Orban OPTIMOD 6200, Руководство по эксплуатации

Страница: 35 / 195

OPTIMOD INTRODUCTION
1-17
•
The second is Line-Mode Dynamic Range Control, which allows the receiver to per-
form a wideband compression function if the listener chooses.
•
The third is RF-mode Dynamic Range Control, which applies heavier processing.
The obvious question that arises is how these signals are to be generated in a real-world
operational facility. And, indeed, in which situations they should be generated.
We should remember that the marketing landscape is littered with “features” that seemed
to be a good idea at the time, but which proved to be of little or no interest to consumers.
Digital technology has vastly decreased the cost of adding new features to consumer
electronics, and many consumer manufacturers have responded with a blizzard of fea-
tures that are confusing, hard-to-understand, or just plain useless.
For example, CDs have always offered the ability to deliver auxiliary data. According to
the original CD hype, you would see the lyrics of the songs scroll by as you played them.
In addition, you would see still pictures of the band members by connecting your CD
player to your television set. Where are these features now? The answer, of course, is
that the public did not find them compelling enough to justify the additional production
expense to add them to the CD data stream, or to justify the increase in manufacturing
cost necessary to add the video outputs or the LCD screens to the CD players.
Another example is the SAP channel in BTSC stereo television. Very few viewers un-
derstand it, yet a number of them manage to turn it on by accident. Then they can’t un-
derstand why the sound becomes low-fidelity mono, and why everyone is suddenly
speaking Spanish! Consequently, many consumer manufacturers buried the SAP control
very deep in the menu structure of receivers or VCRs to prevent this confusion from oc-
curring in the future.
Concerning the AC3 metadata, we believe that only a small minority of viewers will ever
understand the concept of dynamic range control. Dolby Laboratories wisely specified
that dynamic range compression would be the receiver default, because they realized that
most consumers would never want full dynamic range audio.
Experience has shown that a vast majority of viewers are not interested in wide dynamic
range. Instead, they want two things. First, dialog should be comfortably intelligible, and
second, commercials should not be irritatingly loud by comparison to program material.
Home theater owners may want the opportunity to watch feature films while hearing a
wide dynamic range signal. However, even these viewers usually consume television in
a much more passive way when viewing garden-variety programs. If television is to be
an acceptable part of the domestic environment, the sound cannot overwhelm household
members not interested in viewing (not to mention neighbors, particularly in multi-
family dwellings). For a variety of reasons, the dynamic range of sound essential to the
intelligibility of the program should not exceed 15dB in a domestic listening environ-
ment. Underscoring and ambient sound effects will, of course, be lower than this.
The issue of loud commercials is particularly important — the FCC has been concerned
with loud commercials ever since the mid 1960’s, and has twice actively investigated the