Inovonics 235, Инструкция по эксплуатации и техническому обслуживанию

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Plus AGC readings (+5, +10) indicate that the input signal
is below the optimum level and that the circuit is slowly
bringing the gain up. Minus readings (there are no such
things as negative dBs, at least not in our space/time
continuum) show that the input signal is too “hot” and that
the level is being reduced to compensate.
COMPRESSION The definition of compression generally acknowledges a
reduction in the average dynamic range of a speech or music
program signal. Program level is frequently (and sometimes
erroneously) expressed in r.m.s. terms and is integrated over
a period of a hundred milliseconds or more. A compression
ratio may be expressed or implied, which might be on the
order of 2:1 or 4:1, indicating a fractional output level
change for a given input level variation.
The Model 235 compresses program dynamics in three
frequency bands. These are labeled LOW, MID and HIGH . In
the interest of maximizing perceived loudness, the
compression ratio in each of these three bands is made
uncommonly steep for a compressor, 20:1 or greater. Thus
the circuit acts more like a 3-band limiter than a traditional
compressor. Attack time within each band is quite rapid;
release, on the other hand, is variable and a function of the
PROGRAM DENSITY setting, which is explained in more
detail under the next heading. The three COMPRESSION
displays show dBs of gain reduction for each band.
PROGRAM
DENSITY
Two up/down buttons allow the operator to choose eight
relative degrees of density control. These are indicated on
the adjacent LED bar display.
Set at
(MIN) , the 3-band compressor has a slow release to
what we call a platform value. The platform is established
by an average of the gain reduction in all three frequency
bands. This platform causes the circuit to perform more like
a single-band compressor, and spectral density of the
processed program audio is only marginally effected.
As
PROGRAM DENSITY is increased toward (MAX) , the
platform and the “blending” of the bands is reduced so that
the full multiband advantage may be realized. Compressor
release timing is progressively shortened as well, and this
imparts a “busy” character to the program to further
increase perceived loudness.
EQUALIZATION In addition to NRSC (or alternative) fixed pre-emphasis, the
235 provides a range of control over both high- and low-
frequency program equalization.
The effect of the equalizers is shown in Figures 2 and 3 on
Page 5. The LOW FREQ. and HIGH FREQ. buttons cycle the
EQUALIZATION settings through the five choices for each