I am not a music expert and I have always wondered why orchestra performances require a conductor to play. The musicians are presumably professionals who have had much practice at this point, so why do they still need direction? Other musical groups such as bands or soloists don't need any extra guidance.
And on a similar note, I also tend to see orchestras with sheet music in front of them. For the same reasons, why is that?
There are several reason. The most basic would be “so that they could play together”. A symphonic orchestra is much bigger than a band, and being in perfect sync with the player at the other side of the stage or pit can be hard without visual cues. In smaller ensemble, such as a quartet, quintet, or even chamber orchestra, there might be no conductor or the conductor might be a musician among others.
The second, most important, point is that the conductor actually, well, conducts the piece. They decide of how the piece is to be played, at which tempo, with which atmosphere, … They are the master of everything unwritten on the sheet. Heck, they also are the master of everything actually written on the sheet if they deem so necessary. This information is conveyed beforehand, during rehearsal, but also during play; a good conductor will convey a lot of information through body language. Have you ever seen a (very beginner) conductor who doesn’t breathe when should? It’s awfully hard to understand even when to start playing. And that’s for the basics: when to start, etc. A good conductor will express which emotions they want the music to convey through body language.
As for sheet music, that would depend a lot about how the music is written. Most orchestral music is quite structurally complex with respect to pop music standards. A pop song usually is a chorus, a few verses and a bridge or two intertwined. What you need to remember is the chords, themes and your part in each of these section, and then you’re good. You can move around those a bit to make the music richer, but that’s it.
In an orchestra, however, the pieces can be much longer, the parts more complex or, well, boring (“count 76 measures”, anyone?). Orchestras also typically have a wide repertoire, and little time to rehearse each piece in that repertoire. You could very well have only one or two rehearsals before playing a piece. Sure, each musician works by themself, but that’s little help.
On the other hand, soloists spend more time studying and practising a piece, and, as soloists, play mostly themes which are easily distinguished when listening to the whole piece, which explains why they can often play without sheets.
Let me try to add to the excellent answers. In general:
Your question is legit, but it can be readily explained with scale.
Compare: "me and my brother built a doghouse yesterday - why building a skyscraper needs an architect and blueprints?" :)
More in detail:
The musicians are presumably professionals who have had much practice at this point, so why do they still need direction?
Rocket scientists can have a chief - often more senior, more experienced - scientist as well, coordinating the effort and giving general directions.
The conductor does the same, but since the score is often open to some degree of interpretation he also disambiguates and, one could say, imposes a unique vision, going so far as doing slight edits to the score.
This tends to work better than 90 musicians in a hall arguing about how fast "presto" exactly is.
So, the conductor's job is mostly done in rehearsal.
During performance, he provides visual cues which might be helpful for playing in perfect sync (although this responsibility is often shared with e.g. the concertmaster).
Other musical groups such as bands or soloists don't need any extra guidance.
This is a bit of a false analogy.
At the extreme, a 4-element crust punk band playing in a club full of drunk people doesn't require guidance in the first place, because the music is less complex, everybody plays on 11 anyway and disputes can be conveniently resolved by physical fighting :)
As for the tempi, that's what the drummer is for, keeping the beat. During the quiet passages, you may sometimes notice the drummer is keeping the time aloud with his sticks anyway, in fact doing what the conductor can do purely visually with his baton.
Speaking of visual cues, notice how at the beginning of this video the drummer counts out the time, keeps the beat with his hi-hat and... notice what happens at 4:35! :) http://youtube.com/watch?v=mQZmCJUSC6g
Note that big bands do often have a conductor or a leader, anyway.
The function of the conductor can be better understood in an historical perspective, if you want. The figure of the conductor (as opposed to the concertmaster, an instrumentalist which covered some of the above functions) emerged in the 19th century, when music became more complex, a greater variety in tempi and dynamics emerged and orchestras grew bigger.
Modern-day smaller chamber ensembles can still do without a conductor for the same reasons (and historically informed performers may chose to do so even with larger ensembles/works).
And on a similar note, I also tend to see orchestras with sheet music in front of them. For the same reasons, why is that?
This question can be rephrased as "why was writing invented"?
Of course, because it is more practical than committing everything to memory if you don't have to :) - especially when performing complex, non-repetitive, lengthy pieces of music with dozens of other instrumentalists where you are kind of required to follow your part exactly for the whole performance to work (whereas in a 4-piece rock band the drummer might change a fill and nobody would care much).
In orchestral music, tempo often varies a lot, and it's much harder for a large group of players to speed up / slow down together than it is for them to just keep going at the same speed, so a single source of 'pulse' is useful here. Édouard mentioned the size of the orchestra making it hard to hear - one reason is that an orchestra pit can be 20 metres or so across. Sound takes more than a twentieth of a second to travel that distance, which may not seem a lot, but does make it very hard to play in time from the audience's perspective, which is another thing that the conductor represents (it may be hard for a single instrumentalist to judge exactly how loud they should be playing - a conductor has a better perspective here).
Realising an orchestral piece is a matter of interpretation - there's often not enough information on the score to make the piece sound good musically, so it's up to the conductor to give sections detailed direction about volume, playing technique, and rhythmic feel. A lot of this work will have been done in rehearsal.
