Audio: Not what it used to be
Martin Rowe, Senior Technical Editor -- Test & Measurement World, 7/1/2006 2:00:00 AM
Once upon a time, the word "audio" conjured up thoughts of high-quality sound delivered by dedicated home-stereo systems. "Portable audio" referred to a transistor radio or a Sony Walkman. Today, it seems like every pocket-sized consumer product has audio, with iPods and MP3 players leading the way. In many homes, the living room stereo is now an iPod placed into a speaker/amplifier system.
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| The APx585 audio tester is designed for ease of use. Courtesy of Audio Precision. |
The change in consumer audio from analog to digital and from home-based systems to portable units has brought profound changes in the testing of consumer audio products. Cost is now the driving force in audio testing.
"Testing of consumer audio product varies from zero to 100%," said Bruce Hofer, chairman of Audio Precision. That is, some contract manufacturers of MP3 players may perform numerous tests on production players, while others may not test audio quality at all.
Graham Boswell, sales and marketing director at Prism Sound, echoed Hofer's sentiments. "There's enormous price pressure today," he said. "I've seen large companies try to perform audio tests with PC sound cards." Boswell pointed out that sound cards lack calibration, have limited performance, and have higher noise floors than audio testers. "Noise floors in sound cards can run into tens of millivolts, which is as much as four orders of magnitude higher than on audio testers."
Audio products such as MP3 players, USB audio devices, and TV set-top boxes rely heavily on digital signal processing. No longer does audio travel as analog signals, but rather as digital data streams. The result: Engineers have less knowledge about analog circuits than they used to.
"Analog isn't taught the way it once was," noted Hofer. "People know how to use a scope and a DMM but don't appreciate the power of the frequency domain." Boswell has observed the same trend, but reports some success at getting engineers to look at the frequency domain.
Part of the reason that the FFT is making a comeback is because audio tester software is easier to use than it once was. PCs are now powerful enough to perform frequency analysis in real time, making spectral plots easily attainable. Hofer noted that software helps people set up tests correctly and makes information available to engineers and test operators.
High-quality audio isn't dead—far from it. "The audio CD raised our expectations for sound quality," said Hofer. Thus, makers and users of professional audio products and high-end home equipment still perform rigorous audio-quality testing (Ref. 1). The same applies to automotive sound systems (Ref. 2). New cars now have eight or more speakers, each with unique equalization based on model and interior options of a vehicle.
Hofer notes that as people get used to Dolby 5.1 surround sound in home theaters, they may want it in their cars, too. He would not be surprised if some SUV's began offering movie sound system options in the future.
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