Maintaining Audio Quality in the Broadcast Facility 2011 - Orban

Maintaining Audio Quality
in the Broadcast Facility
By Robert Orban and Greg Ogonowski, Orban
Authors’ Note
In 1999, we combined and revised two previous Orban publications on maintaining
audio quality in the FM and AM plants and have since revised the resulting publication
several times. In 2011, considerations for both AM and FM are essentially identical
except at the transmitter because, with modern equipment, there is seldom
reason to relax studio quality in AM plants. The text emphasizes FM, HD Radio, and
netcasting practice; differences applicable to AM have been edited into the main
text.
Introduction
Audio processors change certain characteristics of the original program material in
the quest for positive benefits such as increased loudness, improved consistency, and
absolute peak control to prevent distortion in the following signal path and/or to
comply with government regulations.
The art of audio processing is based on the idea that such benefits can be achieved
while giving the listener the illusion that nothing has been changed. Successful audio
processing performs the desired electrical modifications while presenting a result
to the listener that, subjectively, sounds natural and realistic. This sounds impossible,
but it is not.
Audio processing provides a few benefits that are often unappreciated by the radio
or television listener. For example, the reduction of dynamic range caused by processing
makes listening in noisy environments (particularly the car) much less difficult.
In music having a wide dynamic range, soft passages are often lost completely in the
presence of background noise. Few listeners listen in a perfectly quiet environment.
If the volume is turned up, subsequent louder passages can be uncomfortably loud.
In the automobile, dynamic range cannot exceed 20 dB without causing these problems.
Competent audio processing can reduce the dynamic range of the program
without introducing objectionable side effects.
Further, broadcast program material typically comes from a rapidly changing variety
of sources, most of which were produced with no regard for the spectral balances of
others. Multiband limiting, when used properly, can automatically make the segues
between sources much more consistent. Multiband limiting and consistency are vital
to the station that wants to develop a characteristic audio signature and strong
positive personality, just as feature films are produced to maintain a consistent look.
Ultimately, it is all about the listener experience.
Good broadcast operators are hard to find, making artful automatic gain control
essential for the correction of errors caused by distractions or lack of skill. Also, the
regulatory authorities in most countries have little tolerance for excessive modula-
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