Inovonics DAVID IV 719 N, Инструкция по установке и эксплуатации

Страница: 48 / 61

— 44 —
With
ITU
selected, the PIPP* limiter is defeated in favor of more
conservative symmetrical peak control. Secondly, the
Limiter
Drive and
Limiter Density (dB):
sliders are re-scaled for less-
aggressive overall processing. The
Limiter Density (dB):
slider
becomes a
dBr BS.412-9 (dBr):
slider.
The
dBr BS.412-9 (dBr):
slider is recalibrated to the multiplex
r.m.s. “0dBr” value cited in the ITU Recommendation. Neverthe-
less, it may be set at any value between –1dBr and +5dBr, ac-
commodating any ‘fudge factor’ that might be permitted by the
regulating authority in the station’s location.
In operation, the DAVID IV continues to utilize the native algo-
rithm of the
Limiter Density (dB):
slider to anticipate a certain
amount of average-level modulation control based on audio
program dynamics. This approximation works in concert with
feedback of the r.m.s. value of the actual multiplex signal to ar-
rive at a final and accurate correction factor.
Other ITU
Processing
Implications
The
ITU
mode will hold r.m.s carrier modulation to the pre-
scribed limit, but processing ahead of the peak limiter section
will have a second-order effect on how effective this utility will
be in complying with both the letter and the law of the Recom-
mendation .
One caveat of the ITU Recommendation is that audio processing
used to satisfy the requirement must not create audible side-
effects (i.e.: ‘breathing,’ ‘pumping’ and obvious level shifts).
The user must thus exercise conservative judgment and avoid
overuse of Multipressor and other ‘sound-enhancement’ fea-
tures when the
ITU
mode is active.
ADAPTIVE PRE-EMPHASIS
FM Pre- and
De-Emphasis
FM broadcasting makes use of audio pre-emphasis in transmis-
sion and complementary de-emphasis in the receiver. This
practice requires special consideration with respect to program
peak control.
FM pre- and de-emphasis characteristics were established in the
1940s. These were far simpler times in radio programming,
long before the term ‘competitive loudness’ was on the lips of
Program Directors. Broadcast practices and recording tech-
niques from that era did not anticipate today’s sizzling, high-
energy, closely-mic’d and heavily-EQ’d music trends.
Today’s program material severely taxes the ability of the FM
transmission channel to pass content in a ‘transparent’ manner.
High frequency energy must be controlled independently of the
broadband levels, a necessity that can make music sound as
‘dull’ by today’s standards as, in fact, any recorded music might
have sounded to many of us if we were transported back to
those halcyon days.