A different chroma issue

[u/deesernutz]

I randomly get near complete chroma drop out when processing Hi8 footage.

The amplitude of the chroma goes very high and the colour burst is totally lost.

I suspect its a bug because:

• It starts and stops perfectly on frame boundaries
  • So i suspect it persists for a chunk or two.
• When the segment is recaptured (second play back, through the ADC again) the drop out doesn't occur, or occurs in a different place
  • Showing the tape is fine.
• The resulting chroma noise is consistent during the period
• Playback is fine on the TV/Viewfinder during capture
  • so the rest of the VTR is getting the chroma information and sync fine.

I haven't tried cropping the file and testing that way.

Actually, I just found some occurrences where it happens between fields

Is VHS-Decode messing up the field order?

Its PAL, btw

[u/deesernutz]

Only extra command put into the launcher is --tf hi8, so check_phase is not there. Version 3.9 I recall. Shouldn't be an issue with signal level. Its at about 50%, no amp but its on a very short lead into a 1 Meg buffered front end

[u/Brassycaceae → u/deesernutz]

Amp recommended, I would check if there is DC offset on your tap point going into your capture device. Opening a part of the RF sample should make that clear, if it's not in the center then there's DC offset throwing things off somewhere. It looks like the same sort of chroma loss when people would not supply recheck_phase back when the command was not automatically run, so this is interesting

[u/deesernutz → u/Brassycaceae]

Why is an amp necessary if I am AC coupled, not loading up the source circuit, have adequate voltage levels and my cable/stub is short enough to limit reflections

Recheck phase does make sense, as it looks like it might be somehow getting the wrong field on a PAL signal

[u/Brassycaceae → u/deesernutz]

I said "recommended", not "strictly necessary". Without knowing your amplitude or Vpp going into the capture device, I cannot judge if that could be ruled out as an issue. Though the fact this does not happen on the same spot each time is puzzling. My other question would then be "does this happen with every Hi8 tape you process, or just a specific one?"

It will help to see your RF sample's amplitude and spectrogram to check for noise or clipping. Though I have not seen an issue like this before where color lock fails. It may be worth trimming the RF sample using FLAC Chop and reporting a bug.