Maintaining Audio Quality in the Broadcast Facility 2011 - Orban

in the Broadcast/Netcast Facility 51
Conventional AM, FM, or TV audio processors that employ pre-emphasis/deemphasis
and/or clipping peak limiters do not work well with perceptual audio coders
such as AAC/HE-AACv1/v2. The pre-emphasis/de-emphasis limiting in these processors
unnecessarily limits high frequency headroom. Further, their clipping limiters
create high frequency components—distortion—that the perceptual audio coders
would otherwise not encode.
In addition, several audio processing manufacturers offer pre-processing claimed to
minimize codec artifacts at low bit rates. Orban’s technology is called PreCode.
This manipulates several aspects of the audio to minimize artifacts caused by low
bitrate codecs, ensuring consistent loudness and texture from one source to the
next. PreCode includes special audio band detection algorithms that are energy and
spectrum aware. This can improve codec performance on some codecs by reducing
audio processing induced codec artifacts, even with program material that has been
preprocessed by other processing than Optimod.
Summary
Maintaining a high level of broadcast/netcast audio quality is a very difficult task,
requiring constant dedication and a continuing cooperation between the programming,
engineering, and computer IT departments.
With the constantly increasing quality of home and mobile receivers and stereo
gear, the broadcast audience more and more easily perceives the results of such
dedication and cooperation. One suspects that in the future, FM, DAR, and netcasts
will have to deliver ever-increasing quality to compete successfully with the many
other program sources vying for audience attention, including CD’s, DVD’s, Blu-ray
disks, digital audio, subscription television, direct satellite broadcast, DTV, streaming
programming on the Internet, high resolution downloads and who knows how
many others!
The human ear is astonishingly sensitive; perceptive people are often amazed when
they detect rather subtle improvements to the broadcast audio chain while listening
to an inexpensive car radio. Conversely, the FM broadcast/reception system can exaggerate
flaws in audio quality. Audio processors (even OPTIMOD) are especially
prone to exaggerating such flaws.
In this discussion, we have tried to touch upon the basic issues and techniques underlying
audio quality in radio operations, and to provide useful information for
evaluating the cost-effectiveness of equipment or techniques that are proposed to
improve audio quality. In particular, we concluded that today’s high-quality IC
opamps are ideally suited for use as amplification elements in broadcast, and that
compromises in digital standards, computer sound cards, disk playback, and tape
quality are all likely to be audible on the air. The all-digital signal path is probably
the single most important quality improvement that a station can make, but the installing
engineer must be aware of issues such as lossy compression (particularly
when cascaded), word length, sample rate, headroom, jitter, and dither, and
0dBFS+-induced clipping.