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The role of an on-air processor is two-fold. From a functional standpoint, the processor provides the necessary limiting and pre-emphasis to comply with FCC modulation requirements. This important step is often an afterthought today, and subsequently the operational aspects that a processor can provide to a station in creating a sonic identity are given prime attention.
The functional characteristics, for the most part, are easy to address. If nothing else, a brick-wall limiter can ensure that a station does not overmodulate. It may not be the best sounding approach, but it works.
The operational function has become an art of its own. For some, the ability to reduce an audio signal's dynamic range to a few decibels while maintaining the perception of an open, airy sound is the holy grail of audio processing. This pursuit of the ultimate in heavy processing that sounds unprocessed has led to great advances in audio processing methods.
When analog processors were the only choice, engineers would experiment with various aspects of a device to push its operation to the maximum limit of its ability. Changing capacitor and resistor values to vary time constants were the norm. When multiband processing became popular, many engineers formed their own secret recipes to change crossovers and other parameters.
Now that digitally controlled processors have become the leading standard, there is no need to open a device and manipulate the components. Most processors provide full access to every parameter within. With this level of control there is no reason a user should not be able to find that perfect sound by navigating a menu. The added advantage is not needing a box of precision resistors or a soldering iron.
Digital control also offers repeatability. Settings can be stored and recalled at will. Favorite settings can be shared or loaded into other processors at sister stations. Many processors include daypart scheduling, so the presets can change as needed.
The state of technology in audio processing is as high as it has ever been. Whether your need is aggressive compression or an open, natural sound, finding the right settings should be easy.
A sample of available on-air audio processors
This 2RU digital processor combines a straightforward design and
simple operation with a high degree of control. Despite the use of DSP,
the unit introduces less than 10ms of latency to the audio signal and
boots in a matter of seconds. The front panel controls do not use a
menu structure, but instead rely on front-panel buttons and a series of
LED bargraph meters to indicate status and levels. Twelve factory
presets can be recalled and modified through the front panel or through
the RS-232 interface. Connections include analog and digital audio I/O
and a BNC composite output.
Model 2020 MkIII
This is the third generation of this audio processor. Housed in a
2RU chassis, the 2020 does not use multiband clipping or composite
clipping. The digitally controlled analog processor maintains an analog
path throughout the system. A digital input and output interface is
available with an adjustable sampling rate of 32kHz to 48kHz and 20-bit
resolution. 75µs and 50µs pre-emphasis settings are
available. Analog audio I/O and optional digital audio I/O are
available, as well as a BNC composite output. Adjustments are made
through the front panel menu with multiple LED bargraph meters to
Created in a partnership with Neural Audio, this 1RU processor
addresses the needs of processing audio for data-reduced delivery, such
as IBOC and Internet radio, where traditional compression and clipping
methods can introduce unwanted artifacts into the encoded audio. The
modular design allows users to select the necessary processing power
for each application. These modules include spectral image management,
spectral image mapping, loudness management, peak management, noise
reduction, hum removal, low-frequency extension and watermarking. The
spectral image mapping module has the ability to mimic processing
settings from existing sources.
The Optimod-FM 8300 is a mid-priced processor providing many of the
features of the company's 8400. Adjustments can be made with a one-knob
adjustment to customize any factory preset, or with full control to
completely customize the parameters. Experienced users can also use
advanced control. It features a stereo enhancer, a two-band AGC,
selectable two-band or five-band compression and limiting, a look-ahead
limiter and a stereo generator. It includes stereo analog and digital
I/O and can be controlled through a GPI interface, RS-232, Ethernet or
through the external software. Settings can be saved and uploaded and
Featuring 96kHz processing and advanced DSP algorithms to eliminate
intermodulation distortion, the Omnia-6FM displays settings on dual
active matrix color displays. It includes a selectable, four-frequency
high pass filter and phase rotator, an adjustable five-band AGC plus
wideband AGC, a Space-EFX adjustable stereo enhancement algorithm, a
five-band adjustable crossover network, bass management low frequency
enhancement, an over-sampled six-band limiter and a 10/100baseT
Ethernet port and software presets stored on PCMCIA card. Output
section includes dual adjustable composite and balanced analog outputs,
dual AES3 output selectable for 32kHz, 44.1kHz, 48kHz or 96kHz. Inputs
include analog and AES3 synchronizing input. This processor adds a dual
output for digital and analog audio chains. The look-ahead final
limiter conditions audio for the bit-reduced encoders used in IBOC
Digital Virtual Processor
The Digital Virtual Processor uses IDT's fast Fourier transform
(FFT) algorithms, which eliminates the multiband processing approach.
Audio is sampled at 96kHz. The unit uses a 40-bit floating processor.
Version 2 of this processor updates the AGC, FFT engine and limiter.
