The MDI Multi Dimensional Imaging, is a 3-D Sound Enhancing algorithm that widens stereo soundstage and creates a 3-D sound field using only 2 sets of loudspeakers.
Our perception of sound sources placed in 3-D in space in near field is determined by the differences in audio information picked up by our left and right ears and neural analysis of this information. The subtle differences are called cues and are of 3 types:
1. The first is the ILD or Inter Level Differences in our ears caused by the shadowing (i.e., the very presence) of the head.
2. The second is the ITD or Inter-aural Time Differences between the two ears caused by the not only physical separation between the ears but also the fact that sound takes different times to travel from the source to the two ears.
3. The third which gives the spectral cues is more complex and depends upon the frequency response of the ear to sound waves arriving at different angles to the eardrum caused by interaction of the sound source with the head, the torso and the eardrum.
Through clever signal processing of the stereo information from the stereo soundtrack differently for the two channels, in phase and frequency, it is possible to lead the ear into believing in the existance of sound sources beyond the stereo sound field and thus creating an illusion of 3-D sound field.
The MDI developed by Sonodyne evolved from this concept. It started with theoretical calculations and circuit implementation and was fine-tuned through countless man hours spent in listening. The end result is a previously unheard experience in room filling 3-D sound.