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noise in DigiBeta transfers



July2 Steve Gladstone wrote:

In the transfer room, the image looked pretty decent. However I thought it was
a little noisey. I was informed that the Noise reducers were on full. Since I
had been given Bad Directions I missed the first 15 minutes of the transfer,
when the crucial Noise Reduction was applied. This was before I caught the
whole warning of overusing Noise Reducers.
As I said the image in the monitor in the Transfer room looked very clean.
However in subsequent Edits, and Dubs from the Digi beta the transfer was
recorded on, there is What looks like Video noise? White dots, very small and
in a fixed pattern seemingly strobing. I have not been able to see the
original Digi-beta of the transfer, but We did not see this in the Telecine
Suite, only after. It is on every copy, and dub, and edited peice made from
the Digi-beta.
------------------------

We have seen this sort of thing several times when going to DBeta from a
Diamond, particularly on grainy film, enough that we now routinely
recommend transfer to D1. Sony has acknowledged one aspect of the problem
in Broadcast products Technical bulletin 1997-074. What seems to be
happening is that the extended high frequency response of modern telcines
can pass "out of band" signals to the VTR which can in turn generate
garbage further downstream which appears as noise, particularly when the
tape is viewed via the "normal" NTSC analog output. Sony admits that this
output of the Dbeta machines is only intended to be a monitoring output, as
the built-in encoder is not of exceedingly good quality. They don't spend a
lot of time and trouble putting sophisticated filtering into the machine.

I have noticed significantly cleaner pictures coming from both the digital
and component analog outputs. When encoded by a high end encoder with good
filtering (such as Faroudja or Miranda units) the NTSC signal is much
improved. In at least one case I had to supply finished spots to the dub
house via a D2 dubbing master digitally encoded by my Miranda ENC100D, in
order to overcome excessive noise on the air dubs.

Unfortunately nearly everyone making 1" and D2 air dubs and VHS or
Laserdisc copies use the DBeta machine's built in encoder. Sony's answer is
to modify all playback VTRs to make the internal encoder less susceptible
to these out of band signals. Obviously not everyone is going to do this,
so the film transfers have to be filtered to be free of this effect in the
first place. The compression engine within Dbeta is also upset by out of
band signals and high frequency noise which usually is otherwise masked by
normal (and possibly desireable) filmgrain and therefore not apparent on
the Telecine suite monitor. Further signal processing encountered by the
video during editing may or may not contribute to the overall degradation
of signal purity. Once the noise is recorded in, however, it cannot be
cleanly removed without incurring mor of those pesky "noise reducer"
artifacts that everyone is yelling about on this newsgroup.

So we have to filter the telecine output before it hits the VTR. This can
be accomplished handily by the judicious application of some noise
reduction, even when you don't think it is necessary upon viewing the
telecine suite monitor. The only way to know is to actually monitor the VTR
confidence output, preferably both in digital component and in (built-in)
NTSC analog, during the transfer. But at this stage it is not visible noise
we are concerned with, so perhaps a noise reduction unit does not offer the
right kind of filtering. I have found that in many cases simply going
component analog into the Dbeta machine rather than using the telecine's
component digital interface, the problem is minimized. I am waiting for an
opportunity to try other video filters/processors from several
manufacturers which may be able to deal with this particular issue without
introducing softness or other artifacts. It is not even completely clear
whether transfers originally done to D1 or D5 but edit mastered to DBeta
remain free of these effects.

I wish I had access to the original film now from a couple of those problem
jobs we had to find workarounds for.

Terry Lockhart
Chief Engineer
Finish Editorial
162 Columbus Ave.
Boston, Ma 02116-5222

Beeper 800 973 5142
voice 617 292 0082
fax   617 292 0083
terry.lockhart at finishedit.com



---
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