Watchpax sync

[Playground]

Hi

 

I am looking at watchpax as a signage solution and exhibition solution.

I intend to use it on large LED walls that exceed the normal 1920 wide pixel space 

I am curious if watchpax can maintain sync over its outputs rather than a server with s400 card

any thoughts welcome

Cheers

Ben

 

[Alex Ramos]

Yes is sync enough for most LED screens, but its not frame sync.

Only once I really needed the S400 for an LED screen and that was a time I need to run some horizontal text across the all screen.

 

To be on the safe side I would use the S400 anyway. 

[jfk]

Software synch is frame accurate, but not scan accurate. (WATCHPAX is software synch only)

Hardware assisted synch (s400) is scan accurate.

 

Generally, when connecting directly to projectors or mullioned displays,

software synch is adequate.

 

when connecting to processors (vision mixers like Spyder, BlendPro, etc)

or wall systems where there is 0 pixel seperation between adjacent outputs,

hardware synch is required to achieve transparent results.

 

 

 

 

[RBeddig]

We recently tested the WATCHPAX 4 with 4 LED processors on one LED (4x 1080p60) and did not see any tearing or other sync related issues on the border between the four outputs/processors.

 

I would call the outputs of a WATCHPAX 4 genlocked indeed.

 

If you need more than 4 outputs you should definitely go for servers with S400 or Nvidea syncboards if you prefer Nvidea.

[reod]

So presumably you would indeed experience sync loss over time if you were using 2 Watchpax4's to achieve 8 displays for instance?

[jfk]

So presumably you would indeed experience sync loss over time if you were using 2 Watchpax4's to achieve 8 displays for instance?

 

They will never lose frame synch.

They will intermittently lose scan synch.

[mindopera]

Can you explain the difference between scan sync and frame sync?

And does having frame sync matter if there is no scan sync?

[Miro]

Hi, frame sync happens over network so that all devices are rendering the same frame at the same time. Scan sync or genlock means that the scan out of the ports of the GPU are synchronized. A synchronization card can also achieve genlock across several GPUs/servers.

 

If two GPUs are not connected using a synchronization card the following will happen:

1. Even if booth GPUs are rendering at 60 Hz they will not scan out/transmit the signal at the same time and will be out of phase. They will render the correct frame (frame sync) but there might be a slight offset between the display devices (mostly not noticeable)
2. The timing devices in each GPU are not synchronized so the perception of time is a bit different. Both of the GPUs will render at 60 Hz relative their internal clock, but relative to the production computer (cluster master) clock they might actually render at 59.9999 and 60.00001 Hz.. The slower GPU will need to drop a frame after some time while the faster GPU will need to duplicate a frame after a while.

If using synchronization cards but having a bad network might result in bad frame sync.. Even if all GPUs will keep the exact 60 Hz timing and scan out the signals to the displays at the same time, the rendered content might be out of sync. The clock time stamp from the master will be multicasted using UDP. On a normal setup this time stamp can have an offset of +- 0.5 milliseconds (in 60 Hz each frame time is 16.666667 ms) between servers. In extremely rare cases this could result in that a video frame would be scheduled into the incorrect display frame causing a very brief mismatch between what is shown on the outputs.

 

On Nvidia and AMD GPUs (pro and gamer versions) all outputs are automatically genlocked if they output a signal with the same timing (same resolution and refresh rate).

 

Hope this make some sense..

 

//Miro

[mindopera]

That's a great explanation Miro. Thank you