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Lossless coding comes to portables

With more widespread use of MP3- player docking stations, consumers are increasingly finding that the sound quality from portable devices does not match that of CD-sound, according to austriamicrosystems. Consequently, AMS has introduced the AS3532 mediaplayer IC that will handle lossless-compression music content while still operating within a 5-mW limit. The intention is “to bridge the gap between the audio experience of music phones and Hi-Fi home audio devices,” AMS says. Designers frequently base portable players on a processor core such as an ARM—perhaps paired with a DSP core—that performs the MP3 decompression in software. AMS has retained an ARM core as controller, but has built an optimised hardware audio engine to carry out the decompression. Roberto Simmarano, the company’s senior marketing director, communications business unit, says that when you move from lossy to a lossless codec, the amount of processing required from a programmable DSP architecture rises sharply: more operations at a higher clock rate mean more power. Within its 5-mW power budget, the IC can process 24-bit content at a 192-kHz sample rate—many portable devices today are limited to 16-bit data at 44.1 or 48 kHz. The audio engine executes the decompression and playback of most popular compressed audio formats, like MP3, WMA and AAC, for the least amount of power consumption with zero CPU load. The audio post-processor implements an ASRC (asynchronous sample-rate converter) with neartransparent quality that achieves a range of 136 dB using a multi-pass algorithm, a multi-channel mixer with limiting function and a 10-band graphic equaliser. Three sets of I2S outputs can independently control stereo speakers, the associated subwoofer, and headphone or line outputs, or can act as multi-channel audio outputs. A stereo PDM digital microphone fills out the audio requirements for new-generation mobile phones. Interfaces that are part of the AS3532 can support either peer mode to a baseband phone-IC or a “Black Box” companion music sub-system. In the latter case, the IC provides direct support for a variety of removable and embedded flash-memory types. AMS supplies the chip in a 6
6-mm CTBGA package. Simmarano declined to discuss pricing, as he is marketing this part directly to tier-1 and -2 phone handset makers; further related parts will address other sectors of the audio industry.

austriamicrosystems, www.austriamicrosystems.com.