Oak backs AC97 spec with audio chip

Electronic News, June 17, 1996 by Andrew MacLellan

Mountain View, Calif.--Oak Technology demonstrated its support of the new Audio Codec '97 (AC97) specification--unveiled last week by a five-member consortium of board and chip vendors--with the introduction of the OTI-611 digital audio accelerator.

The AC97 specification, developed by Intel in collaboration with Analog Devices, Creative Labs, National Semiconductor and Yamaha, sketches an architecture designed to enable advanced audio, such as Dolby Surround AC-3, on mainstream PCs by splitting digital and analog functions onto two chips. The OTI-611, expected to be available in 3Q96, will address the digital portion of the specification and will be followed early in 1997 by the OTI-612 analog audio/communication codec, according to Oak.

"I think the AC97 announcement is good for alerting the industry that this type of approach is going to deliver compelling audio," said Ken Boyce, manager of Oak's audio and communications business unit. "But most importantly this spec will bring uniform audio across multiple platforms."

A reversal of the trend toward integration that is being pursued almost universally across the semiconductor industry, the AC97 standard separates digital from audio in an effort to reduce the noise on analog circuitry while affording more room on the chipset for the growing menu of emerging digital functions.

"AC97 is a multi-vendor audio codec specification which creates a strong foundation for modular digital acceleration of audio and communications functions on the PC," said Bert McComas, president of multimedia market research company InQuest. "It is favorable for applications which use host-based signal processing, hardware acceleration or both. In addition, AC97 will permit a more rapid transition to PCI audio by enabling designs which can support both PCI and ISA."

The specification, which is available through Intel under a royalty-free reciprocal license, calls for adoption of a 7mm x 7mm, 48-pin analog component which is isolated from off-chip noise and placed closer to the audio connector for better sound quality. The analog codec is defined as a 16-bit, full duplex component with a fixed 48-kilobit sample/second rate.

The digital chip controller, with a 5-wire, bi-directional, time-division-multiplexed audio codec-link interface, is then able to shed high-fidelity linear circuitry and pack more digital functions on-chip for acceleration of applications such as digital versatile disk (DVD) players and interactive 3-D games. The scalable architecture also is claimed to interface with any bus, including platforms using the Universal Serial Bus (USB) and 1394 specification.

Intel claims the new architecture, because of its simplified analog circuitry, costs about the same to manufacture as traditional one-chip devices.

Samples and evaluation boards based on Oak's OTI-611 chip will be available this fall. Volume pricing is expected to be less than $30, although Oak said it is still qualifying the part. Other companies, such as Aztech Labs, ESS Technology and Crystal Semiconductor, are also said to be readying chips based on the AC97 specification for sample shipments later this year.

"What's important for us to get across is that AC97 validates the overall approach we've been taking," said Oak's Mr. Boyce. "We believe we have a flexible, immediate solution to meet AC97 prior to products that are designed specifically to meet the pin-out of the AC97 spec."

According to Oak, the OTI-611 IC consists of a programmable DSP with an integrated PCI bus master interface and will support Microsoft's DirectSound API, wavetable synthesis, multi-channel digital audio mixing, 3-D positional sound and multiple audio and communications codecs. Oak is also shipping its HSPV34, 28.8-kilobit/second software with the OTI-611 chip to enable OEMs to offer both host-based processing (HSP) V.34 and digital simultaneous voice over data (DSVD) V.70 modems.

The analog OTI-612 dual audio/communication codec, which is under development, is expected to exceed the AC97 specification by including additional telephony functions as a standard feature.