26-06-2020, 06:42 PM
Hi Francis
Welcome to the forum.
Like Jeffrey I didn't see this post until today either.
Thanks for sharing the results you got from recording 405 lines to VHS and Betamax and the trying to convert to 625 lines with a Hedghog II.
I was afraid that might have been the case. As you have said a timebase corrector before the converter should help.
A frame store in the converter would help but I don't believe it would help enough to give good results.
The majority of the development of the 405 to 625 converter was done on a different board to Hedghog.
On it I had access to a frame store. Using the frame store resulted in the timing errors reducing by what looked like approximately 50%.
The reason I believe that the frame store didn't give a better improvement is because the problem is coming from the video decoders data clock.
The video decoders clock is locked to the incoming videos line sync. When the decoder comes across a mistimed sync the data clock rings like hell while it is trying to lock to it.
The video decoders data clock is used as the write clock for the frame store. When lines that have been wrote to the frame store while the data clock has been ringing are read back they will be shifted left/right and compressed/expanded.
Jeffrey has suggested in another thread of disregarding the decoder clock and implementing another stable clock to run the 405 input. I think that would have the best chance of working. It wouldn't be the easiest thing to implement.
In another thread on this forum I am building a programmable standards converter. It should be able to do most 25/50 Hz standards. If I get it finished it may be able to do some of what you want to do if you cant get your hands on a WC-01.
Frank
Welcome to the forum.
Like Jeffrey I didn't see this post until today either.
Thanks for sharing the results you got from recording 405 lines to VHS and Betamax and the trying to convert to 625 lines with a Hedghog II.
I was afraid that might have been the case. As you have said a timebase corrector before the converter should help.
A frame store in the converter would help but I don't believe it would help enough to give good results.
The majority of the development of the 405 to 625 converter was done on a different board to Hedghog.
On it I had access to a frame store. Using the frame store resulted in the timing errors reducing by what looked like approximately 50%.
The reason I believe that the frame store didn't give a better improvement is because the problem is coming from the video decoders data clock.
The video decoders clock is locked to the incoming videos line sync. When the decoder comes across a mistimed sync the data clock rings like hell while it is trying to lock to it.
The video decoders data clock is used as the write clock for the frame store. When lines that have been wrote to the frame store while the data clock has been ringing are read back they will be shifted left/right and compressed/expanded.
Jeffrey has suggested in another thread of disregarding the decoder clock and implementing another stable clock to run the 405 input. I think that would have the best chance of working. It wouldn't be the easiest thing to implement.
In another thread on this forum I am building a programmable standards converter. It should be able to do most 25/50 Hz standards. If I get it finished it may be able to do some of what you want to do if you cant get your hands on a WC-01.
Frank
