Reply To: HDMI-to-VGA adapter

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#23230
James-F
Participant

I think I know why the wobbles appear.

I short, the output from the analog-to-digital conversion from the OSSC or RetroTink2x is not perfect since it was sampled from an analog signal and not generated digitally from a PC GPU for example.

Every time there is an analog to digital sampling stage there is phase and clock adjustments, basically, how often and where to sample.
When the OSSC samples the RGB input it has H.samplerate for “clock” and Phase that the user can change.
When sampling low analog horizontal resolution like 320 or 256 with high H.samplerate the image will be sharper and more stable.
Sampling any resolution with exact sampling rate for that resolution is what an LCD monitor with VGA input does, or the OSSC in Optimized mode.

When the HDMI-to-VGA dongle converts the digital signal to analog it expects perfect digital signal but because this signal is a sampled signal by the RetroTink2x it is far from perfect and already has phase and clock misalignments.
Therefor the VGA output from this dongle already has these pre-sampled imperfections on the output.

When you input this VGA signal into the OSSC or a VGA monitor, it is samples AGAIN and converter to digital.
In THIS stage you get the wobbles if the clock and phase is not perfectly set (optimized mode) by the OSSC or your LCD VGA input.
To mitigate the wobbles when sampling the VGA input on the OSSC ALWAYS use optimized mode and adjust H.samplerate (clock), till the wobbles disappear.

Use the Checkerboard pattern in the 240p suite to adjust the H.samplerate when adjusting Optimized mode, or lets the LCD VGA-input monitor automatically adjust the clock+phase with this Checkerboard pattern on screen if you are using the VGA input on an LCD screen.

Using this method I was able to reduce the wobbles to minimum so they are practically non visible.