TI pushes 48-bit DSP for consumer audio apps

By
iApplianceWeb
(08/26/02, 05:48:35 PM EDT)

SAN FRANCISCO - Texas Instruments Inc. will announce this week a 48-bit, fixed-function audio DSP for high-end audio-video receivers, DVD players and audio component systems. The TAS3103 is among the first DSPs with a 48-bit word width for consumer audio applications.

Analog Devices Inc. offers a DSP with a 32-bit word width for AV receivers, while Cirrus Logic Inc.'s and Motorola Inc.'s audio DSPs have utilized 24-bit word widths.

These 24-bit are running "double precision" to avoid doing damage to an audio signal, said Ryan Reynolds, digital audio marketing engineering with Texas Instruments. "It's in the multiply-accumulate cycles: They need to multiply twice to get a 48-bit result," he said. "That means a 24-bit processor must run four times as many cycles."

While high-end analog-to-digital converters use a 24-bit word width to capture audio signal amplitudes to a 120-dB dynamic range, near the limited of human hearing, DSP math requires a wider word width. A 24-bit multiply-accumulate operation will introduce distortion unless it has a larger carry-over space, said Reynolds. "Twenty-four-bit processing does damage to the signal - it degrades the audio," he said.

Forty-eight-bit math implements a 76-bit filter, he said. The previous generation of TI processors used a 32-bit DSP to implement a 56-bit filter. Operating at 135 MHz, the 48-bit audio device implements 540 million instructions per second (Mips) to process algorithms for complex audio effects. The 48-bit processor works with audio sampling rates up to 96 kHz on one side, and outputs directly to TI's digital amplifiers on the other. It performs dynamic range compression and expansion - which keeps neighbors happy during late night viewing - and simulates concert hall effects. Though it is not designed for multichannel decoding like Dolby Digital stream, Reynolds said it will perform surround-sound processing and 3-D effects with rear-channel delays.

In addition to 3-D surround-sound algorithms, the TAS3103 will implement software volume, bass and treble controls, and parametric and graphical channel equalization with up to 16 bands of independent equalization per channel. A spectrum analyzer is also integrated and can be configured as a five- or ten-band analyzer, or as a two-channel stereo VU meter. The TAS3103 chip processes three channels; two are required for a six-channel system, Reynolds said.

Reynolds said that receivers utilizing the 48-bit DSP will be demonstrated at the Consumer Electronics Show in Las Vegas next January. The device is not targeted at professional audio equipment, but at high-end AV receivers. It costs $2.50 each in 50,000-piece lots. "Five-hundred Mips is a nice amount of processing for the size and the price," Reynolds said.