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Timing issues

Dear Mr. Robin:

I work for the regional TV station in Yugoslavia. We have been almost completely analog for the last 12 years and have no real experience in digital equipment. Now we have some secondhand digital equipment, and we are trying to combine it with what we already have. What we have now is a Philips production switcher with component inputs for cameras, and other inputs are SDI. The trouble is that we have only two SDI sources: DVCPRO and a frame synchronizer. So we're going to put an analog switcher before that synchronizer in order to have more sources available. At the end we have DigiMix as a keyer.

What we want to know is the method of measuring all these paths and doing timing, taking into consideration that all we have is some old Tektronix analog waveforms and vectorscopes.
Kresimir Vlahek

Michael Robin responds:

Dear Mr. Vlahek:

In response to your note, I have several suggestions. First, provide all analog and digital equipment with a common PAL color-burst reference signal.

Second, time and phase all analog sources feeding the analog production switcher to your normal PAL tolerances and check the results by switching from one source to another while monitoring the analog PAL output with a PAL vectorscope and a waveform monitor referenced to the central PAL color-burst reference.

Following these steps should be sufficient. Normally, digital production switchers with SDI inputs feature a synchronizer at every input with a tolerance window of +/- 0.5H. I am not familiar with the Philips production switcher you are using, but in all likelihood, it operates in a manner similar to other products I am familiar with.

Insofar as the analog-component camera inputs of the Philips digital production switcher are concerned, I am assuming that each set of component analog signals is digitized for further digital processing, so it would seem normal that it uses the same synchronizer circuitry as the SDI inputs. If this is the case, steps one and two should suffice.

Normally, you would want to monitor the SDI output of the switcher. To this effect, I would suggest a digital waveform monitor of the Tektronix WFM601 family, whose decoded analog GBR or Y, B-Y, R-Y outputs feed a component analog color monitor. That version would allow you to verify the integrity of the SDI signal, as well as that the resulting analog PAL signal is valid and legal.

I hope these suggestions are of help.
Michael Robin

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