Re: [AV Media Matters] How lossy?

[Stuart Rohre <rohre@ARLUT.UTEXAS.EDU>]

Witfh due attention tof equalization frequency response vs. amplitude, a
scientific recording that had an unbalance of broadband signal, (under
recorded) to a housekeeping superimposed pulse signal was recopied to regain
the data.

In other cases, an over recorded housekeeping pulse timing signal as above,
was attenuated in the copy to not overload the flux levels of the copy.

In other cases, worn heads had altered the normal record equalization, over
favoring the high frequencies.  In copying, we altered the equalization to
restore the proper balance of frequencies.

Another time, it was desired to accomodate very high level shipping acoustic
signals with wide dynamic range.  By altering the record bias we could alter
the recording from a wideband copy to the equivalent of an intermediate copy
to accept this strong signal.  The altered bias drove the recording of the
copy deeper into the magnetized layer.

For some recovery of low level data, we have transferred direct mode tapes
to an FM instrumentation copy.  There are many equalizing tricks of the
trade, just as there are in the music industry recordings.  Often a hit
recording comes out of what the mixing staff have done in the control room.
Some of the earliest recording augmentation started with Les Paul's
recordings of the 50's, and the Beatles studio staff took this to new
heights that made them stars.

This is not something we do and denigrate digital methods, it is just that
with the tools at hand, many good things can be done in both analog and
digital worlds.

In the aerospace scientific instrumentation field there are thousands of
analog tapes that still contain very important or historic data, and some of
these were recorded under very trying conditions, that made special copying
for analysis vital to their use.

Stuart M. Rohre
ARL U. Tx A/D and Recording Lab
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