Basic control is available via the front panel. A software interface is
accessible through Windows 95, 98, NT and 2000 with IE version 5.0 and
above or through a serial modem. TCP/IP control is available as an
option. It includes stereo analog and digital I/O, a BNC wordclock sync
in/out, a 19kHz pilot output, two subcarrier inputs and two composite
The 1100 is a PCI-card application of an Optimod processor suitable
for live streaming and on-demand programming. It offers features such
as two digital inputs with mixing of asynchronous sources, and sound
card emulation that allows Optimod-PC to talk through the operating
system to applications running on the host. Multiple cards can be
installed in a single computer. The processing includes a two-band AGC,
a shelving bass equalizer, a two-band parametric equalizer, a five-band
compressor and a look-ahead limiter plus an internal mixer. I/O
includes an analog input, two digital inputs, analog output, PCI-bus
audio output and a digital audio output.
The DB Max is a level maximizer and audio enhancement processor for
FM and Internet applications. It does not include a stereo generator.
Features include a five-band compressor, automatic gain control,
dynamic and static stereo enhancement and dynamic and static
equalization. Balanced analog, and balanced and unbalanced digital I/O
is standard. Sample rate conversion can be invoked when using digital
inputs. The DB Max can be remotely controlled via GPI, RS-485 or MIDI.
Presets can be saved and loaded to PC cards. The DB Max comes loaded
with 60 presets.
This 1RU multiband digital audio processor uses an eight-bit RISC
micro-controller for the analog and digital circuitry, which includes
24-bit A/D and D/A converters and a range of DSP. The unit includes an
Ethernet module and code to provide a Web-based interface. Control is
also available through an RS-232 port and external closures. Status is
indicated on LED meters and an LCD display. The unit offers wideband
AGC with gating, multiband AGC with gating, multiband limiting with
defeatable look ahead limiting and a distortion-controlled over sampled
clipper. Equalization and composite processing are in development for a
Omnia-4.5 and Omina-3
Both families of processors are available on AM, FM and Internet
configurations and feature a 96kHz/24-bit sampling rate. The 4.5 offers
stereo and bass enhancement features, a five-band limiter and a
two-band AGC. The 3 has a three-band peak limiter, digital audio I/O
and advanced bass management. Both series include a complement of
presets and a PC card interface for software upgrades. The 4.5 can be
controlled through the on-board Ethernet port. An Ethernet port is
optional on the 3. The 4.5 includes a color matrix display. The 3 has a
Optimod 8400HD FM
This processor can provide two independent peak limiting chains; one
for an analog FM transmission and one for any non-preemphasized digital
transmission. It takes into account the differences in analog and
digital transmission processing needs. The processor includes a stereo
enhancer, two-band AGC and selectable five-band or two-band
compression/limiting for analog and digital transmission paths. The
analog transmission path then adds the necessary pre-emphasis and
stereo generation. The digital output offers a look-ahead limiter. The
digital processing chain allows users to insert a high frequency
shelving equalizer before or after the look-ahead limiter.
Digital Band Processor 4
This four-band processor provides processing power for medium-market
applications. It includes a stereo encoder and several plug-ins. The
unit features a wide-band AGC, two or four bands of compression and two
or four bands of limiting. The crossover frequencies are adjustable. It
operates on a 96kHz sampling rate with a 40-bit floating internal
processor. The IDT Advanced Peak Control optimizes the clipping point
to prevent overshoots and distortion. Various presets are available.
The Compact Flash port allows the user to store and load presets. It
includes analog and digital I/O. Models are available for AM, FM and
The Ariane Stereo Audio Leveler design premise is to control levels
while preserving dynamic quality. Placed at the beginning of a
station's audio chain, this product analyzes the variation of RMS
energy of the audio, and then dynamically adjusts as needed to bring
the program audio to the user-specified target dynamic range. If
needed, the unit will adjust levels with its multiband stereo matrix
control system. The XLR I/O can then feed an all-in-one or peak
processor. The four audio bands can be controlled through the
front-panel trimpots. This product is distributed in the United States
by Broadcasters General Store.
This software processor runs on a Windows 98, 2000, NT or XP
operating system and can run on a streaming audio server
simultaneously. It can be used as a processor for Windows Media, Real,
MP3 and other streaming formats. Omnia A/X looks like a sound card to
the host computer, so it's compatible with most applications that use
the wave in/out driver interface. Using about 20 percent of the
resources of a 700MHz Pentium III, multiple copies of the program can
be run. Features include an adjustable wideband AGC and a three-band
compressor/limiter, an HF EQ and low-pass filter and a look-ahead
DBP7+4 in DVP
This processor combines IDT's FFT technology with multiband
processing. It features three stages: a seven-band compressor, a
four-band limiter and final limiter. The design takes advantage of both
processing approaches. The unit can accept several IDT plug-ins,
including a stereo enhancer, RBDS encoder and Dorrough metering. System
latency is 6ms. The unit can store as many as 60 presets and includes a
scheduler to change presets. The front-panel control can be
supplemented with a software interface, modem interface or optional
TCIP/IP interface. It includes stereo analog and digital I/O, a BNC
wordclock sync in/out, a 19kHz pilot output, two subcarrier inputs and
two composite outputs.
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