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OPTIMOD-PC
INTRODUCTION
poor way to set the levels of different audio files on a playout system. Absolute
peak levels have nothing to do with loudness, so peak-normalized files are likely to
have widely varying loudness levels depending on the typical peak-to-average ratio
of the audio in the file. Because of over-use of peak limiting in today's CD mastering
(which has the unfortunate side-effect of sucking the life and punch out of music),
the average level of a CD produced in the '80s can be as much as 15 dB lower than
the average level of a CD produced today. When a playout system segues two such
disparate peak-normalized files, this can cause audible loudness inconsistencies in
your broadcast/netcast while OPTIMOD-PC's AGC section corrects the loudness.
OPTIMOD-PC's AGC section uses window-gating technology to minimize the audibil-
ity of such gain riding. Even so, 15 dB of level correction can take several seconds
and is determined by OPTIMOD-PC's AGC release time setting.
It is far better to normalize levels in a playout system by making the average levels
of all elements identical, which means that they would all peak at the same level
when observed with a VU meter. This allows OPTIMOD-PC's AGC to work as unob-
trusively as possible. Moreover, if your system includes locally originated speech ma-
terial, using a microphone processor (like the dbx 286A) will help smooth the transi-
tion between live and recorded program segments.
The OPTIMOD-PC Digital Audio Processor
OPTIMOD-PC is a PCI card that fits in an IBM-compatible PC and processes one stereo
audio stream or two mono audio streams. It is equally suitable for netcasts and digi-
tal radio or television broadcasting. With its supplied WAVE drivers, it looks like a
standard sound card to your native applications, like the Orban's Opticodec-PC®
MPEG4 AAC/aacPlusV2 streaming encoder. However, unlike a sound card, OPTIMOD-
PC packs hundreds of MIPS of built-in DSP processing power, allowing it to apply
broadcast-quality audio processing to your netcast or digital broadcast without
loading down your computer's CPU with DSP tasks.
OPTIMOD-PC is useful for users with multiple streams because you can load one
computer (which may be connected to a PCI expansion chassis) with as many
OPTIMOD-PC cards as you have free PCI slots, each card handling one stereo pro-
gram. Each card has two AES3 or SPDIF digital inputs and one high-quality analog
input, all of which can be mixed—built-in sample rate converters allow digital
sources to be asynchronous. The card also offers an AES3 output and an analog
monitor output. Therefore, you can route audio through the computer's PCI bus or
entirely independently of the computer—the choice is yours, and will depend on
your application. For example, DAB multiplexes can use multiple OPTIMOD-PC cards
to save cost and space by comparison to stand-alone processors. (The multiplexes
would use OPTIMOD-PC's AES3 inputs and outputs, and could exploit OPTIMOD-PC's
ability to genlock its output sample rate to the sample rate applied to either AES3
input.) OPTIMOD-PC (including the I/O mixer) is also fully remote controllable over a
network.
The rest of Chapter 1 explains how OPTIMOD-PC fits into the DAB and DTV broad-
cast facilities, and how it can be used for netcasting. Chapter 2 explains how to in-
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