Linear Acoustic has been invited to address the Society of Broadcast
Engineers on ways to control and maintain consistent audio levels during
multichannel HDTV transmission. Company president Tim Carroll will speak to the
Sacramento SBE Chapter 43 on January 24, 2006, and San Francisco SBE Chapter
40 on January 25; both are noontime lunch meetings.
“Through the use of AC-3 audio data-compression technology—better known as
Dolby Digital—DTV has the capability of delivering pristine-quality
digital audio,” Carroll says, “with a potential dynamic range exceeding
100 dB on each of its 5.1 channels, equaling or surpassing the performance
of a high-quality movie theater. While such a specification looks good on
paper and is referred to as ‘What Hollywood has always asked for,’ it is
unclear whether this dynamic range is appropriate for the typical television
viewer.
“Importantly,” Carroll continues, “the AC-3 system makes a basic assumption
that audio dynamic range and program loudness are separable and can be
controlled independently. This is a dramatic departure from the actions of
legacy broadcast dynamic range processors installed at so many broadcast
stations and networks. While there are some controls built into the
so-called metadata portion of AC-3 to help tailor the audio for appropriate
presentation to each listener, these parameters must be set correctly on
each program for the system to function effectively. This means that
current audio producers must not only take care to make good-quality audio,
but also take the time to author proper audio metadata. Assuming this takes
place, are there any guarantees that the metadata will make it intact all
the way to the point of transmission? What if it fails or is maliciously set
incorrectly?”
Carroll considers that the question of controlling dynamic range boils down
to a single question: Is it all working? “In an effort to answer this
question,” Carrols says, “my presentations to the SBE chapter meetings will
explore some real-world scenarios and their measured results. I will present
actual examples of successes and failures, and the root cause of each will
be described, along with technical details of several add-on solutions
designed to help broadcasters and consumers. And I will also take a few
minutes to explore surround for digital radio and discuss some of the
technical challenges emerging in this new market.”
Information on the Sacramento SBE Chapter 43 meeting can be found at
www.sbe43.org and information on the San Francisco SBE Chapter 40 meeting can be found
at www.lns.com/sbe.
