Design Article
How audio products will impact your future
Kenneth Boyce, National Semiconductor
3/15/2006 9:24 AM EST
Digital Signal Processors (DSPs)
Digital signal processors have evolved into powerful, cost-effective tools for audio processing, greatly enhancing consumer audio products. Future DSP capabilities permit even more multi-channel, calculation-intensive audio processing algorithms. In combination with microphone and speaker arrays, these increasingly intensive algorithms will automatically match the listening environment or alter its acoustics.
Large rooms with poor acoustics can be made to sound like a majestic theater. A small living room becomes an intimate home theater wrapped in comfortable, distortion-less sound that won’t annoy your neighbor. Or, you may listen privately with headphones and still get the "big theater" experience. Just select the audio environment and either speakers or headphones, and the DSP algorithms adjust the audio playback accordingly. For commercial use, systems will automatically adjust to room size changes (done with movable dividers, for example).
In the near future, DSPs will allow a broad array of automatic adjustments for background noise, echoes, and feedback, and physical speaker/transducer anomalies. Alterable sound environments will enhance computer games, music systems and video entertainment systems. With powerful DSP processing, there will be a single flat-panel multiple speaker array that replaces traditional front, rear and subwoofer speakers, eliminating several boxes and most cabling.
Audio Coding and Decoding
The MP3 format is probably the most popular digital audio encoding and playback format. Other audio coders (MP3Pro, AAC, ePAC, AC-3, Ogg-Vorbis, WMA) use similar perceptual sub-band technology. These have varying degrees of improvements in data compression ratios and audio quality over MP3, but require faster processors and more complex encoding.
File size compression ratios of 12:1 to 24:1 for Compact Disc and FM radio "quality" are now commonplace in many coders. Users compare the "quality" of these coders/decoders to that of audio CDs. Perceptual coder makers define "Compact Disc quality" to mean "listener indistinguishable from Compact Disc audio".
SA (Structured Audio) is essentially MIDI combined with compressed digital audio and commands using Structured Audio Score Language (SASL). The SA Orchestra synthesis engine can be used to play most, if not all, instrument sounds. Vocal content is compressed separately and then synchronized on playback with the synthetic orchestra to "play" the song.
Since most of the sound data is synthetic (instructions to the SA Orchestra similar to MIDI files), SA file size and the compression ratios approach 100:1. Since the song is re-mixed by the playback device, the device could also choose an optimal mix for the listening environment, such as 5.1 Dolby Digital or DTS for home, a headphone mix for private listening or a 4-channel mix for automobiles.



