It’s not my intention to alienate anyone, but I think many broadcasters will agree that while video is usually a given, audio will “get” you every time. For the past three decades, I’ve tried to accumulate as much information as I could about professional audio. I think that I’ve probably only scratched the surface, but I do know how complex professional audio systems can be. I also know that a small arsenal of tools is required to maintain, test and evaluate a broadcast facilities’ audio infrastructure, both analog and digital.
Audio Precision, a leading audio test system manufacturer located in Beaverton, Ore. is now offering their ATS-2 test and measurement system to help simplify the measurement and testing process, (and, in the process, maybe expand your own capabilities).
The ATS-2 is a 2-RU unit, and can either be mounted in a rack or placed on a bench top. It weighs about 15 pounds and operates on AC voltages from 110 to 240. The all-metal chassis has a traditional broadcast look and feel, but the unit’s features immediately announce its modern purpose.
On the front of the device, you’ll find four basic sections: Digital Input, Digital Output, Analog Input and Analog Output. The Digital I/O sections each include an optical connection (TOSLINK), and unbalanced input (BNC), and balanced three-pin XLR connectors for inputs I and II. The Analog I/O sections include BNC input and XLR connectors for audio channels A and B. There’s also an amber-colored power indicator LED.
The rear is populated with the power connector-fuse-power switch assembly, headphone jack, fan exhaust, a DB-25 connector for APIB Interface, DB-9 aux control input and output jacks, output monitor jacks (BNC) for both source and function channels I and II, Sync/Ref in BNC, Trig in and out BNC’s, and a ground connector.
The ATS-2 uses a PC interface to display and control signal generation and testing.
For my evaluation purposes, I was supplied with a USB-APIB adaptor, along with the ATS-2, allowing USB 2.0 connectivity between my laptop and the ATS-2. With the PC control, all tests can be graphically illustrated, printed, and reports and data can be easily exported for word processing or further analysis.
The ATS-2 has two signal generators, one each for analog and digital. Signals include: sine wave, mono, stereo, phase-shifted, tone bursts and dual. Noise, square waves, and special waveforms (including polarity, pass-thru, and user-defined or predefined multi-tone signals) are also available.
For measurement, the ATS-2 comes configured to perform the level, frequency, noise, THD+N, crosstalk, and phase measurements. Detector and filter selections include band limiting, band pass, weighting, and notch, and the detectors may be RMS, average, or peak for differing measurements. The spectrum analyzer test function is an FFT (Fast Fourier Transform) that generates frequency domain tests with selectable acquisition times, along with windowing and averaging functions. The output can be displayed in terms of either frequency or time.
The multi-tone analyzer test uses selected multiple tone signals with FFT analysis to capture a complete set of performance parameters in less than a second. Measurements include jitter, pulse amplitude, word width, bit activity, sample rate and high-level decoded status bits. A performance option is available (as tested) to increase bandwidth to 120 kHz and allow digital interface signal measurements, including waveform display and eye pattern tests. There’s an interface analysis test that’s used to examine the digital signal in great detail, including amplitude histograms, pulse width histograms, bit-width histograms, and jitter histograms. The harmonic analyzer function is used to monitor harmonic distortion products. All sweeps and graphs can be customized and plotted against each other. By using a powerful scripting language—AP Basic—multi-step test sequences can be automated. Self-running tests can confirm conformance to pre-defined parameters, with reporting in simple results or via multipage graphical reports.
If your testing needs should exceed a basic two channel stereo audio configuration, outboard switchers can expand the number of available test channels in groups of 12, and PC-based AST software allows easy sharing of test data and reports across multiple locations.
Setup was very easy, as I only had three cables to connect: the power cord, APIB interface cable and a USB cable. When PC-driven equipment arrives here, it’s always an adventure, usually involving running down IP addresses from someone or calling in my IT guy.
