Well, a band or performer who has done a thousand shows, it could be "just" memory.  About a million bands and performers on any given night are out there doing shows in clubs and etc, and pretty much none of them have a music stand up there.  Most of them or at least a good % of them have standard music training so far as I've ever known.  Some may be playing "purely by ear", but for most it is memorization and being aware of the music and taking cues from other performers and other things you learn in rehearsal.

I don't know if I "truly play by ear" in the sense Oliver means it.  But that's what teachers and music profs called it.  Some teachers considered it a very bad thing, enough so that I kind of avoided music lessons and etc for years.  So while it is useful in practical playing situations, I've never thought of it as particularly being a "plus".  I can't do it equally well on all instruments, if I want to play an instrument by ear, I have to learn it and practice it that way.  If I learn an instrument from written notes, I play differently on it because I will unconsciously follow certain rules and theory that are sort of linked to the standard notation staff for me.  It is just how my brain is wired.  To "get over" that, I have to play the instrument a lot, it is a bit difficult for me, and as such I haven't ever gotten around to doing it successfully with keyboard/piano. 

For me, at least, how "playing by ear" works is that if I am sufficiently fluent on the instrument, I can play pretty much any melody or bit I have heard or thought of.  What I call "being fluent" is the ability to take any note you hear or think of and just play it without having to think at all about what it is called or what string or finger.  Your hands know where it is and it is as natural as singing or whistling.  Very little (if any) hunt and peck.  Where it will still take some "working out" is deciding on the finger moves and voicings, style and expression moves like whether it might be better to slide up to or down to the note instead of just hitting it directly.  To get that on an instrument, I have to play a lot and in different circumstances, so it becomes like having another voice to sing with.  That is what I am trying to do with violin, my main goal at this time for violin/fiddle.  I am still a good ways off from that goal, so there is certain amount of hunt and peck to work out how to actually play a melody or phrase, but with each one it gets a tiny bit easier and I feel more "at home" on the instrument.  It is a very particular discipline and it takes a certain amount of work to be able to do it well on a particular instrument.

Conversely, playing from written score is a different application/discipline.  It is worthwhile and respectable, but it is not my goal at this time, other than a bare minimum so I can work out a piece from score if I want or need to.  But for what I am trying to do, at this point playing from score is "cheating" for me, because it does not help get me to the goal I set.  So I avoid it mostly other than some basic scales and allowing myself the occasional "cheat" if I see a bit of score that looks interesting and I want to hear what the person who set it down did with that melody or idea.  I do not see myself playing the instrument in a recital or symphony setting, where I feel that sight reading would be more of a requirement, so it is not a priority goal for me personally at this time to work on sight reading skills for violin/fiddle.

Anyway, whether or not what I do it "truly playing by ear" as Oliver means, I am not sure.  While some of it is a natural thing I have always been able to do, it does take a certain amount of work to be able to do it on any particular instrument.  Is a thing more true if one is entirely born with it than if one works to have it?  If two individuals are "wealthy" and one was born with it and the other worked to get there, is the one born with it more truly wealthy?  I don't know, that is too big a philosophical question for me.  I'd personally say that it probably spends the same either way.  LOL

Sure, teachers and profs called that particular ability "playing by ear" but they can be wrong sometimes too.  The head of the local college music department always claimed I have "perfect pitch", but I do not.  I have a pretty good relative pitch, which is actually a different thing.  My relative pitch is just maybe a bit better than his, so he thinks of it as being perfect pitch. 

I don't worry much about it.  But I play and compose very differently on instruments I learn mostly by ear than I do on ones that I learn by learning to sight-read for, so I sort of have to pick one or the other at least as the main mode/priority.  For violin/fiddle and what I can think of myself maybe doing with it in my life, I want it to learn to play it by ear and so that is what most of my work is towards.

Thank you, MGN.  I enjoy your posts as well.  I played in bands for most of my life, so your talk of gigs and your obvious "fire" for music are just great to see. 

Oliver:  Ok, I saw your post in another thread and it had an opportunity for me to maybe show you what I mean by "playing by ear".  I would agree that version of "Turkey in the Straw", well you just don't get much better than that.  And you probably won't ever want to get much worse than the one you will be able to hear in this example.  I stopped the vid right after he had played the piece through.  I made it a point to just listen, not watch how he was playing the song.  No score, and I have never attempted "Turkey in the Straw" on violin/fiddle.  I have played it on guitar in a couple of impromptu jam sessions maybe 20-25 yrs ago, but haven't played it on any instrument since.  So I'll call it close enough to "a fresh piece" for me. 

I picked up the instrument, checked my tuning, and turned on the evil unforgiving recording software.  This is a take nobody but *nobody* would normally ever get to hear from me.  My first attempt to run through a melody/song.  Nothing written to go from, didn't watch the guy's hands, I'm just going on sound.  Uhh.. If cats or dogs are present when you play this, you may wish to be a kindly sort and cover their ears.  Plenty of squeaks and etc, since I'm just trying to get the notes of the melody, and I'm not good enough yet to get them sounding *good* without some practices.  Listen at your own risk, you have been warned. LOL  Didn't even bother with noise reduction,  eq or reverb, so it's pretty "raw".

I think that at least some of it is learned, or gets better with use, Oliver.  I would like to say that I think it is something everyone has and it just takes learning/practice.. But I can't, because I have known and played with musicians who could not work something out for themselves by any means at all.  I've also known some who couldn't tell if they were in tune.  I'm not talking off by a little, I mean where they'd tune a string like 10 or 15 cycles per second flat and obviously not be able to tell. 

So far as retention, if I work a piece of music enough to build up some '"muscle memory" where my fingers know it without having to consult with my head, I can get rusty on it if I don't play it in a long time, but it will come back to me fairly quick.  As I've mentioned in other threads, I think it is always quicker to get something back than to learn it from zero in the first place.

If you mean the other sort of retention/memory, yeah, I have Ian  Walsh's version of Turkey in the Straw in my head now.  It isn't the first thing I've heard by him, though, like your version of "Rainbow Connection" or NV's "Ode to Joy" or FM's "Pop Goes the Weasel".  First thing I ever heard by Ian Walsh was his "Old Joe Clark".  Some people remember faces or names, I remember a musician's "sound".  And usually the first piece I ever heard by them as well as other pieces that were particularly memorable.  Kind of like seeing pictures of a person over time in different circumstances, you sort of learn what they look like.  I remember bits of music, not quite "eidetic" but related to that sort of thing.

Before that is something anyone wishes they had, notice all the ridiculous commercial jingles and bad muzak and etc you hear in a day, and be glad if you can forget at least most of it. LOL

Now about that guy who knew a "hunnert" songs by ear, Oliver..  Maybe we could get him into a band somewhere with a few musicians I have met over the years who bought a cheap "fake book" somewhere and no matter how hideously off the versions in the book were, they absolutely insisted they had to be right because "It's right there in the book, man.."  Yeah, like written scores never have typos and are never made up by people who have composing and transcription/transpositions skills that are.. shall we say a bit dubious?  LOL  So tell you what.. Let's get that guy together with those people, and have them form a band and then we know one show that we definitely will want to avoid seeing. LOL

But back to sheet music being evil.  I don't feel it is.  It can a good tool for what it can do, and useful for some things.  It is not automatically good either, though.  It all depends on what you are doing and what you want musically.