Out in Front: July 18, 1996

Five PC industry leaders have developed Audio Codec '97, a specification for audio-codec ICs. The five developers—Analog Devices (Norwood, MA), Creative Labs (Milpitas, CA), Intel, National Semiconductor (Santa Clara, CA), and Yamaha (Buena Park, CA)—developed the specification to address the problem inherent in incorporating high-quality audio into PCs with performance comparable to that of CD-ROMs: Audio-codec ICs place a significant quantity of noise-inducing digital circuitry alongside sensitive analog circuitry. The problem gets more difficult as the digital complexity increases for effects such as 3-D audio, yet the analog performance must still be "high fidelity."

AC '97 resolves this problem by splitting the codec function into two ICs with a standardized interface between them. This approach not only optimizes analog design, but also lets designers choose a digital IC from one vendor and an analog IC from another with assured connectivity.

AC '97 specifies a baseline function for the analog I/O, in a 7×7-mm, 48-pin device; it also lets you combine a 64-pin component with other functions. The digital controller can provide just basic functions or expand to 3-D sound, accelerators, multiplayer gaming, and synthesizers or digitally driven sound enhancements.

AC '97 allows the digital controller to be compatible with PCI, Universal Serial Bus, ISA, IEEE 1394, or other buses. Alternatively, you can incorporate the controller into a larger multifunction controller.

The two ICs communicate via a five-wire path, with clock, sync, input, output, and ground links. The baseline specification defines all interface and control registers and provides four line-level stereo inputs and two line-level mono inputs. It also defines support for 18- and 20-bit audio, four- or six-channel output, loudness and tone control, and other basic audio functions.

The five AC '97 specifiers expect to unveil the first devices to support the spec by this fall. Other IC vendors, such as Aztech Labs (Fremont, CA), Crystal Semiconductor (Austin, TX), ESS Technology Inc (Fremont, CA), and Oak Technology Inc (Sunnyvale, CA), also support the specification. The companies are offering the specification under a royalty-free reciprocal license basis through Intel.

—by Bill Schweber

Intel Corp, Santa Clara, CA. (503) 264-0930; bill_piwonka@ccm.jf.intel.com; www.intel.com/pc-supp/platform/ac97/.