Also remember that not all orchestras are made up of flawlessly-talented musicians - there are amateur and youth orchestras who may have members who need some help; and when you've been counting 50 bars to wait to do one cymbal crash, a gesture from the conductor showing that it's the right time can be very reassuring!
Part of a night at a concert is the aspect of putting on a performance, and a conductor is an expected part of the show; he will be a focus of the audience's appreciation; introduce pieces to the audience; greet soloists; tell the players when to stand to take applause, and so on. In many ways it's their night, and the whole feel of the show would be very different without them.
As for the sheet music : in an orchestral performance, a player may well be playing a piece that they've not played before and have limited time for rehearsal - the particular part may also be musically 'non-obvious' in isolation, only making sense when combined with the other parts, so harder to remember. Not to mention that pieces are often very long and don't have as much repetition as your typical rock song.
Soloists, on the other hand, will often be expected to perform without music - they'll be expected to be better-prepared, and also their part will be easier to remember as it is the melodic focus of the piece.
A conductor provides different things at different levels of musician skill.
At the lowest level of skill, they keeps time and tempo for you.
As you learn to keep your own time and tempo, they begins to provide dynamics.
As you learn dynamics, they provides key cues. It is not uncommon to have a long pause followed by a sharp note in many instruments at once. Doing this without a conductor coordinating is tricky.
As you get good enough to work together and hit the timings, a conductor really begins to bloom. Just when you thought it should be an unimportant role, it becomes more important. The conductor starts to provide a central sense of emotion. It's one thing to hear an orchestra play a song sadly, with 50 individuals playing their own version of sad. It's an entirely different thing to hear an orchestra of 50 individuals playing the same version of sad.
Eventually you get better at doing emotion in unison. Now the conductor starts to become your best friend. You have the skill to organize without a conductor, but a conductor can take care of things you don't want to. If you've got a conductor playing the complicated dynamics of emotion and feel at the orchestra level, you can concentrate on playing your instrument to the best of your ability, knowing there is a conductor to hold you together. You're a musician. Spend your attention on your instrument.
Finally, at the epitome of skill, the conductor becomes a peer and a trusted friend. At some point, you can't go any further without losing yourself in the music. Someone is going to have to find you again. That person is the conductor. I will never forget a beautiful violin concerto done by a brilliantly talented violinist. She started the concerto with her opinion of what the music should sound like in one of the classic opening concerto solos. The conductor smiled patiently, and let her take control of the music completely (he even adjusted the tempo to suit her). As she continued the ferocious stream of notes, you could see her start to destabilize -- the music literally was taking control of her. The tempo wavered just a little, suggesting ruin.
Then, in one moment, the conductor changed how he was conducting ever so slightly and locked her playing into something he had some control over. He then tied her emotions directly into the orchestra, so she was no longer just a soloist, but part of the orchestra.
Once she was assimilated, he pushed her harder. He drove her further into the emotion and speed until I don't think she could have stopped if she had tried -- her fingers would have unraveled before she could have stopped the violin from playing its notes.
Half way through the final movement, he calmed things down and let her lose. She finished off the concerto in her style, under her own power. The applause at the end was deafening. She proudly took a bow for her skilled work, but you could see from how she shook while bowing that the conductor had taken her to a level of skill she wasn't even aware she had, let her grasp the stars, and then come back safely.
That, my friend, is what you have a conductor for.
Conductors are not actually required; there is a long history of conductorless orchestras.
However, having a conductor is certainly useful for the reasons stated in the other answers. It's also worth noting that the conductor often has a leadership and training role in the orchestra -- so it's a bit like asking "why does a basketball team need a coach?"
As for sheet music, it's not required either. Soloists playing with an orchestra typically memorize their parts. But again, as in the other answers, sheet music is very practical, especially for the accompanying instruments who may not have any memorable melodies at all and yet have to count out long rests of seemingly random duration.
Lots of the points have already been made, but regarding the need for the score I'll give an example which illustrates the point. I play in a guitar orchestra of 25 - in our last rehearsal our conductor added no less than 16 new instructions to the score for a piece that is only a few minutes long - including what tone to play (dolce, ponticello, pizzicato,staccato, vibrato, open or closed strings, rest stroke or free stroke), how fast to play and when to speed up and slow down, how loud to play and when to get louder and softer, the relative loudness of different guitar parts at different times, which notes require emphasis, etc. So at the end it sounds nothing like it did when we ran through it without him beforehand (thank goodness!). So the reason for the score is not only so you don't have to memorize your part when you may not have the melody and have rests of varied length (8 measures anyone?) and have to come in on time, it's also so you can follow these extra instructions for your part.
A conductor is especially needed when there is a large group of musicians and the music being performed is such that the tempo is constantly changing -- gradually speeding up, slowing down, or radically changing speeds suddenly. And it is the conductor's job to choose how much to speed up or slow down, and when. The same goes for the dynamics -- how loud or soft, how gently or forcefully, each section of instruments performs at any given instant. The conductor controls this. Thus, different performances of the same piece of music by different orchestras led by different conductors can, and should, sound quite different, if you know what to listen for.
