ADI fixed-point DSP pursues midrange receivers

After using a floating-point DSP to sew up the market for audio decoders in high-end A/V receivers (AVR) for home theater sound systems, Analog Devices Inc. is now going after the midrange portion of the AVR market with a fixed-point version of the same 32-bit processor.

Called the Melody 32, the chip provides eight-channel surround sound as well as an SRS Circle Surround II. It decodes Dolby Digital-encoded bit streams, Dolby Digital EX, Dolby Pro Logic II, DTS-ES Extended Surround, DTS Neo:6, THX Surround EX, THX, AAC, MP3 and PCM.

"We've chosen the software route," said Ashok Kamath, who manages ADI's audio product line from India. "When a DVD is inserted, the DSP automatically detects the kind of bit stream represented and kicks in the appropriate decoder [stored in flash memory]," he said.

ADI's Sharc DSP has been the darling of high-end AVR makers in Japan, including Sony, Denon, Pioneer and Kenwood, said Mike Haidar, product line director for software and systems technology at the DSP division of ADI.

Brochures for products like the Sony 9000ES DVD player (a $1,000 receiver and MPEG image decoder) use the Sharc name as part of their promotions. The 32-bit floating-point processor provides a higher dynamic range and lower noise floor than the 24-bit processors promoted by Zoran, Motorola and Cirrus Logic, according to ADI.

The fixed-point unit introduced this week provides many of the same advantages as the floating-point unit, though it is aimed at $200 to $500 AV receivers, said Haidar. In an announcement that coincided with ADI's, Kenwood Corp. announced three AV receivers, priced from $200, which use the Melody 32.

Subtle differences

But apart from price, the differences between a 32-bit floating-point audio decoder and a fixed-point unit are subtle, Haidar said. The fixed-point unit has a more difficult time processing computational overflows, he said.

This will show up on the soundtrack of a movie like "U-571," a submarine battle movie in which the frighteningly loud depth charge explosions will seem slightly distorted to a trained ear while remaining thrilling and unnoticeable to practically everyone else. The difference is maybe three or four bits, he said.

"People love 32 bits for multiply-accumulate operations," said DSP industry analyst Will Strauss, president of Forward Concepts Inc. "The floating-point unit provides some 1300 dB of dynamic range. Who needs that?" he said. "But the 32-bit fixed-point unit is just as cheap, maybe even cheaper, than a 24-bit processor."

But though it is now number one in the PC audio business, ADI will have to work hard to displace Cirrus Logic Inc. in the midrange AVR market. Cirrus had approximately 51 percent of the 8.5-million unit AVR market in 2001, according to Forward Concepts.

Yamaha Semiconductor had about 33 percent and Motorola's Semiconductor Products Sector's 56300 series DSP had about 13 percent. Entrenched as it claims to be in the high end of the AV receiver market, ADI's share of the total AVR market was only about 3 percent, Strauss said.

Unlike the telecommunications market, consumer electronics has been doing rather well, Strauss said. The 2002 market for AVR receivers is expected to grow to about 10 million units, reaching 12 million to 15 million units in 2005 if current trends continue.

The Melody 32 platform will decode practically all new digital audio formats and provide bass and delay management, said ADI's Kamath. The accuracy of the decoders is certified by the format providers Dolby, DTS, SRS Labs and Lucasfilm THX.

An evaluation board with a copy of the software and schematics is available for $1,250.

— Stephan Ohr

EE Times