In piano arrangements of songs I am learning, the melody usually appear on top of the arrangement as I assume it sounds better having it there. I assume this is especially true of dissonant notes as I can often see that arrangers will try and make the dissonant note always at the top of the arrangement. Could someone explain if this is the case and what to do when you have a low singing voice? I am a bass-baritone so does that mean that if I want a good arrangement for my voice that the supporting harmony will have to be in the two lowest octaves so that my voice can sit on top? I wish I had more arrangements that actually had the correct octave placing for the melody but usually the low voices get transposed to the treble clef any way so this confuses me because I end up learning a transposed version of the song arrangement... maybe this doesn't matter but i fail to see how it doesn't.
Yes, the melody is more likely to have 'outside' notes than the accompanying harmony.
But look at some of the music you ARE singing. When a bass voice sings 'Old Man River' is he accompanied solely by cellos, double basses and bassoons? No, somehow the solo voice manages to 'lead' even though much of his accompaniment is in the treble clef! And, trust me, when accompanying a male singer on piano, I find no need at all to play with my left hand only.
An octave shift of the solo voice makes surprisingly little difference to whether it sounds 'on top'. Don't worry about it.
Whether or not the melody appears on the top of the arrangment depends on the arranger, and sometimes the style of the song. For example, in this song, "Speak to Me", by Tommy Walker:
The melody is represented as one line with the chords printed on top. In other songs the top note is at times not the melody at all but rather an an added note to add to the melody.
You'll notice some of the chords are 7ths, which means they have a clashing note at the top (for example Cma7 is C,E,G,B (on the top) , Em7 is E,G natural,B and D on the top) the clashing note is used to create tension, which is pretty typical in this style of music (it's light jazz or bluesey). Tension occurs when a chord sound "unresolved", for instance, this song keeps the tension going from the second bar to the 5th bar. G, the first chord is nice and resolved, Cma7 is where the tension starts, Em7 keeps tension going, the D chord doesn't resolve because the singer goes from a "B" (which clashes against the "A" in the D chord, to an "A" then to a "G" which clashes with both the "A" and the "F sharp" in the D. The C briefly resolves, but notice the piano part, the F sharp over D clashes with the C chord, the E over C gets you ready for the "G" chord which resolves the phrase.
As fas as the melody being transposed, sometimes , yes it is transposed, but let's make sure we have the same definition, because it seems like you may be defining it differently. In the song I showed you above, the melody line is shown in the treble clef (the right hand of the piano). This is typical of music writing, but it's not a transposition. This melody line is an octave higher (8 notes) than where the actual artist singing this song, he still starts on "G" (which is the printed starting note) but he starts 8 notes lower. It's still the same note however.
A transposition occurs when the music is not written using the same notes that the singer is singing in the recorded version. For example this is a transposition - that is, the song is not in the same key, the melody line doesn't start on the same note the singer does in the recording:
The melody line is totally different than the recorded version, the recorded version is actually this:
The singer's notes are totally different. That's a transposition.
As far as where your harmony should be, belive it or not, this depends on the song. Just for reference, I'm a keyboard player and a backup vocalist. Most of the time the harmony I end up singing is higher than the melody line, rarely is it ever lower. As far as where it should be in the music, that's really up to you as the arranger.
There's no real "rule" for what note it should be, except that it sounds good to you as the arranger. Typically, it should be the same key and should sound good, that's pretty much about it.
As far as the melody line being written in the treble clef goes, like I said, that's standard for music. The only time I've seen it written differently is in Choral music, where the bass clef is used for tenors and baritones / basses.
Hope I was able to help you out a bit.
Generally, a harmony serves as the foundation for the melody. The melody is almost always the highest note because high notes are more piercing, i.e. they stand out. The melody is the foreground, while the harmony is the background.
Think of any other aesthetic thing-- say a painting. You wouldn't paint a dark gray splotch in the middle of a vibrant background full of color. You'd pain your bowl of bright and highly-detailed fruits in the foreground, and keep the background simple so as not to distract from the theme.
Notes aren't dissonant in and of themselves. Dissonance is a relationship between notes. For that reason, I don't think it's even a well-defined idea to say that the more dissonant note is voiced higher.
In musical styles, like baroque, that treat dissonances as requiring resolution, you could look at whether a dissonance is resolved by having one voice move while other voices stay put. This may happen somewhat more often with the upper voice handling the resolution, but I don't think it's any kind of a general rule.
