Modulation can be defined as the changing of key within a song (or chord progression). It is important to be able to recognise a modulation. In sheet music, a modulation is sometimes indicated by changing the key signature. This will usually be done if the modulation occurs between one section of the song and the next (e.g. between one verse and another). Where there is no change of key signature, a modulation may be detected by examining the melody and/or the chords. When examining the melody, remember that each key is recognisable by the notes of its scale. If different notes appear it may indicate a modulation. For example, if a melody in the key of C suddenly features F# notes, it could suggest a modulation to the key of G.
When examining the chords, a modulation may be identified by following the chord/key relationship, i.e. looking for chords that Tit into' a certain key. Consider the following progression.
It can be analyzed:
The use of Roman numerals makes the lay-out of this progression very clear. It is based on the IIm7-V7 chords, modulating through four different keys. This type of modulation is most common in Jazz. You will find that many Rock songs, although featuring modulation, will not do so to such a great extent.
One of the most common modulations in songs is from the major key to its relative minor.
Another is to change up to the key one semitone or one tone higher. This can be done successively, as in the this example: