Tone combinations are classified in music with names that identify the pitch relationships. Learning to recognize these combinations by both eye and ear is a skill fundamental to basic musicianship. Although many different tone combinations occur in music, the most basic pairing of pitches is the interval.
Interval
An interval is the relationship in pitch between two tones. Intervals are named by the number of diatonic notes (notes with different letter names) that can be contained within them. For example, the whole step G to A contains only two diatonic notes (G and A) and is called a second.
The term octave refers to the number 8, its interval number.
The interval numbered “1” (two notes of the same pitch) is called a unison.
Perfect, Major and Minor Intervals
The intervals that include the tonic (keynote) and the fourth and fifth scale degrees of a major scale are called perfect.
In addition, the unison and the octave are called perfect.
The intervals from the tonic (keynote) in an upward direction to the second, to the third, to the sixth, and to the seventh scale degrees of a major scale are called major.
When a major interval is made one half step smaller, it becomes minor. This can be done either by raising the bottom note or lowering the top note.
Notice the standard abbreviation for minor intervals: a lower case “m” followed by an interval number.
Consonance and Dissonance
We will define the term consonance in a musical sense as intervals that are treated as stable and not requiring resolution. The consonant intervals are the P1, m3, M3, P5, m6, M6, and P8. All other intervals within the octave are considered dissonant.
Augmented and Diminished Intervals
If a perfect or major interval is made one half step larger (without changing its interval number) it becomes augmented. If a perfect or minor interval is made one half step smaller (without changing its interval number) it becomes diminished.
Notice the standard abbreviations for augmented and diminished intervals. For example, d3 = diminished third and A3 = augmented third.
Enharmonic Intervals
Enharmonic intervals are intervals with the same sound that are spelled differently. Such intervals result, of course, from enharmonic tones. All of the following intervals sound identical but are spelled differently.
You must take care in spelling intervals. If a specific interval is requested, the enharmonic equivalent spelling is not correct. Thus, if a major third above E is called for, A- flat is not correct, even though it sounds the same as G-sharp. If a perfect fifth above F is called for, B-sharp is not correct, even though it sounds the same as C.
The Tritone
The most common enharmonic intervals are the augmented fourth and the diminished fifth, which divide the octave into two equal parts.
These intervals are usually referred to as the tritone, since they contain three whole steps.
Inversion of Intervals
The inversion of an interval means that the lower tone of an interval becomes the higher tone, or the higher tone becomes the lower tone.
Compound and Simple Intervals
Intervals greater than an octave are called compound intervals. These intervals are named in a similar manner to the intervals within an octave (simple intervals).
Applications
It is vital that you develop speed and accuracy in the identification and spelling of intervals. Much of your future work in music theory will require this ability. Many musicians use the following method to help them identify intervals more quickly.
1. Notice in writing thirds, fifths, and sevenths that the two notes are either on lines or on spaces.
2. Seconds, fourths, sixths, and octaves involve a note on a line and a note on a space.
3. Fourths, fifths, and octaves are perfect if the accidentals are the same, except for the fourth and fifth involving B and F.
4. Seconds are major, and sevenths are minor if the accidentals are the same, except for those involving E–F and B–C.
5. Thirds built on C, F, and G are major if the accidentals are the same. Thirds built on the remaining notes are minor if the accidentals are the same.
6. Sixths whose upper tones are C, F, or G are minor if the accidentals are the same. Sixths whose upper tones are any of the remaining notes are major if the accidentals are the same.
7. You can quickly determine other interval qualities by reducing the interval to the “same accidental” form and then noting the effect on interval size when the accidental(s) are replaced.
With sufficient practice, determining the size of intervals will become automatic.
Melodic and Harmonic Intervals
The two pitches of an interval will occur either in succession or simultaneously. If two tones are positioned adjacently and sound one after the other, the resulting interval is considered to be melodic.
If two tones sound at the same time, the resulting interval is said to be harmonic. Figure below demonstrates a series of harmonic intervals occurring between the left-hand and right-hand parts of a keyboard composition.
Although most harmonic intervals are aligned vertically, unisons and seconds require offset positioning. Notice that the noteheads of harmonic unisons and seconds touch, but never overlap.
Transposition
Transposition is the process of rewriting a piece of music or a scale so that it sounds higher or lower in pitch. This involves raising or lowering each pitch by the same interval.
Method 1: Interval Transposition
One common technique for transposition is by interval. In this method an interval of transposition is established, and all pitches are moved up or down by that interval.
and there are many more methods to transposition but in MEE Grade Examination only Method 1 is in Syllabus.