5) Conclusion
-
Although the DVA Profession Fidelity Analyzer can be used to verify all kinds of signal chains that end in the digital domain, our personal focus was on testing video A/D converter hardware.
-
We were surprised to see what video A/D converters actually do on a timing level:
Not all detected effects can be interpreted as errors or malfunctions. Adapting unclocked signal to a clocked environment demands changes in the succession of fields. But it is interesting to see in which ways the tested converters act differently in those cases.
-
We were even more surprised that it seems that no one ever considered verifying the timing-quality of A/D converters. If any tests were done, they are usually focused on image quality.
Tests done with the same source tapes using different A/D converters over the same signal chain showed different ways of handling the same timing issues. The effects of these issues affect the output video in different degrees. Especially because converting a video recording from the analogue to the digital world requires some changes in the signal, the knowledge which converter is matching the original most accurately, is worth knowing.
-
Still, we haven’t been able to find a converter that we are comfortable with using it to produce a digital copy, suitable as new “original” for long-term video archiving.
-
DVA Fidelity shows a high potential for optional expandability in the future.
The created test scenario with the generated testfile being analyzed by a script which knows, what exact kind of field to be expected next, offers a wide range of possible behavior to be additionally tested:
- measuring exact values and behavior of sync shifts between audio and picture
- changing color values during processing chains
- measuring format changes (e.g. true 16:9)
- detecting cropping effects in the chain
-
As verifying quality and behavior of signal chains and/or equipment is often only a onetime necessity when new equipment is added or parts of an existing video signal chain are changed, it might often not pay off for some institutions to have their video technicians gain in-depth knowhow about DVA Fidelity test scenarios themselves. Therefore it would make sense to offer Fidelity-Testing as a service.