Is there any such thing as reducing the volume?
Its not a trick question. If there’s a truck across the road, I can’t reduce its volume.
When the truck drives away, its volume will fade with distance. If I close my front door the sound will be occluded (blocked) and it will be less loud. If I walk across the street and ask the driver to turn off his engine it will stop abruptly, clunk-out.
But its loudness will never fade away in the same manner as if I turned a knob on my amplifier.
In reality, when a sound’s loudness drops, lots of other things will always happen to the sound. For example, when the truck drives down the road its spectral character will also change. The humidity in the air will cause its high frequencies to be increasingly attenuated as it moves away. And the myriad of first reflections will change as the position of the truck changes relative to hard surfaces like walls. Not to mention the change in sound of the engine as it accelerates!
So when a spatial audio composition contains a sound which is faded away in volume, what happens?
To my ears, the believability and immersion is destroyed. Its like throwing a hammer into a mirror. The image disappears. Reducing the volume is a spectro-morphology (to use a Denis Smalley term) which can never occur in the real world. It is fictitious. We have no experiential memory of any sounding object in space that can behave as such. Unless, ofcourse, the truck noise across the road was actually made by an audio speaker (in other words it was faked to start with).
In the virtual reality (VR) world, where researchers are concerned with creating a sense of presence (auditory or otherwise), this might be explained through the concept of scene-consistency. If the sound of the truck is reduced in volume without respect to the existing space, then this would create an inconsistency in the scene which would compromise the suspension of disbelief.
In the next blog post, I am going to invert my argument.