The conductor has his or her own ideas about how to interpret things like tempo and dynamics, and the subtleties of rhythms, at each and every point in the score. In rehearsal, the conductor teaches the orchestra to play the piece (which somebody else has already written and notated on sheet music) the way that the conductor wants it to be played. Then, in performance, the conductor uses his or her power to interpret these things. The members of the orchestra are required to follow along and do what the conductor is instructing them to do at each instant.
A small band that plays a piece of pop music that has the same unchanging, steady tempo and rhythm all the way through, and not much dynamic variation, has less need of a conductor. The musicians can listen to each other and figure out what to do at each moment.
Small classical music ensembles (who play music that does have lots of rhythmic, tempo and dynamic variations) can do without a conductor if the specific pieces of music they are playing are suitable to this, and if the group is small enough and if they rehearse thoroughly enough to agree upon and memorize how they are going to interpret all the changes in rhythms, tempos and dynamics that are indicated in the sheet music. This is because there is always a certain amount of latitude for interpretation in all sheet music, even if the composer tries to write in a lot of details.
I'm a chorister--I sing in choirs. Choirs need a conductor because choral music, particularly the kind that is sung with no instrument accompanying it, often has particularly wide changes in rhythm, tempo, and dynamics all the way through each piece. All of these elements are continually changing moment by moment. There is no way that 50 singers could agree upon and properly execute these kinds of interpretive elements of the music in a cohesive and coherent fashion unless there is one person to lead them.
There are groups and styles of music where the conductor is also one of the musicians and is playing an instrument while conducting. You may not notice this person because he or she is not standing in front waving their arms or a baton. With some choirs, the person playing the piano or organ is also the conductor. With some small orchestras, for instance with Baroque music, the first violinist or the harpsichordist is also the conductor. The other musicians are always watching, intensely listening to, and responding to the interpretive changes being created by the conductor-instrumentalist, whether the audience is aware of this or not.
In summary, if the music is complex enough, and it is written for flexible interpretation and constant changes and modulations of rhythm, dynamics, and tempos, then it requires one individual to be in charge of interpreting those elements and getting the entire orchestra to follow that person in live performance. This person is the conductor.
As for the question about sheet music with regard to symphony orchestras, the short answer is that generally a symphony orchestra is called upon to play a great deal of pieces of music in a season, with relatively little rehearsal for each performance. One orchestra will typically perform a completely different set of pieces of music with every concert. This is in contrast to a pop music group on tour which will perform the same small list of songs over and over again night after night. Such a group can memorize what they are playing. It would not be practical to expect symphony orchestra musicians to memorize such a vast quantity of music written by so many different composers over so many centuries, in so many different styles. Symphony orchestra players can play practically anything with relatively little rehearsal precisely because of their ability to read sheet music extremely well. It is a requirement of the job.
There are still dedicated conductors because they were at one time necessary. The way programs are selected, access to scores, and technologies are a changing/improving. Budgets are being slashed. Today a temporary conductor (ie different musician from the group for each piece) or no conductor can suffice.
Lux is a small choral piece. But even if it was sung by the ~360 person Mormon Tabernacle Choir it matters not because it is the same situation. The conductor is not keeping anyone together. The conductor may, as I stated earlier, be a good initiator. After that he has little to no actual contribution. The hand motions are way to vague for time keeping.
It does look really neat to have someone waving their hands though. And sometimes if he'd shake his head or flip his coattails, really cool!
Each singer knows their own part and is internally counting their own time (tempo, note, and duration). They are singing with the other singers. They could sing this in absolute darkness just a beautifully as they can with candle light or incandescent.
Andre Rieu is a wonderful example. He has an excellent 50-60 ppl orchestra who play some quite lovely, intricate and difficult pieces containing tempo changes, key changes, pauses, voice/instrument mixes, etc... And quite often he stops conducting mid-song, turns his back to the orchestra, and starts playing the violin. How in the world can those musicians continue to play without that little baton drawing imprecise circles in the air? It is a mystery to us all.
A conductor is almost useless during performance. They are supposed to be the initiator, timekeeper and reminder for rarely used instruments that their time is near to play.
They do good as the piece initiator. But then any of the musicians not currently playing could perform this minor duty. In a pop band someone counts to start the song...1, 2, 3, 4 ...
As a timekeeper conductors are so vague on the beat center as to introduce confusion if the musicians tried to actually follow them. There is no precision to what they do, which makes them basically useless. Compare the conductor's movements to their counterpart the pop music drummer. The drummer is machine methodical on the beat. Even non-musicians can follow the drummer's beat without actually realizing they are counting time.
To compensate for the poor contribution the conductor provides the orchestra musicians are steadily reading the music, counting the time themselves, and listening to the other instruments. They know their parts quite well. Rarely do they ever look at the conductor.
In practice any musician not currently playing could organize the group and provide feedback until they get acquainted with the piece and group.
Better to replace the conductor with a simple blinking light the audience cannot see. Or provide ear pieces to hear the beat. It would cost less and work better.
