Radio Enters the Digital Domain

Columns From: 1/1/2003 Automotive Design & Production, , Contributing Editor

Motorola’s Symphony digital radio technology isn’t about crowding the airwaves with more stations.

Motorola’s Symphony digital radio technology isn’t about crowding the airwaves with more stations. It’s about better utilizing the existing analog infrastructure while leaving room for improvements in broadcast technology. “The technology we have behind the Symphony system can be applied anywhere within the current or planned radio spectrum,” says John Hansen, strategic marketing director, Driver Information Systems, Motorola (Austin, TX), “including cell phones, walkie talkies, TVs, etc., but we elected to apply the technology to the AM-FM radio market first.”

Audio systems may look the same, but Motorola promises its Symphony digital radio will make them sound vastly different–for about the same cost.

There are 10 digital signal processor (DSP) chips inside a Symphony radio, of which nine are special purpose co-processors supporting a 24-bit core unit that contains the radio frequency (RF) front-end and intermediate frequency (IF) analog interface. All are located on a single piece of silicon, and perform the base-band radio and audio processing for the radio and any add-ons, like a CD or MP3 player. The radio itself is tuned via software, so it can be programmed to find signals mechanically tuned radios can’t, and the variable IF filter algorithm automatically adjusts to either 100 KHz (European) or 200 KHz (North American) channel spacing. Also, by adding a second RF chipset (and antenna) automakers can either increase performance by locking both units onto the same station for better reception, or increase utility by letting the front and rear seat passengers listen to two different radio stations at the same time, while adjusting the “sound space” for each.

Symphony’s parts list is quite short, consisting of one or two RF front-end chips with AM, FM and weather band tuning capability; a digital DSP base band/audio processor; an IF sigma-delta analog-to-digital converter with integrated audio analog-to-digital and digital-to-analog converters. These transfer data between the RF and DSP chipsets. Says Hansen, “one of the capabilities often overlooked is the ability to make changes–changes that can be specific to an automaker or a vehicle line–in a matter of weeks.” As tools improve, Hansen expects these changes to be done in little more than a day, and that third-party developers will create new algorithms aimed at regional problems, like signal scatter in mountainous or urban terrain. “You can’t do that with analog radios,” he says. “Plus, there’s no audio processing algorithm, including Dolby and THX, that doesn’t work with our system.”

The implications for OEMs include the ability to have: (1) one basic chipset, (2) add functions via software to move from a base to a premium unit, and (3) charge a premium for the radio unit. “Sound fields can be put into the system software,” says Hansen, “adding items like equalization, adapting the sound to the environment, or making it sound like there’s a subwoofer in the car, even when there isn’t.” And the claimed improvement in sound quality should make it possible for automakers to use lighter, less expensive speakers while improving sound quality. Space and cost considerations will extend to the radio receiver itself as well.

“There are fewer components in the Symphony digital radio than are in an analog radio,” says Hansen, “and unless someone is pricing to cost, there will be less than a $10 difference between the units in many cases.” The unit also will save space in the instrument panel center stack. “Radio receivers have been filling up much less than the single-DIN space for quite some time,” says Hansen, “and Symphony reduces that even more.” Hansen suggests the radio can fit into the faceplate itself, or be relocated to a drop-down headliner panel.

“Why didn’t we do this five years ago?,” asks Hansen. “Because putting all of this technology into a low-cost imbedded application wasn’t possible back then. Symphony is a meeting of market needs, technical capabilities, and a whole lot of information technology.” Home units will arrive in time for the Christmas 2003 selling season, but the first automotive applications of this audio technology probably won’t arrive until 2006.