Introduction

MP3, AAC, iPods, digital radio, digital TV, Surround Sound, 5.1, 7.1, Ambisonics, stereo, multichannel and others have been familiar terminologies to our ears, and close technologies to our hands.

Since the memorial times of Gramophones till the current iPods, the audio technologies had been undergoing a continuous and natural evolution in its whole chain of production, distribution, and final
presentation for listening. The electronic and digital technologies are basic bricks for building recorders, processors, synthesizers and players, and we see that new projects and next generations of sound systems come to satisfy the human demands, not the tools limits.

In the popular domain, the stereo format still reigns. However, the consume of multichannel audio, still a new culture, is now more popular thanks to the facilities of digital technologies. Sound players
revolution continues with the personal solid-state devices, based on electronic flash memories, without mechanical components. The cinema, for instance, in two decades improved much more in the sound presentation than in the video presentation. So, where are we going to?

Naturally on the evolution course of the musical and sonic sciences, trends satisfy a clear demand for a more realistic audio presentation, in high resolution and high quality. Some general trends can be pointed out:

· the active participation of the listener (user), not only in the reproduction control, doing his/her own choices at any given time, but also in the sound scene control, something closer to a producer's touch

· the capability to spatially locate individual sounds around

· the capability to edit and recreate a sound, following personal tastes

· the augmented capability to choose programme, to detach one instrument, to select the language...

· the capability to alter the musical piece, creating something new at reproduction

· the power of immersion, to be in the middle of a sound field, creating or reproducing virtual sound environments, synthesizing a sonic world

· the feature to equalize not only bass/treble or frequency bands, but to equalize the acoustic scene, the physical environment, and even to correct local acoustics for better

· the capability to store thousands songs in tiny mobile devices, of easy access (even wireless...)

· the capability to produce sound volume with high performance and low power consume

· the augmented sound illusion...