13-09-2020, 06:52 AM
I'm pondering on how to do a really effective field sync separator. I'm currently using what is effectively a monostable to ignore H sync pulses. This is sensitive to impulse interference and I can see a fair bit of that on the recordings we were using yesterday. I could see the video dropping down below black level at times plus disurbances below sync tip.
I separate syncs by simple slicing. The threshold is adjustable in software so I might go a bit lower than halfway down. That will reduce some of the spurious syncs.
Traditionally TVs use an integrator of some kind to separate V sync. This will tend to reject unwanted impulses. I could do something similar in digits by starting a counter on the leading edge of sync and then only flag a V sync pulse when it reaches a high enough count. If I know the signal has correct broad pulses I can do the test multiple times in a single V sync.
Unlike in a TV, I also have to distinguish between odd and even fields. I do this fairly crudely by noting whether the first broad pulse occurs halfway through a line or not. I can probably make this more resilient by gathering evidence from multiple V syncs. If I accumulate the result from several V sync pulses then I can set a threshold for believing that my internally generated odd/even sequence is wrong.
I separate syncs by simple slicing. The threshold is adjustable in software so I might go a bit lower than halfway down. That will reduce some of the spurious syncs.
Traditionally TVs use an integrator of some kind to separate V sync. This will tend to reject unwanted impulses. I could do something similar in digits by starting a counter on the leading edge of sync and then only flag a V sync pulse when it reaches a high enough count. If I know the signal has correct broad pulses I can do the test multiple times in a single V sync.
Unlike in a TV, I also have to distinguish between odd and even fields. I do this fairly crudely by noting whether the first broad pulse occurs halfway through a line or not. I can probably make this more resilient by gathering evidence from multiple V syncs. If I accumulate the result from several V sync pulses then I can set a threshold for believing that my internally generated odd/even sequence is wrong.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
