In the previous post, I described how the use of fading volume could break the suspension of disbelief of a spatial audio image, because it is physically unrealistic. Now I am going invert the argument.

Space is implicit in perceived sound. You cannot perceive a sound independently of a space. As Blauert says “Spatial hearing is a tautology”.

Schaeffer’s concept of source-cause articulated that our perceptual systems will first and foremost attempt to identify the object making the sound. The point I’d like to make is that since space is implicit in perceived sound then our ability to identify the sounding object must include an ability to ‘parse out’ the spatial information within in the sound. The sound of footsteps is still recognisable as the sound of footsteps irrespective of the hosting space.

An other way to state this is to say that we have an ability to identify the space described by sound, irrespective of what sound is inside it.

Further to that; the spatial information in sound is maintained when sound is reduced to singular audio channels. A mono recording of a choir singing in a church will still communicate the large reverberant space.

… and so when an orchestral work uses a long slow volume fade, our perceptual system will attempt to read the space implicit in the sound. If the orchestration is done right one possible spatial interpretation is that the volume fade infers sounds moving away from the listener. In other words, the impression of a movement in space is created.

I’ll go one step further and postulate that when composers fade the volume of sound, what is being inferred (the majority of the time) is a movement in space, away from the listener.

Composers are far more accustomed to the communication of spatial information at this level. Whether it be movement through volume fades, large spaces through reverberation, or even panning it is not necessary to create a virtual-reality to infer space.

But what happens if a space is inferred using these non-virtual means and a space is modelled using virtual means?