What cause phase shift of color signal in NTSC?

infoeater · 20th July 2013, 14:02

As I understand there is colorburst signal before each line in NTSC. So chroma QAM signal is resynced many times per field. If so how it's possible that color shift occurs. How it is possible that color shift is equal in many thousands of consecutive whole fields (so manual tint compensation is possible)?

raffriff42 · 20th July 2013, 16:21

One, operator error or equipment miscalibration. Color burst and sync are regenerated at many points in the signal chain and it's possible to get the phase wrong - especially when mixing signals (delay errors) or playing back a consumer video tape.

Two, differential phase. Burst is at zero IRE, visible chroma signal goes from -20 to +120 IRE, IIRC. Phase distortion can creep in.

Three, burst phase detection itself can be in error. It's a complex bit of circuitry.

Four...?

Ghitulescu · 21st July 2013, 15:07

Quote:

Originally Posted by raffriff42

Four...?

Never the same color.

infoeater · 21st July 2013, 20:25

Thank you very much raffriff42. Now I understand. Most articles described NTSC color distortion as coming magically from "transmission" during bad weather.

20th July 2013, 14:02	#1 \| Link
infoeater Registered User Join Date: May 2007 Posts: 53	What cause phase shift of color signal in NTSC? As I understand there is colorburst signal before each line in NTSC. So chroma QAM signal is resynced many times per field. If so how it's possible that color shift occurs. How it is possible that color shift is equal in many thousands of consecutive whole fields (so manual tint compensation is possible)? Last edited by infoeater; 20th July 2013 at 14:19.

20th July 2013, 16:21	#2 \| Link
raffriff42 Retried Guesser Join Date: Jun 2012 Posts: 1,373	One, operator error or equipment miscalibration. Color burst and sync are regenerated at many points in the signal chain and it's possible to get the phase wrong - especially when mixing signals (delay errors) or playing back a consumer video tape. Two, differential phase. Burst is at zero IRE, visible chroma signal goes from -20 to +120 IRE, IIRC. Phase distortion can creep in. Three, burst phase detection itself can be in error. It's a complex bit of circuitry. Four...? Last edited by raffriff42; 20th July 2013 at 16:28.

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21st July 2013, 20:25	#4 \| Link
infoeater Registered User Join Date: May 2007 Posts: 53	Thank you very much raffriff42. Now I understand. Most articles described NTSC color distortion as coming magically from "transmission" during bad weather.