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

Ive heard many reviews describe speakers that have "Air or a Halo around instruments" , what exactly does that mean?
I hope this helps a bit... I liken it to the halo effect one sees around a street light late night with a bit if humidity in the air. The sound around instruments is somewhat the same, occupying its own space that black velvet contract of space or background(quiet background)is what makes this effect possible. This effect allows
the sound to bloom like a ripple in a pond until the sound wave has completed its course. It isn't a predominate effect but one which depending upon certain musical arrangements or style of music which can add an element of emotion which draws one into the music at which point you are no longer a spectator but a participant.
Thats my take on it and I feel tube equiptment is the best at delivering this type of sound, if done correctly.
Good luck and continue searching for that sound its out there.
PS. This effect is the result of the sum total and NOT any one piece of equipment, but consider cabling as an important element of this synergy as well.
It means the instruments have their own distinct space, with a buffer (of air) between other instruments. It generally implies a 3 dimensionality sound of the instrument or group of instrument--where each has it's own distinct place in the soundstage. Planers and electostatics generally perform this "air" very well, where as horn speakers (in general--not all) do not.
Eantala, there is a difference between "air" and "halo". when i owned Wilson Watt/puppy 3/2s and then later 5.1s there was a definite "halo" of energy around images that i became enamored with. this "halo" would slightly highlight and blur images.....but at the time i liked it. my opinion is that it was an artifact and not natural. when i upgraded to the WP6 the "halo" went away....and at first i thought i was missing something. then i realized that on the WP6 images were much more 3-dimentional and organic. and that i was getting ambient clues previously obscured by the "halo".

"air" can mean a few different things; it can mean a sense of real space that the instrument occupies.....it can mean the "presence" of the room and resolution of the total space....it can mean the high-frequency extension and floating sensation of notes as they decay. obviously, these meanings are related but slightly different. another way to put it would be to say that "air" and "open" are similar.

"air" sounds natural....."halo" is an artifact of the reproduction chain. you will never hear a "halo" in a live performance (based on my interpretation of that word).
Abstract7 is right to my mind. If you listen for example to a solo violin or a solo piano very carefully, you will notice, how the tone appears and spreads in the soundspace with its overtones forming a cluster around its tonal core, if you like. If you were to translate this into colour, it would, for example be like a strong red at its central core, which then would spread out, like ripples from a stone thrown into a pond, into different hues of red, getting weaker and weaker in intensity. It is how the tone, or a succession of tones, spead and decay after their first appearance, which is called the halo. If a system reproduces this well, it has , as Abstract has suggested, air. Electrostatics do this quite nicely, though still far from the real thing.
I've found that cables (matched to the system) are really what makes or breaks this effect. I can put a badly matched cable into my system, and instantly it is transformed from 3d to 2d.

Tube equipment is definitely the way to go for a sense of presence or air. You can get a 3d effect from solid state, it just doesn't feel as 'alive'.

When a system is well set up, you can distinctly tell that there are x players in the room, and where each one is sitting & how far apart hey are. You can also tell when one moves their instrument up or down. You can almost feel like you could get up and walk around & behind each individual player.
I don't have the vocabulary to articulate the concept fully, but I will make a suggestion that may be helpful. When we attend a live performance our visual cues often overcome our sonic attentiveness. Try closing your eyes as you lisen to live music and allow yourself to get a "sonic image" of the instruments or voices. Also note the quality of the sound, timbre and pitch, as the instruments (voices) interact with the environment. I have found that using this kind of reference allows me to judge the veracity of an audio system. I agree with the above posts that in my experience tube amplifiers and pre-amps are better able to achieve this sense of dimensionality and space.
Air is the space around individual instruments. When you hear halos I would guess that you are exciting the angels :)

Detlof your explanation is interesting however I always referred to this effect as the natural decay. Sometimes when I listen to this effect and I certainly hear it in spades on some recordings, it appears the decay may be a bit longer than I note with live music as though there is some type of reverberant effect added to the recording. Even a reverberant hall doesn't seem to hang on to notes as long as certain recordings do. At least I can't recall hearing it to the same degree. Live seems a bit faster.
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.
Eantala, I interpret air to mean hearing the ambiance or environment into which the instrument is playing. For instance, you hear the oboe soloist not just playing notes to the left of center orchestra (localizing within the soundstage) but also projecting sound into the acoustic of the concert hall. You hear the sound of the instrument and the dispersal of the sound at the same time. I used to think this was just exageration or poetic nonsense. With a tube amp I finally heard and understood what they were talking about. It's one of those things you have to experience yourself to "get it". I never really heard it with solid state so never knew what I was missing.
I think "air around instruments" is sort of a mixed metaphor, if you will, so we end up talking about two different things here. Having a system reproduce voices clearly separated in space is a soundstaging feature, and one, IMO, that is not terribly realistic, as others have noted. Still, I'd rather have it than not. Soundstaging "tricks" are often very pleasurable surrogates for the natural spaciousness and grandeur (not to mention the visual aspect) of live music that most of us cannot hope to reproduce in our homes. I'm willing to be duped by good soundstaging.
Air, it seems to me, is not a soundstaging feature. It has to do with fine detail that captures the interior texture of sounds. I think I'm with Sharri here. A system that does "air" well conveys the sense that music is aural painting of air, that the sounds are illumined and alive on the inside. It's easier to think of what lack of "air" is: a lot of reproduced music gives dynamics, shape and surface texture to the sound, but ultimately the sounds are rather dense and inert on the inside. My four-bit words on the subject.