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Posted by nobody special on 03/24/06 05:32
Back in the 90's we saw this problem on a number of VHS and SVHS
camcorders, and one of the hacks around it was to deliberately feed
some very high or very low-frequency noise into the circuit, which
responds no so much to frequency as volume. It would only take a small
amount of volume for this frequency to trip the AGC to a certain level
where it would just sit, unless the regular audio suddenly became
really loud. This would take out the constant hunting or pumping up and
down for level. The theory, which worked about half the time, as I
recall, was that in post you could just notch or low-pass or high-pass
the selected "pilot tone" out because it was far out of the regular
range of sound the human ear could detect. I also used some
camcorders that had had an "AGC-ectomy" performed inside them by some
local tinker; these had mixed results and were not too dependable or
consistent.
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