Key signatures define the prevailing key of the music that follows, thus avoiding the use of accidentals for many notes. If no key signature appears, the key is assumed C major /A minor, but can also signify a neutral key, employing individual
accidentals as required for each note. The key signature examples shown here are described, as they would appear on a treble staff.
Lowers by a semitone the pitch of notes on the corresponding line or space, and all octaves thereof, thus defining the prevailing major or minor key.
Different keys are defined by the number of flats in the key signature, starting with the leftmost, i.e., B♭, and proceeding to the right; for example, if only the first two flats are used, the key is B♭ major/G minor, and all B’s and E’s are “flatted”, i.e. lowered to B♭and E♭.
– Sharp key signature
Raises by a semitone the pitch of notes on the corresponding line or space, and all octaves thereof, thus defining the prevailing major or minor key. The number of sharps in the key signature, also proceeding from left to right, defines different keys; for example, if only the first four sharps are used, the key is E major/C♯ minor, and the corresponding pitches are raised.
Key signature is composed of sharps or flats located at the beginning of the staff. The sharps or flats are never combined in the same song. It is very important to know how to find the key of a song, especially in sol-fa work. The keynote and “doh” are the same.
If there are no flats or sharps written between the clef sign and the time signature then that song is written in the key of C Major. Any clef that has an accidental (sharps/flats) sign as its key signature check on the line or space of which those signs are been placed and you should know that any notes that falls on that line or space will sound in respect to the sign placed at the beginning of the stave as its key signature. E.g.
Now all the notes that fall on the fifth line of the staff above must be in sharp (e.g. F#) because a sharp sign have been placed on that line as its key signature as earlier stated. This staff is in the key of G.
Any note that falls on the middle or 3rd line and the 4th space will be in flat (E.g. B♭-E♭) because a flat sign has been placed on it as its key signature at its onset. This staff is in the key of B♭.
This does not end here but we will stop here so far. So it is on the staff notation and as we go on, you will notice it yourself without little or no help.