i learned that all chords derived from the scale, how do i tell which the key signature of a chord is by look

Question

looking at it, also how do i tell what is the key signature of a piano music sheet is by looking at it, i know the far left shows u the number of flat and sharp but for example b harmonic minor scale and b melodic minor scale holds the same number of sharp (2) on the same two letter c and f, how can i tell then if the music piece is harmonic b or melodic b. also if there is no sharp or flat, how can i tell if it's an A natural minor scale or a m major scale cuz both of those have no sharp or flat, and also how do i look at a chord and know which scale or key signature the chord is in

Answer 1

To further define what key a piece of music is in you have to look at the melody and work it out from that. There is no simple way to determine if the piece is in A minor or C major just by looking at the key signature. The melody and chords (if they are given) will determine this.

You cannot tell the key of a piece just by looking at one chord. You could possibly determine the key if you had a number of chords but even then it may be ambiguous. It depends on the piece.

Answer 2

Pieces are not written in harmonic or melodic minor keys.
Rather, the harmony is in harmonic minor and the melody is in melodic minor.

For instance, the dominant chord of d minor is A major, which has a C-sharp. That is why there is a C-sharp in the d harmonic minor scale.

However, the melody is different. In the melody, the sixth and seventh steps are usually high going up and low going down.
In the key of d minor, this would be B-natural and C-sharp going up and C-natural and B-flat going down.

Try "Chim Chim Cheree."
http://kids.niehs.nih.gov/lyrics/chim.htm

On the words "blow me a kiss," the notes are 8 7 6 8.
In d minor, this is D C-natural B-flat A.

On the words "and that's lucky too," the notes are 5 7 8 high 2 8.
In d minor, this is A C-sharp D high E D.

This isn't a perfect example, because there aren't any ascending sixth steps in the song.
So I will have to ask to to accept on faith that the ascending sixth step is usually high.

Oh, yes, I almost forgot to tell you how to tell if a piece is in a major or minor key.
A quick and dirty way is to look at the last chord in the piece.
Nine times out of ten, the piece ends with the tonic chord--or the chord of the key that the piece is written in.
If you haven't learned yet how to recognize major and minor chords, just look at the last note in the melody.
Nine times out of ten, the last chord has do on the melody line.
In the example I just gave, the last note of the song is D, so you can tell it's in d minor instead of F major.

Answer 3

There is no way to determine key from a single chord. Nor is it possible to tell the difference between one kind of minor and another just from the key signature.

The scale comes in varieties, chromatic, major, natural minor, melodic minor and harmonic minor. Additionally, in early music and in jazz, scales based on the same intervals, but starting from different notes (such as a scale from D to d with no sharps or flats,) which are termed "modes", also have to be reckoned with.

The chromatic scale uses all the semitone pitches, and the only thing that establishes a "key" is the imagination of the composer. The primary clue is the note it starts and ends on, if it goes a full octave. Beyond that, it is just itself, chromatic, and pieces written to use all 12 of the notes within the octave (serial or tone row) generally don't bother with key signatures or pretense of tonality. Tonal pieces with chromatic scales in them generally have a key determined by other features of the music.

In music theory, it is customary to examine the diatonic scale and number the pitches: the lowest is generally numbered 1, so the octave is numbered 8. If chords are built up within the system established by this scale, then the intervals that make the chord will be determined by the intervals of the scale. For the major scale, this means that the triad (three-note) chord built on 1 will be a major chord: CEG, if 1 is C. This chord is notated in theory as I (capital i as a roman numeral), a major chord built on the first tone of the scale. Staying in the key of C, the chord built on the second tone (DFA) will be a minor chord, so it is written with a lower-case roman numeral; ii. Then, the chords on the major scale tones are:
I ii iii IV V vi vii-
The - indicates a diminished chord. Looking at these chords in turn, to see their intervals:
I CEG (a major third on the bottom with a minor third on top)
ii DFA (a minor third with minor third on top)
iii EGB (same intervals as ii, also termed Minor-Major because of the stacking of intervals)
IV FAC (major chord: same as I, also called Major-Minor)
V GBD (major)
vi ACE (minor)
vii- BDF (minor-minor, or diminished)

For the minor scale, the intervals are identical, but you start on a different note: for C major, the relative minor is A minor. This makes the scale from A to a, and the chords will be
i minor
ii- diminished
III major
iv minor
v minor
VI major
VII major

So if you have enough chords (generally 3) you can determine the key from that, to some extent. But there are crowbars in the works: the melodic minor has a major V chord, for instance, and the harmonic minor has rising major intervals, but falling minor intervals. So you always end up having to look at the melody!

Hint 1: Look at the key signature. This cuts the possible keys down to 2: major and minor. When I say minor at this point, I mean all of the possible minors.
Hint 2: Look at the last note of the bass (or bottom of the last chord, or name of the last chord if you only have chord charts or names.) This is most likely to be the key tone (much more likely than the melody's last note, which may end on the fifth tone of the scale or even third, or in more modern music, second or even fourth!) If the bass ends on a pitch that is not the major or minor that goes with the key signature, you have a mode!
Hint 3: Look at the melody for scale runs. Note if there are accidentals: these indicate that the key may be in question. Also, look for where cadences end. This is often a clue when modes are in use.