Two-channel microphone confronts commotion
By Brian Dipert -- EDN, May 2, 2002
If you're recording music, a left-plus-right microphone makes a lot of sense. But why would you need to use one with your PC? That's what I thought, until I visited Analog Devices' booth at February's Intel Developer Forum (San Francisco). The company partnered with microphone manufacturer Andrea Electronics, which supplied a two-microphone array suitable for placement atop a computer monitor. The demo highlighted Analog Devices' next-generation SoundMax Cadenza software, due out this quarter, and its dual-microphone-preamplifier-equipped AD1981B audio codec, whose baseline single-channel variant the company introduced last August at $1.80 (100,000).
Cadenza integrates Andrea Electronics' PureAudio and DSDA (Digital Super Directional Array) noise-cancellation algorithms. PureAudio detects and deletes repetitive background noise, such as computer-fan hum or ultraviolet-light buzz. You can apply this algorithm to any microphone. When Cadenza receives a two-channel audio source, though, the real magic begins. Recall that sound-stage-expansion algorithms, simplistically speaking, exaggerate left-channel-versus-right-channel audio differences (see "Decoding and virtualization bring surround sound to the masses," EDN, Oct 25, 2001, pg 63). DSDA works in reverse, suppressing audio information that isn't common to both channels and thereby creating a narrow reception cone of microphone sensitivity.
DSDA focuses on a user's voice and cancels out repetitive or random noise outside that signal. The technique works well if the demos are any indication of the final product's performance, and you can apply the approach to videoconferencing, Internet telephony, voice recognition, and other audio-input-centric computer applications. DSDA Version 2 incorporates dereverberation techniques that minimize the audio degradation caused by a speaker's voice bouncing off walls, ceilings, desktops, and other reflective surfaces. As such, it enables a user to more comfortably sit farther away from the microphone array.
Analog Devices, 1-781-329-4700, www.soundmax.com.
Andrea Electronics, 1-631-719-1800, www.andreaelectronics.com.
