On-air processing

August 1, 2003

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.

Resource Guide
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 indicate levels.


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.

Optimod-FM 8300

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 scheduled.

Omnia-6FM, Omnia-6HDFM

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 systems.

IDTImpact Developpement
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 outputs.

Optimod-PC 1100

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.

DB Max

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.

Broadcast Warehouse

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 later release.

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 two-color display.

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.

IDTImpact Developpement
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 Internet use.

Translantech Sound

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.

Omnia A/X

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 limiter.

IDTImpact Developpement
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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