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, the company has introduced the AS3532 media-player IC that handles lossless-compression music content and operates within a 5-mW limit. The company aims to bridge the gap between the audio experience of music phones and high-fidelity home-audio devices.

Designers frequently base portable players on a processor core, such as an ARM—perhaps with a DSP core—that performs the MP3 decompression in software. Austriamicrosystems has retained an ARM core as a controller but has built an optimized hardware-audio engine to perform the decompression. According to Roberto Simmarano, the company’s senior marketing director for the communications-business unit, when you move from a lossy codec to a lossless one, 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, such as MP3, WMA (Windows Media Audio), and AAC (Advanced Audio Coding), for the least amount of power consumption with zero CPU load. The audio postprocessor implements an ASRC (asynchronous-sample-rate converter) with near-transparent quality. The processor achieves a range of 136 dB using a multipass algorithm, a multichannel mixer with limiting function, and a 10-band graphic equalizer. Three sets of I²S outputs can independently control stereo speakers, the associated subwoofer, and headphone or line outputs or can act as multichannel audio outputs. A 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 subsystem. In this scenario, the IC provides direct support for a variety of removable and embedded flash-memory types. AMS supplies the chip in a 66-mm CTBGA package. Simmarano declines 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.