what does "Air or a Halo around instruments" mean?

Tubegroover, I quite agree with your point, but found it difficult to differentiate the halo-effect from what is described as natural decay, since the halo will decay together with the tone per se. In a live offering, easily to hear with chamber music in a smallish hall, or with a solo instrument played in an ordinary room, you can easily discern the halo forming around a note played, which can be quite startling, if you've listened to canned music for a long time, because I know of no system, which is able to reproduce this effect properly. It is either missing entirely, or truncated, or as you so rightly suggest, simply too slow. Live certainly is faster, I agree, also more compact as a cluster around the central tone.

Last Saturday I went to the symphony. I heard Beethoven.
I did not hear any air around any of the instruments in the orchestra, nor around the piano playing the piano concerto.
And 3 weeks ago I went to a 3 day folk music festival with all music played through a concert sound system, even the classical guitarists. I never heard any air around instruments there either.
What I did hear at both the Beethoven concert and the folk music festival was music that had a wholeness to it. The symphony was as one instrument with many many individual colors. And music through a sound system is completely as one, no matter where on the stage the person is playing.
I have often read the phrase "air around instruments" in reviews. But is this not just one of those "audiophile sound characteristics" rather than what music really sounds like?!

As with Sharri, I do not hear air around the instruments. After reading numerous posts on this subject I was ready to do a system change for this very reason. I have a soundstage and the speakers disappear, but would have a difficult time telling where a musician is on stage unless playing a solo, especially with a full orchestra piece. I can generally sense where the musicians are with small groups as in rock or jazz. I have recently been attending many concerts which featured jazz as well as classical music and noted exaclty as stated above, that in general the music comes to me as a cohesive whole.

Well, I suppose it is a function of hearing acuity, perhaps also a question of having absolute pitch or not. I don't know. I listened to a lonely flute player in a Zurich park yesterday and the way his tones formed and carried had plenty of air. Afterwards I went home and listened to solo flute music, similar to what was played outside on this beautiful spring day and at least a third of the air was gone. "Air" is what lets the music spread in space and our stereos certainly have (indeed sometimes shockingly!) less of it. Especially as far as orchestral music on CDs, without upsampling are concerned.
I agree partly with Jetter, that you can listen to a musical interpretation as a cohesive whole. But then, I suppose its training, you can easily focus on a single, or a group of instruments, even in big orchestral music. What do you suppose conductors do, when in rehersals they form the sound of a given orchestra according to their ideas of interpretation? Even during a tutti, they have to differentiate their hearing to grasp what the horns, the celli, the woodwinds etc are doing and this goes down even to single players of whatever section. Cheers,

Moving air is what music is!
Most music reproduction systems tend to lose much of the "moving air" that is the music. The dynamics and clarity of live music just vanish. Ever listen to your system after coming home from the symphony??!! Does it sound like you are sitting in the foyer, or on the main concert floor?
A system that has "air around instruments" may have a bit of the dynamics and details of the live experience. And perhaps that's what this refers to.
But at a concert, I never hear "air around instruments" but I do hear a lot of moving air. To me, it seems like that is a difference. But maybe not.
BTW, I do not have perfect pitch or hearing.