Inovonics DAVID IV 719 N, Инструкция по установке и эксплуатации

Страница: 47 / 61

— 43 —
A proper setting of the
Limiter Density (dB):
control is deter-
mined entirely by subjective evaluation of the on-air sound.
Density is one very important quality of the station’s signature
sound, and no other control has a greater effect over perceived
loudness. The factory default value is a setting of 0dB, the cen-
ter of the control range. There is no setting considered a wrong
one, but the range extremes will probably be useful only in spe-
cial situations. Use your ears and consider the long-term lis-
tener fatigue effects of very dense programming.
MULTIPLEX POWER CONTROL (BS.412-9)
The ITU
‘Recom-
mendation’
In 1998, the International Telecommunication Union (ITU), a
key European standards organization, published their Recom-
mendation ITU-R BS.412-9 , the culmination of several years’
work to study and mitigate interference between broadcast sta-
tions on the crowded European VHF-FM band.
Channel spacing, transmitter power and other assigned consid-
erations were major factors in this study, but insofar as audio
processing is concerned, the short version is that the ITU found
direct correlation between FM carrier modulation and audible
interference between stations on adjacent frequencies. What’s
more, it further found that modulation density was in large part
responsible for this interference. In other words, not necessari-
ly the absolute peak deviation of the carrier but the r.m.s. pow-
er of the modulating program signal integrated over a specified
period of time.
The ITU
Recommendation specifies the r.m.s. power of the
composite-multiplex signal (including the stereo pilot and any
audio (SCA) or data subcarriers), as measured and integrated in
a ‘floating’ 1-minute measurement window. It states that this
value should not exceed the r.m.s. power of a single-tone sine
wave modulated with a peak deviation of ±19kHz.
Now, ±19kHz is just about 12dB below the ±75kHz peak devia-
tion limit. This implies an average-to-peak ratio of the program
signal that, by contemporary broadcasting standards, gives a
rather pathetic showing… certainly not the in-your-face, highly-
compressed dynamics that Program Directors have come to
know and love(!) since the mid-1960s!
The ITU
Recommendation has been mandatory in Germany,
Austria and Switzerland since 2004, but with some latitude.
Germany adheres to the letter of the Recommendation , “0dBr”
they call it. But Austria and Switzerland are able to exceed that
point by 3dB. In other words, their r.m.s. modulation is permit-
ted to go to “+3dBr.”
The DAVID IV provides compliance to the ITU standard by re-
defining the peak-limiting processing function when the
ITU
limiting mode is selected.