I have four decades of engineering under my belt, but it was at the dawn of my career that I learned the importance of audio processing. I cut my teeth in my early teens on Gates and Collins tube limiters and later the venerable “Max” brothers, the CBS Audimax and Volumax. In my post-grad years I worked with the CRL AM-4S stack, multiband processors like the DAP and Optimod as well as custom solutions devised by various station engineers.
Many members on my low-power broadcast enthusiasts website HobbyBroadcaster.net have used the Inovonics 222 AM compliance processor. One high-end Part 15 transmitter manufacturer not only recommends it but considers it their de facto standard audio processor.
|Details of crossover frequencies for the three-band compressor.
With that in mind I was champing at the bit once I heard about the release of the Inovonics INOmini 223 multimode audio processor and wanted to put it through its paces.
Retailing for $990, it is marketed for use in US/NRSC AM, worldwide AM, shortwave, U.S./Europe monaural FM, TIS and analog SCA applications. Company founder Jim Wood is not only a supporter of low-power radio but also a member of my site’s forum community and was instrumental in arranging for an evaluation unit.
The INOmini 223 represents the digital evolution of its predecessor. This versatile processor is packaged in the company’s new “rack pack” one-third-rack-width enclosure, allowing several INOmini series devices to be mounted in a single shelf 1 RU high.
The rear panel is equipped with standard XLR connectors for audio input and output; there are dual coaxial power connectors allowing multiple 12 VDC INOmini series devices to share a common switching mode power supply as long as their combined current draw is below the power supply’s rated maximum. The rear also contains a strain-relief post to wire-tie the power cables to prevent accidental disconnections.
Thanks to application-specific integrated circuits, there’s quite a bit of power contained in this pint-sized unit. This DSP processor consists of an automatic gain control stage combined with a three-band compressor with adjustable crossover points followed by a lookahead limiter. Depending on the selected operating mode, the output pre-emphasis and filtering is adjusted for its intended application.
Initial setup was a snap, with the factory-supplied default settings serving as a starting point. Besides the ability for processing AM NRSC 10 kHz standard audio, the INOmini 223’s AM cutoff frequency is adjustable to 5 kHz, 7 kHz and 9 kHz. The processor presets also feature appropriate processing settings intended for FM SCA and Traveler’s Information Service applications at 5 kHz in addition to monophonic FM processing for Europe and U.S. standards at 15 kHz. A bonus is that the processor can be used in studio configuration, allowing full-bandwidth audio for processing for tasks such as remotes, microphones, etc.
The multifunction LCD display makes it easy to monitor and adjust the processing blocks. Several scale legends are silkscreened on the front panel for use with of the certain measures. Functions such as the AGC operating window and gain reduction levels, compressor and limiter drive, crossover and EQ adjustments, pre-emphasis and relative asymmetrical modulation can be displayed. More utilitarian functions like application mode, firmware revision, alarm, operate/proof and system defaults modes are accessible through a hidden menu setting. Adjustable system parameters can be manipulated easily with the combined rotary pushbutton knob next to the display screen. A headphone jack rounds out the front panel.
“Because things in DSP are so easy, it was a simple matter to make the processor into something more than the 222 originally was,” Jim Wood told me. The older 222 required discrete component changes to change cut-off frequencies while this same functionality is accomplished digitally in the INOmini 223. The front-panel USB connector not only allows for improvements through firmware updates but an advantage in custom-tailoring the unit should an operator need a parameter considered outside of the norm.
|Inside the Inovonics INOmini 223.
The gated AGC stage sports variable speed windowed operation with a ±15 dB operating range, assuring subsequent stages operate at their optimum. Within a smaller ±5 dB window the gain change occurs slower than when a more substantial amount of gain control is required. This is reminiscent of how I would envision an Audimax would operate had it been developed in today’s digital age.
The triband compressor provides flexibility in creating a signature sound not only by adjustable crossover frequencies but also varying its drive. The display indicates the drive to this stage’s middle band via the selectable real time bargraph.
