In stereo music, the sameness in the difference between the loudspeakers ‘opens up a “virtual space” between them’.
This ‘virtual space’ is a phase space replication of the original space of sound recording.
Stereo music not only provides a playback of the music that was recorded, but also of the space around it.
This is the basis for the recording of ‘silent music’; replication of the (dynamic) space ‘only’.

“Stereo” is the equivalent of a hologram.
Due to its temporal organisation (replication), a hologram has seeming persistence.
Due to its temporal organisation, stereo sound image has seeming transience.
Yet, understanding that replication =~= invariance, both can be regarded/experienced as ‘same’.

Experiments have been done with sound projections; “sound scapes”.
Therein 3D positioned loudspeaker were used to selectively amplify/suppress sound.
This makes use of the standard principles of wave interference; the core model of “sound”.
Therein the space phase of a region in space is superimposed on the phase space region of sound.

This is the well known principle which is used in Stereo Music recording.
The sound of the orchestra is recorded, including is spatial distribution.
When replayed, the position of the instruments can be recognised in the acoustic image.
It means that in stereo recording, one spatial domain is superimposed on another.

In this recording, not only the sound is represented in playback, but also the space around it.
In that manner the cathedral of an orchestral recording is superposed on the room in which the music is played.
Some amplifier systems offer as a standard feature that this ‘space’ can be modified’ to ‘different sizes’.
By using phase delays (‘echo’) the virtual space can be expanded and contracted.

• This has been used in city-scapes, for defined sound projections.
  Music is then audible on a terrace, but not beyond it.
• This is being used in car engines, for sound suppression.
  Engine sound is played back, inverted, ‘cancelling’ the sound of the engine.

The space phase information is the core of the idea of MatheMusics.
What is implied in “stereo” is explicit (phase space) is explicit in MatheMusics.
Music is a format/language/means by which we can confer/communicate this phase space.
Music is a means to be able to sense what mathematics tries to describe.