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To: Flint who wrote (12339)	9/27/1998 6:08:00 PM
From: Gambit	Read Replies (1) \| Respond to of 13925

From EEtimes eet.com Think we will see 24bit 96kHz in computers any time soon? : ) Adam- ------------------------------- Posted: 9:00 p.m., EDT, 9/24/98 Digital audio gets a tune-up By Stephan Ohr SAN FRANCISCO — Once 16 bits of dynamic range and a 44.1-kHz sampling rate was the best technology audio engineers could muster to digitize a musical waveform, but advances in semiconductor technology have given professional audio-mixing consoles the benefit a 24-bit dynamic range and 96-kHz sampling rates. New parts scheduled for introduction at the Audio Engineering Society (AES) convention next week will undoubtedly drive that assumption home. Cirrus Logic Inc.'s Crystal division (Austin, Texas) will introduce a sample rate converter circuit designed to synch any kind of digital audio with a 96-kHz clock. The part is intended for mixing consoles that must blend the disparate inputs of digital-audio recorders, Compact Disc players and DVD players. Burr-Brown Corp. (Tucson, Ariz.) will demonstrate continued strength in audio amplifiers and converters, while Motorola Inc.'s Semiconductor Products Sector (Austin, Texas) will demonstrate a new version of its DSP56300 audio DSP. Quite apart from AES, Tripath Technology Inc. (Santa Clara, Calif.) will be demonstrating new versions of its digital amplifier technology in New York later next week. The CS8420 being introduced by Crystal incorporates a digital audio receiver and transmitter. Synchronizing signals from 8 to 96 kHz, Crystal says this is the only device that will capture all audio sample rates used for broadcast, compact discs, PC audio, movie soundtracks and professional audio-recording systems. In operation, the device will synchronize any input signal with any chosen output. The device is configured for a variety of inputs, including those conforming to AES/EBU pro-audio standards, and S/PDIF consumer standards. The sample rate converter reduces the size and complexity of audio-mixing consoles, enabling them to piggyback on a PC or Apple Macintosh host, said Crystal staff scientist Steven Harris. The device also simplifies the clocking architecture of the mixing console by reducing the number of required clocks. The CS8420 is the latest addition to Crystal's line of professional audio ICs — a line that includes A/D converters, D/A converters, codecs and DSPs. But for its digital-audio target, the DSP56364 introduced by Motorola would be another entry in the category of 100-Mips, $5-DSPs now populated by products from Texas Instruments Inc., Analog Devices Inc. and Lucent Technologies. What makes the Motorola product different is its consumer-audio target. It will support a variety of audio-decoding algorithms such as Dolby ProLogic, adaptive-speaker equalization and bass enhancement. The device will also support 3-D "Virtualization" algorithms in PC games, said Valerie Hase, manager of Motorola's digital-audio operations. The DSP56364 is actually a stripped-down version of the DSP56362, a 100-Mips, $20 part introduced at the Consumer Electronics Show in January. That part had a larger on-chip memory and available firmware for more complex algorithms like Dolby Digital, DTS and MPEG-2. Both the 364 and 362, however, have design wins among consumer-audio equipment manufacturers, said Hayes. Burr-Brown's entries at AES include the PCM1704, a 24-bit audio DAC. The BiCMOS part uses a sign-magnitude conversion technique rather than sigma delta. The sign-magnitude technique provides a bit more linearity for low-level signals, said Mike Centorino, Burr-Brown's audio product line manager. The part has a 112-dB dynamic range, and a total harmonic distortion-plus-noise (THD+N) figure on the order of 0.0025 percent. Also to be shown at AES is Burr-Brown's OPA604 and OPA627 FET-input op amps. The 627 has a 55-V/µs slew rate and a 0.00003 percent THD+N figure. Burr-Brown converters and amplifiers are used in the reference designs put together by Motorola, confirms Centorino. In New York later next week, TriPath Microsystems will demonstrate new versions of its digital-audio amplifier ICs. The parts are not "Class D." Like new-generation Class D amplifiers, the TriPath components use switching amplifier techniques to reduce amplifier size and power dissipation. Unlike Class D, which relies on fixed switching frequencies, the TriPath's devices operate "spread spectrum" at frequencies well above 200 kHz. Because the switching harmonics are easy to filter and are well outside the audio range, TriPath claims a greater linearity, a lower noise floor, a greater dynamic range and a flatter frequency response for audio signals.