I don't see this as being complicated at all. I think this is a case where we should "think inside the box" rather than concoct a complication which does not exist.
Ron, I agree it is not complicated. I do not really understand what you mean by "think inside the box". I am not trying to "concoct a complication". I am describing what I hear when listening to both live music and to different stereos. I see two different ways to interpret this phrase, in sonic terms and in visual terms. That leads to confusion, and I am interested in more clarity when it comes to describing what we hear to others.
This is separation of instruments. You notice "such sound" separate from the tubas and tympani on the opposite side of the stage.
I notice distinction between the sounds of instruments based on their different timbres, volumes, and the timing of when the sound was created. Is this what you mean by "separation of instruments"? I refer to this as a sense of clarity and lack of homogenization. You describe the location of the piano or bass.
Why would there ever be a "lasting [sonic] image" of a transitory event? If you're walking on the street and you hear a car backfire, your head swivels to the source of the sound. Why would there be a lasting sound of a car backfiring after its momentary backfire?
I am not suggesting there would or should be a lasting sonic image of a sudden burst of sound. The sound radiates outward. The instrument remains stationary. The only thing lasting is the remnants of the sound filling the hall, and it does not last very long.
Why would there be a "lasting image" of a drum whack?
When I listen on my stereo to a recording of a three-piece jazz band, and I have a sense of the bass guitar player in the middle, and the piano player on the right side, and the drum kit on the left side, I am hearing "separation of instruments."
"Separation of instruments" is not the problematic "clearly delineated sonic images" which I agree with you are hi-fi artifacts which I do not hear in real life in the concert hall.
Yes, I hear that too from a three piece jazz band. General locations of instruments can be heard. You do not need a great stereo for that. I hear in from my car radio and I hear it from basically every stereo system and in the jazz club. Is that really what we are describing with the phrase, "separation of instruments"? Why not just say "I hear the piano in the middle between the double bass and the drums"?Do we need a different way to describe that?
The phrase seems to be used as a positive attribute which improves as one improves his system or upgrades a component. How exactly does it improve? What gets better? I can understand how this phrase describes a sonic distinction between timbres, volumes, and timing - the distinction between the sound of the individual instruments and the rest of the orchestra, as Tim described.
I have trouble understanding why the phrase is used to describe improvements in the visual sense of "clearly delineated sonic images". These are what I heard in that system where the instruments were isolated and separated from the rest on stage. As a sonic quality I understand it , as a visual quality as in the physical separation of instruments, it does not seem necessary, unless one is describing ever increasingly delineated images. This is what I do not hear from live music, nor from natural sounding systems.