Intel High Definition Audio: These Cats Can Play!

Two years ago, I sat leafing through music magazines while a mastering engineer prepared my debut CD project for submission to the manufacturer. When he asked if I'd like to pay more for a high-definition master, I asked what the difference would be between the 20-bit HDCD format and a traditional CD. "It's for audiophiles, but many jazz and acoustic labels use it exclusively," he told me. Unfortunately, finances—and concerns about the ubiquity of the format—compelled me to go with standard 16-bit/44.1 CD-quality audio. Given the increasing popularity of the digital home concept championed by Intel and its partners, however, the next time I'm at that relaxed final stage of production, I may spring for high-definition mastering.

Released around the time I was living out my musical dreams in early 2004, the Intel High Definition Audio spec replaced Intel's prior standard, AC'97. As a result, the processor powerhouse has brought not only higher fidelity (up to eight channels at 192 kHz/24-bit quality, compared to AC'97, or six channels at 48 kHz/20-bit), but also new functionality to motherboard audio.

"The whole motivation for replacing the AC'97 controller was that we wanted more capability for things like higher quality playback, 7.1 surround sound, playing multiple audio streams simultaneously and the Dolby logo program," says Chris Schrage, a software applications engineer at Intel's Folsom, Calif. campus. "And it wasn't just for audio—HD Audio provides a high-bandwidth bus that can also support communication and HDMI devices." Indeed, this integrated audio specification, available with the company's Express chipsets, is giving add-in sound cards and hi-fi consumer equipment new competition, ushering in an era of multi-channel playback that may finally move desktop PCs out of the office and on to the coffee table.

Goodbye, Beeps and Boops
In college, I wrote a C program that played Bach's Prelude No. 1 on my PC's system speaker. First, I had to define an 88-note scale using simple ratios to calculate all the notes based on A, or 440 Hz (in the process, I learned to value the beauty of the tempered scale over my brute force mathematical approach—but I digress). How far we've come since those tinny times!

Today, high-quality sound is increasingly central to personal computing. Finally, audio processing has moved past being a soundcard-based afterthought—and straight onto Intel's vaunted Southbridge I/O chipset (called the I/O Controller Hub in the company's new architecture).

From a pro audio standpoint, however, just what do those higher sampling rates mean?

"The dynamic range of 16-bit wasn't as good as the dynamic range on vinyl, so 24-bit gives you a much better range. You don't have to record your signal as hot, and you don't get clipping," says Paul Greyson, a Silicon Valley consulting engineer for Digidesign, a maker of leading recording studio software. "For certain types of signal processing, 192 kHz is advantageous: You can take noise and shape it into forms that are outside where human hearing reaches. That could be useful for internal processing—it could make it easier to write reverbs, for example."

That said, recording engineers aren't necessarily the target market, at least for now. Home theater buffs and gamers are the consumers Intel is wooing most assiduously with immersive audio.

Don't Move, We've Got You Surrounded
While HD Audio enables 7.1 surround sound (meaning consumers can connect up to eight speakers, including a subwoofer), it doesn't fall into the trap of being a technology that only works for tomorrow's content (3D monitors, for example, are orphans in a still-2D world).

"There's not a lot of 7.1 content out there yet, so we're working through the Dolby program to adapt to different sources," Schrage explains. "The Dolby Pro Logic IIx algorithm can process stereo audio and provide data to all the speakers as if it were 7.1." Conversely, if you hanker for positional sound but lack the piezoelectronics to produce it, the Dolby Virtual Speaker algorithm uses a phasing effect "to trick the ear into thinking you have speakers behind you."

As for the other applications HD Audio enables, codecs, to take just one example, are springing up everywhere. At the 2006 Intel Developer Forums in San Francisco and Taipei, Realtek Semiconductor unveiled codecs with content protection technology and the ability to seamlessly switch between Skype VoIP and traditional PSTN.

Other fascinating features include jack detection and jack-retasking technology (enabling true plug-and-play, regardless of which peripheral is connected where) and enhanced voice capture via array microphones, which offer better noise cancellation and beam forming, according to Schrage.

Cutting Cable Clutter
Staying on top of shifting standards and choosing connectivity technologies that are likely to outlast competing approaches is one of the hardest tasks Intel engineers face. This time, however, there's little debate that Intel's made a brilliant choice with HDMI, or High Definition Multimedia Interface, as its technology for ferrying uncompressed video and audio from your PC to your home theater. With its 5Gbps of bandwidth capable of carrying 1080p video and eight channels of 192 kHz audio, a single HDMI cable easily replaces the 14 or so you'd need for, say, 7.1 audio and RGBHV device-to-device connection.

"If you want to have a PC in your living room, HDMI will be the logical conduit for that," says Brett Gaines, senior director of business development for Silicon Image, maker of HDMI transmitters and receivers. "The audio technologies in HDMI 1.3 are a part of new Blu-Ray and HD-DVD disks. Compared to previous compressed audio technologies, this lossless audio is quite likely to drive adoption."

HDMI isn't the only game in town, however. Toslink, Firewire, and S/PDIF (Sony/Philips Digital Interface) are other digital connectivity options vying for consumers' attention.

"The problem with using S/PDIF versus Intel HD Audio as the audio source for an HDMI implementation is that you lose the capability to play 7.1," says Schrage. "Instead, you're limited to two channels, PCM format. Another downside is that the audio and graphics drivers aren't coming from the same source. With the HD audio implementation, both drivers are coming from Intel. And HDMI is intelligent, unlike S/PDIF—it can report back to driver what you're actually connected to. Finally, with a S/PDIF implementation you potentially lose a port—most codecs today have just one S/PDIF output."

Secret Sauce for Software Developers
While a sea change in integrated motherboard audio may be inevitable, it won't be navigated without incident. Developers who embrace HD Audio should know that "in the past, integrated audio has had a reputation for inferior quality," according to Intel media chipset architect Scott Janus in his book, "High Definition Audio for the Digital Home" (coauthored with senior SigmaTel technical staff David Roach and audio measurement guru Wayne Jones). "With the advent of HD audio and improved PC design guidelines," Janus tells me, "some of today's computers offer sound as good as or better than traditional consumer electronics devices."

"I'm not a hardware guy, but I know you're going to have to be aware of clock noise and other kinds of junk in the audio signal," says Digidesign's Greyson. Jitter, zipper noise, clicks and pops are all preventable, however, if developers follow Janus's rules for reducing audible artifacts during mode transitions. These include lessons learned from concert sound systems, which define precise power-up and -down sequences for all connected components. They also extend to PC-specific annoyances such as beep circuits, RESET# signals and modem connection progress sounds from PCMCIA card cages. Developers interested in designing high-quality software and hardware audio products may want to read "High Definition Audio for the Digital Home."

Given the engineering talent Intel has assembled to take integrated audio to the next level—and connect it to consumer electronics through streamlined standards such as HDMI—application developers will eagerly absorb these tricks, and more. The result, after all, will be music to their ears.