In essence the limiter has two controls that determine how much it interacts with program processing. Similar to the compressor drive, limiter drive determines the amount of signal being applied to this stage in the processor. Release time operates in a dual-platform mode with very quick release from a peak value to average program levels and a slower release from average value to full circuit gain with no limiting applied. Limiter release timing is adjustable using the Smooth versus Loud control, a manufacturing decision that was made to prevent the operators from getting themselves in trouble. The lookahead limiter also has the advantage to not requiring the need for clipping to take place in the audio path.
The output of the INOmini 223 supports upwards of 140 percent positive modulation in the operating modes for AM broadcast. A selectable display mode displays a dual bargraph, simultaneously showing positive and negative modulation, which may prove handy as a confidence monitor for comparison against your off-air monitoring.
My testing consisted of playing a variety of audio programming through the processor connected to a carrier current AM transmitter, while monitoring the off-air product using a commercial modulation monitor. I decided to duplicate this experience to share with others via video.
My bench test video setup used a three-minute WAV audio file consisting of jingles and song segments with track durations less than 30 seconds each. The under 30-second length was chosen to prevent triggering a copyright violation as short song segments are usually allowed for demonstration use under Title 17, Section 107 (fair use). Each audio selection was mixed to a single audio file with Adobe Audition. The test audio was played into an Audioarts AIR-1 console into the INOmini 223. The output of the INOmini 223 was connected directly to a 10 W Radio Systems TR-6000 AM transmitter, whose off-air signal was monitored and recorded using a Belar AMM-3.
Developing a sonic signature outside of the INOmini 223’s defaults is accomplished by altering the Smooth versus Loud setting for density control in addition to the post-compressor bass and higher-frequency equalizers as they perform in concert with the three-band compressor’s crossover frequencies.
I noticed that even when operating at its highest density settings, the INOmini 223 doesn’t have the busy sound/listener fatigue factor familiar to those running the older 222. Dynamics can be adjusted from very aggressive to a more open sound.
During the on-air bench testing I ran the INOmini 223 through its operating modes and pleasantly discovered that mode changes takes place immediately with no reboot necessary. With no noticeable latency your station’s talent won’t be thrown off by listening to the off-air processed signal.
Inovonics INOmini 223
Multimode Audio Processor
+ Versatile multiple mode audio processor for AM, FM and studio uses
+ Look-ahead limiter reduces distortion products
– No dayparting
– No multiple presets storage
For information, contact Gary Luhrman at Inovonics in California at (831) 458-0552 or visit www.inovonicsbroadcast.com.
Special applications haven’t escaped the design of this processor. The INOmini 223 easily handles unbalanced audio for applications such as campus AM where they may be using consumer equipment. Jim’s firsthand experience with a California-based college campus broadcaster and past TIS applications served as inspiration for the onboard 30 dB output pad slide switch internal to the processor.
The supplied manual is written clearly though I’d bet the majority of engineers could get up and running simply by exploring the menus and running a signal through the processor.
While the processor stores the current active settings, some users might miss the lack of multiple presets storage or daypart ability. I don’t consider either of these deal-breakers because where can you find a versatile three-band processor like the INOmini 223 for under $1,000?
Because it uses modern surface-mount technology, most independent or group engineers aren’t going to perform self-service. Inovonics provides the INOmini 223 with a three-year warranty in the unlikely event the unit requires repairs beyond that of a firmware update.
Jim mentioned to me that the older 222 would remain available in the product line for a while longer although it’s expected that stations would opt for the additional performance afforded to them by the latest addition to their product line.
The INOmini 223 allows a station to reap the rewards of today’s digital technology thanks to this feature-rich, budget friendly processor.
Bill DeFelice is former chief engineer of WMMM(AM)/WCFS(AM) in Westport, Conn., and webmaster of the History of Westport Connecticut Radio. His Part 15 website is HobbyBroadcaster.net.