What would be considered a dissonance in older styles might in jazz just be treated as a color rather than something that needs to be resolved. One thing you'll see a lot in jazz is that with a pair of notes like F# and G, people will usually avoid voicing them so that they form a m2 or m9. So for example, in a C#11 chord, if you're going to include both the F# and the G, you would typically put the F# above the G, not below it. A chord like G maj7 is treated in jazz as a stable consonance when G is in the bass, whereas you would probably only see F# in the bass if the bass started on G and then started moving down a scale, stepwise.
There is a general feeling that chords sound best when their structure sort of imitates the overtone series. This feeling happens more when the spacing between the lower notes is wider, and when the lower notes are the root and fifth. Chords tend to sound muddy when the spacing is close in the lower notes. So for example, say a jazz arranger is going to voice a C major chord as C E G D (which in jazz is just considered a voicing, not some kind of special Cadd9 chord). They would probably not voice it with D in the bass and E immediately above that, simply because it would sound muddy.
In jazz, the bass line is usually improvised by the bass player, and the bass player will often try to land on the root of the chord on 1, so that everyone hears where the harmony is and where it's going. The piano player will often play the 3 and 7 of the chord in a middle register, because that defines the character of the chord and its harmonic function. They do these things kind of automatically in most cases, and the arranger doesn't write them out. So if the harmony is a triad or a 7th chord, the basic notes of the chord will mostly be heard in the low and middle register, just as a matter of performance practice.
A lot of these answers did a good job of addressing the part of the question about the melody being on top. I'm going to try some reasoning on where to put dissonant notes in an arrangement.
I don't think that putting dissonance on top is always the correct decision, actually. That's not even something I personally have heard of as an arranging guideline, although maybe some of you have? If anything, I think it's the middle parts that tend to get the more difficult dissonances the most often. In a barbershop quartet, it's usually the baritone who has the least intuitive part to sing. In choirs, it's the altos and tenors that do the most complaining about having parts that are hard to sing. I'd think that would make a case for the middle parts having the dissonances the most frequently. Middle parts tend not to have the melody: ergo, they have more dissonances than other parts.
There's some logic behind that, too. Usually, as mentioned and reasoned out more fully in other answers, the melody takes the highest spot most of the time in an arrangement. It doesn't have to be the highest voice, but it is usually not a bad idea to do this if it's possible, and all else being equal that helps the melody to be perceived as the lead to an extent. Thus, the dissonances have to be somewhere else. They also won't be in the bass as often, for the same reason that the bass is often seen as a kind of supporting countermelodic figure. It doesn't have as many dissonances, though it could certainly do so if needed. Thus, it's the middle parts that would naturally be filling in the complicated dissonances a larger percentage of the time.
Most of the above was in the context of singing arrangements, though. Does my stance ring true (pun intended) for instrumentals? The thing is, (large) instrumental arrangements tend to have wider ranges than arrangements for voice only - singers have some differences between them, but different instruments have entirely different acoustic anatomies. So with instruments, it may be less often that the absolute highest voice is doing the melody. Piccolos don't always play the melody! There are usually other factors more important than frequency that inform the arranging decision of where to state the melody. Actually, that's true of voices as well to a lesser degree.
One disadvantage of having the dissonances in the middle is that many arrangements pay special attention to modeling the harmonic series in their chord voicings. Ideally, the chord voicing is spread farther apart in the bass than in the treble, and the intervals generally get less and less consonant (in a Justly Intonated sort of logic) as they go up the overtone series. That would possibly discourage putting dissonant intervals in the middle, although again, this is not the only factor that goes into a decision about voicing. With dissonances on top, the chord is therefore probably able to have its notes' overtones reinforce each other more strongly.
To wrap this up, I'm of the opinion that in all arrangements there is no strong rule that dictates where either the dissonances or the melody should ideally be, and if there is a general trend in this regard, it is a weak one. There are lots of solid justifications for any particular arranging decision, and with regards to dissonance in voicings I've only walked upon two of them for this answer.
Besides, dissonance can have many meanings. Are we talking intervallic dissonances? Harmonic dissonances? Is a major triad a dissonance in the context of power chords? At the end of the day, I don't believe in a one-size-fits-all approach to voicing dissonance within an arrangement. In the study of arranging, I think it's more important to be able to understand what the intent behind a certain decision was rather than being able to forecast what that decision will be.