Audio DSP does double duty
By Brian Dipert -- EDN, January 22, 2004
Unwilling to give a key competitor sole access to the new-product limelight, Cirrus Logic introduces the CS49520, which thrusts the company’s high-end audio processors fully into the 32-bit era. (see “SHARC swims toward deeper, more fertile waters,” EDN, Dec 11, 2003, pg 18). Prior-generation Cirrus Logic processors, such as the CS49400, combined a 24-bit DSP core to decode incoming digital-audio bit streams and a separate 32-bit DSP core for postprocessing functions, such as bass management and speaker and channel virtualization.
In contrast, each of the two 32-bit DSPs in the $16.95 (10,000), 120-MHz CS49520 can itself tackle both decoding and postprocessing tasks, according to the company. The DSP cores can, if you desire, run on unique clock domains, and each contains dual MAC (multiply-accumulate) units and a 72-bit accumulator. The cores differ is in their respective associated memory: DSP core A has 160 kbytes of RAM and 384 kbytes of ROM, whereas core B offers 128 kbytes of RAM and 96 kbytes of ROM.
Practically speaking, the memory differences restrict you to running more complex decoding and postprocessing algorithms, such as DTS, Dolby Headphone, THX, and Windows Media Audio Professional only on core A; less memory-intensive algorithms, such as Dolby Digital, Dolby Pro Logic II, and SRS Labs’ Circle Surround II, can squeeze into either core. But why do you need two cores at all? Cirrus Logic’s examples are a bit obscure: One person or group of people auditions an audio source over speakers while another person listens to a different audio source over headphones (ambient-noise reduction doesn’t work that well), or two rooms in the house simultaneously play audio from different sources over different speaker sets (maybe in Bill Gates’ house). The company acknowledges as reasonable your potentially ensuing assumption that a single-core DSP may be on the way, although it’s not ready to discuss details. Cirrus’ strategy, it seems, is to first tackle the more challenging dual-core variant, following it with a simpler single-core chop.
If your audio-processing needs are simpler and less costly, perhaps the $12.95, 90-MHz CS49500 or $14.95, 110-MHz CS49510 will better fill the bill. Due to these processors’ lower speeds, dual-bit-stream decoding is less likely to be feasible; the two DSP cores will instead, as in the CS49400 product family, work in tandem to decode and postprocess a single bit stream. All three chips, available in 144-pin LQFPs, are now available in sample quantities and are scheduled to enter volume production during the second quarter.
Cirrus Logic, 1-512-851-4000, www.cirrus.com.