However, on rare occasions, it can sometimes be a simple task. This was the case with the Audio Precision device. I simply connected the main power cord, hooked up the 25-pin APIB cable between the ATS-2 Chassis and the small USB adaptor, connected the USB cable between my cheap laptop and the USB adaptor, and booted up the PC. After the computer came up, I noticed a blue power LED on the USB adaptor (evidently the adaptor gets its power from the PC). Finally, I powered up the ATS-2. At that point, my PC told me that it saw the USB device, but couldn’t connect to it. I decided that it was probably time to install the AP resources disk included with the unit. After the install, setup was easy and quick. In no time at all, I had a new icon on my desktop—ATS 1.60. And after double clicking this icon, the USB adaptor started clicking (audibly) and the software was off to a good launch.
When the application opened, the screen took on a familiar Windows’ appearance: with “File,” “Edit,” “View,” and the like across the top. However, there were also a host of new test function icons under the traditional tool bar.
Double clicking on each of these opens a window, providing access to each test or feature. There are also five page tabs at the bottom of the screen that allow different pages to be created and saved for quick access. Although the unit seemed simple enough to operate, the sheer number of tests and windows did seem a bit overwhelming.
The next step was to actually do some audio testing. I used my MiniLyzer test generator to provide pink noise at –4 dB, feeding this analog source into the ATS-2.
Double clicking on the ATS-2’s FFT Spectrum feature opened up a familiar spectrum display, along with a setup window the left. By using the setup function, I was able to select my external source from a list of options, and was able to select all of the test parameters, including scale options, display values and input values. After the options were all selected, I pressed the big green “Go” button, and the test process began, and quickly completed. The graph was accurate with regards to my little test tool, and some quick checks along the frequency spectrum with my Tektronix TDS-210 scope confirmed that the levels were indeed correct. It should be noted that I don’t have an audio test lab at my disposal—just the common tools that would be found at most TV stations; however, math is math.
My next order of business was to perform some AES digital audio tests. After connecting our program line AES audio feed to the unit, I opened up some of the digital applications. By using the Digital I/O and Status Bits screens, I was able to display and evaluate individual bits of information, including jitter, peak, format, data rate, active bits and error flags (including confidence, lock, coding and parity).
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Audio Precision | 800-231-7350 | www.audioprecision.com I’m happy to say, my station audio looked pretty good when screened by the ATS-2. Using the eye pattern, histograms and other digital measuring tools, I was able to do some pretty intricate digital audio evaluation, including frame edge roll-off, along with bit/word level measurement. Another feature of the ATS-2 system is its ability to run remote, short duration (3 second) tests.
Just out of curiosity, I downloaded Audio Precision’s free High Speed Tester (HST) 2.0 application and installed it on my PC. Once I opened the application and typed in the serial number of the ATS-2, it connected up just like clockwork. By using the start/stop control feature at the top of the screen, I started the pre-configured test.
Actually, I was having so much fun that I forgot to connect a source to the unit. (This was apparent when the test screen results came up and I’d failed all but three of the 13 assigned tests.)
After setting up the unit to perform some tests with sources I selected, I again performed the HST with very different results—everything passed. I should note that AP offers different versions of their HST for equipment manufacturers and broadcasters.
For several weeks, I kept the unit hooked up in my office and tried most of the tests. Every time I used the Audio Precision product, everything worked perfectly. The software and hardware proved to be bullet-proof with respect to ease of operation. Although I’m quite certain that I did not use the ATS-2 to full potential, I take my hat off to the AP engineering staff for providing the industry with such a valuable and useful tool. They were most helpful when I contacted them, and I’m convinced that they certainly know what they’re doing when it comes to professional audio. In my estimation, ATS-2 is the perfect combination of power and simplicity.
Joey Gill is chief engineer at television station WPSD in Paducah, Ky. He has been with the station for 25 years and has worked in broadcasting since 1977. He may be contacted firstname.lastname@example.org.