is the case?

I have Cortex #1 set up as the “master” and switch on the PCB set to Decoder and Cortex #2 set to Genlock Source. I think that is correct? I don’t know if the “sync to power bus” switches would have any effect on this or not, I have tried those switches in both positions? I have been curious about those switches anyway, if I do not have any video OSC in my system do I even need to be concerned with those? I am not attempting to sync anything to the power bus, any modules that have sync in my system are being chained via RCA sync underneath all the modules.

Try a different video source (DVD players are usually especially stable) and let me know if you see a difference. Can you capture quick clips of the jitter and non/jitter you’re seeing?

I am not with my rack at the moment, but, I tried a couple of different sources first a loop from AndOr1 which is usually stable for me going into Cortex and then using Structure’s composite out (with just a still image of a calibration chart) into Cortex, both had the same symptoms as noted above.

Will try and capture a clip when I get a chance to get back in front of the setup again.

Do you have a video distribution amp? You may need to send sync (identical source) into both Visual Cortex in parallel. Unfortunately Cortex does not have a loop thru jack like the other modules do. Try this experiment if you don’t mind, and let me know what you find out.

Unfortunately, I do not have a video distribution amp, but, just to make sure I am understanding you correctly, are you saying that I should run sync into the “master” cortex’s RCA sync input as well? Instead of terminating at the last module could I just run the RCA sync from the last module in the sync chain back into the “master” Cortex’s RCA sync input? Like a sync feedback loop…? :smile::smiley:
The Cortex’s are #1 and #2 in my sync chain…

Yes, you could do it like that! But then you still need to go in via the frontpanel if you want to use the input decoder of one of the Cortex. I’m not trying to say this is the final solution, more just curious if this solution resolves what you’re seeing.

@creatorlars I have attached one video clip from Cortex #1 and the jittery Cortex #2. I tried to add sync from Cortex #1 RCA output to Cortex #2 input decoder for additional sync help, but, it did nothing to stop the jitter.

Hmm… for some reason it won’t allow me to upload the video I will send it to support via email…

Can you try synchronizing both Cortex to the same independent video source, using a proc-amp or a device with some synchronous outputs? (For example, the composite video and component Luma outs on the back of a DVD player are usually synchronous.)

@creatorlars Ok, so I ran the composite output from my DVD player to the input decoder of the Cortex#1 and the component output into the input decoder of the Cortex#2.

When I played the movie it seemed like there was not any jitter through either Cortex feed.

The weird thing is that when the DVD player stopped and went to the screen saver, it started jittering while the screensaver was still, and then when the screensaver went into a mode in which it was changing exposure/color/etc. the jittering stopped again?

Is it possible that this could be caused by having a locked still image running through the input decoder? When it was jittering before I had a still image from Structure running through it…?


Cool, I’m glad that solved the issue. My suggestion for you is to get an external video distribution amp. The outputs of it should go to both Cortex in parallel, rather than chained behind the modules. The input can be whatever your house sync or genlock source (external video source) is. A component video distro amp is handy so you won’t get any delay between rebuffered luma and PbPr.