Audio Convergence Follows Digital Revolution
Audio Precision is celebrating its 30th anniversary. When asked about the most significant change in audio technology over the company’s history, Dr. Tom Kite, vice president of engineering, said, “The switch from analog to digital—if you look at the first product we made, it was all analog under the hood.”
Vice President of Engineering
Now, he said, what’s of note is the proliferation of different interfaces. “You used to have RCA connectors, and that was it. A few years later maybe you had an S/PDIF connector from your CD player. Then, nothing much happened for a long time. But all of a sudden, boom, we have HDMI, Bluetooth, PDM, AVB, Dante—we have just tons of ways of moving audio around these days.” The proliferation of interfaces affects how Audio Precision designs its instruments.
Tom Williams, vice president of sales and marketing, described Audio Precision’s lineup. “Our flagship product is the 2700 Series. It has the lowest distortion and the best performance of any analyzer in the world. But for the past nine years we’ve been working on the APx family.” The APx, he said, is a platform that can support different digital interfaces and multiple audio channels. And a crucial feature is that it’s easy to use for people who might not be doing audio test eight hours per day.
Vice President of Sales and Marketing
Audio Precision also offers at least two major software releases per year. Last spring, Williams said, the company added rub and buzz and leak detection functionality for electroacoustic test, and in the fall, the company introduced support for impedance magnitude and phase measurement and key Thiele-Small parameters for loudspeaker production test.
Williams noted that the software runs across the APx platform—from a $6,400 APx515 to a fully loaded $40,000 APx586. “If you’re an R&D engineer with a decked out 525, you can write a project that the 515 will run,” he said. The 515 will open projects natively and ignore the channels or signal paths that it doesn’t have. Consequently, R&D can share files with production, often making it unnecessary for an R&D engineer in the United States to take his analyzer to a production facility in China.
The move to digital audio isn’t without challenges. Said Kite, “There’s an assumption among certain people that ‘oh, it’s all digital—it’s perfect, and I’ve got nothing to worry about.’ That’s not really true.” Digital is robust, he said, but long cables can have a lot of roll-off or pick-up noise. And even if the bits are getting from one end of the cable to the other, there could still be problems related to metadata and protocol issues.
“A lot of handshaking goes on when you connect two pieces of equipment,” he said, “and if the handshaking doesn’t work right, then everything can go horribly wrong.” For example, if you use HDMI to connect a DVD player to a TV, the TV must correctly present its capabilities via extended display identification data (EDID). That would include a list of resolutions the TV can handle and audio formats that it can process. If the EDID is not correct, Kite said, “the DVD might well send the TV something it cannot deal with, and what comes out is an awful sounding mess.”
Perceptual analysis is another area of focus for Audio Precision. In 2012, the company announced a Perceptual Evaluation of Speech Quality (PESQ) software option for its APx analyzer, and in May of last year, it added next-generation Perceptual Objective Listening Quality Analysis (POLQA) functionality.
Kite explained that CVSD codecs, for example, are notorious for providing voice quality that’s tolerable—good enough for a phone call—but not great. Distortion is so great that traditional tests involving sine waves tell you nothing meaningful. One approach is to have a roomful of people subjectively judge the codec’s output—assigning a Mean Opinion Score (MOS) of from 1 to 5. PESQ and now POLQA enable an APx analyzer to take psychoacoustic factors into account and assign an MOS objectively.
Looking ahead, Kite and Williams see continuing integration of electronics and acoustics in one box (which is discussed in detail in “Audio Precision VPs cite interface, electroacoustic convergence” at bit.ly/1fw9lXa). The situation, Kite said, “is very different from 20 years ago when you would buy a stereo amplifier and buy a set of speakers separately.” At least in the midrange, he concluded, “that just doesn’t exist anymore.”