Field Report: Vorsis AP-2000

October 1, 2008

The Vorsis AP-2000 is a five-band AGC/compressor and 31-band limiter with specialized algorithms for bass and voice band processing. Its output feeds will accommodate just about any flavor of FM/HD Radio operation. Transients are gracefully controlled without compromising the long-term texture, levels, frequency response and harmonic integrity of a station's signature sound. The AP-2000 includes the latest development from Vorsis, a division of Wheatstone.

This one does it by the numbers, packing the math power of 19 digital signal processor (DSP) engines. The processing workload is split into a multitude of parallel processes. Independent analog and digital transmitter paths contain their own respective 31-band limiter, VBMS and Voice Master algorithm. Despite its complexities, the AP-2000 amazingly reconstitutes all this information — time aligned analog to digital, phase aligned analog L+R vs L-R and phase coherent across the audio spectrum.

The big bottom

Spy on your program director's car or office radio and it probably has the EQ extremes cranked up. Everyone wants more bass, but that can mean more intermodulation distortion. To that end, the Vorsis Bass Management System (VBMS) was developed to separate and process the bass range independently. The VBMS boosts base while mitigating the effects of IM through mathematical control of harmonics.

Membership into a secret society is not required for full access to the AP-2000. Every feature and control is present on the front-panel LCD display or through a Windows-based software application.

Performance at a glance
31-band fine grain processor
Five- or three-band AGC preprocessor
Oversampled look-ahead limiter or specialized clipper
Voice Master voice distortion management
Ethernet-based remote control
Eight input GPI preset triggers
32kHz - 96kHz digital input
FM/HD Radio delay of up to 10 seconds

Control area

Analog and AES3 audio inputs provide source diversity for fail-over protection in the event of prolonged silence to either path. There are analog outputs with or without de-emphasis, AES3 digital outputs with selectable pre/post diversity delay and with/without de-emphasis. Balanced composite stereo is present on the XLR jacks for a clean, noise-free signal into an FM exciter equipped with balanced inputs. There are also two unbalanced composite stereo outputs on BNC connectors. Jacks are provided for SCA injection and control.

The general purpose interface (GPI/GPO) has up to eight opto-isolated inputs and four outputs that have tested well in high RF environments. A typical application might include remotely bypassing the AP-2000 during EAS tests with a logic return on the transmitter remote control confirming the system status. Convenient front-panel connections include a headphone jack and a USB port for a mouse. A five-port Ethernet hub inside is brought out to RJ-45 jacks on both the front and rear panels.

Getting started is easy. The manual has an 11-step guide to getting on the air. Suggested default settings for most parameters are listed for a good starting point. There is a list of about 70 ready-made presets for various programming formats. Finding that perfect setting comes down to choosing a compromise between clean and loud.

The GUI was designed so navigation is done with no more than two mouse clicks — no more auguring through multi-branched menu trees. It can control any number of AP-2000s over a LAN through VPN tunnels and behind firewalls. Any laptop or desktop computer running Windows 2000 or XP with a CPU speed of 1GHz should perform just fine. The Web interface does not support open ports to the Internet or act as a Web server making it immune to network hacking.

The GUI display is divided into four basic sections: Title Bar, Control Area, Side Bar and Dynamic Displays. Dynamic Displays region includes a frequency-domain graph showing the parameters of the five-band AGC, both FM and HD 31-band limiters and the adjusters for manipulating settings.

On the left hand side of the Dynamic display are a series of four bar graph meters for monitoring input/output levels and processing levels. The Gain Reduction Meter can be selected to monitor a variety of internal processes.

Fast-Fourier Transform (FFT), real-time spectral analysis is available at the click of a button to display the input audio or the processed audio. Various other display parameters such as an oscilloscope representation of the signal, gain reduction graph and control position markers can be selectively added or removed from the display.

Control Area

A large area above the Dynamic Display is the Control Area. Under the Input panel you will find adjustments for selecting analog vs. digital audio sources, engaging the input failsafe feature, independent gain control for the analog and digital sources, balance trim as well as controls for auto mono, phase rotator, Voice Master and the high pass filter.

The auto mono feature, as the name implies, was developed to clean mono content where unintentional artifacts cloud the spatial image. The phase rotator prevents clipping by rearranging the phase of asymmetrical waveforms before they hit the rail. The high-pass filter eliminates low frequency content that cannot be heard on FM and is a source of intermodulation distortion.

A Vorsis exclusive is the Voice Master algorithm. It engages a special voice-specific set of equalization and limiting parameters when it detects mono, narrow bandwidth and asymmetric waveforms. If all three of these parameters are met the Voice Master engages.

The four-band parametric equalizer could be described as a four control node EQ. These fully independent but complementary control nodes can be frequency centered anywhere in the audio spectrum, even stacked. Each node can be adjusted for bandwidth and Boost/Cut. The EQ can be electronically inserted before or after the five-band AGC section.

Core audio processing is divided into three sections: the SST, AGC and compressor. While the AGC and compressor work in a traditional fashion, it is the Sweet Spot Technology (SST) that smoothes processing performance over the long haul, making sure that program content has a consistent sound regardless of the program material. Where AGC and compressor address instantaneous events, the SST acts as the intelligent gain riding control from program element to program element.

The Vorsis/Wheatstone website contains a wealth of information including support documents and software downloads. Jeff Keith, head of the Vorsis design team, has authored a number of white papers explaining the theory behind each algorithm.

Out of the box

Our facility had the opportunity to examine the AP-2000 first hand as well as its predecessor, the AP-1000. It was bench-tested and placed in the broadcast chain of our hot country station for about a week.

Whether you're the intuitive type to simply plug things in and make them work or wait till you've scoured the manual, the GUI was intuitive and easy to navigate. Most controls are mouse-based with some parameters that can be entered via the keyboard. Having every control within two mouse clicks does make it a bit easier to change parameters.

My director of engineering was impressed with the limiter and AGC controls but especially the parametric EQ. The click-and-drag method for changing frequency, gain/loss and bandwidth is pretty cool.

The sheer number of variables that go into shaping the final product can be a bit daunting. Finding the best balance among the various limiters and clippers along the way can take time. In the week the AP-2000 was in chain, many different preset styles were tried with relatively good results.

It's probably impossible to find the perfect sound overnight. Processing is a subjective art and one can become lost after listening intensely for a while. Every audio processor has its signature sound, as does this one. It has some pretty powerful features and evaluating it was like going back to school.

Chestnut is assistant chief engineer at Entercom Kansas City.

Editor's note: Field Reports are an exclusive Radio magazine feature for radio broadcasters. Each report is prepared by well-qualified staff at a radio station, production facility or consulting company.

These reports are performed by the industry, for the industry. Manufacturer support is limited to providing loan equipment and to aiding the author if requested.

It is the responsibility of magazine to publish the results of any device tested, positive or negative. No report should be considered an endorsement or disapproval by Radio magazine.

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