An interval is a difference between two pitches or notes.
We build all musical scales and chords with intervals. An interval can be melodic or harmonic. If it refers to successively sounding notes, we call it a melodic interval. Here is an example.
There are two half notes in this example. The first one is D and the second one is F. First of all, D sounds and then F sounds. It is a melody and this is why we call it a melodic interval. With intervals, the notes don’t have to sound successive. If an interval refers is between simultaneously sounding notes, we call it a harmonic interval. Here is an example.
There are two whole notes in this example. The lower one is C and the higher one is G. But this time they sound at the same time. Between these simultaneous sounding notes, there is a harmonic interval.
There are two basic steps of naming intervals. The first step is measuring the distance between two notes and the second step is naming it according to its quality.
Quantity Of Intervals
The first step of naming intervals is measuring the distance between two notes. Let’s have a look at the notes of our first example above on a piano keyboard and measure that interval.
In this example, D is the first note of the interval and F is the second note. If you look at this figure carefully, between D and F there are three half steps. These are D-D sharp, D sharp-E and E-F. While naming it, these half steps will be important. But to measure intervals, we only consider the number of note letters involved. As you can see, there are three different basic notes between D and F. They are D, E and F. So this is a third interval. Let’s see another example.
In this example, C is the first note and B is the second note. Between C and B there are eleven half steps and seven notes alphabetically. They are C, D, E, F, G, A, and B. This is why C-B is a seventh interval. Let’s see another example.
When two tones sounding the same pitch, usually at the same time, we call the interval between those notes unison or a perfect unison or a prime. In this example, you can see the unison interval which consists of two C’s. When we place the unison notes beside each other without any space like this, they are harmonic. Because of the fact that they have the same pitches, we can’t place one above other. This is why we place them beside each other. If, however, there was some space between them, like they are part of a melody, then the interval would be melodic. Let’s see another example.
In this example, you can see an octave or perfect octave. Notice that the name of the notes is same again. They are both C’s. But this time, the second note is an octave or 12 half steps higher than the first one. When we compare their frequencies, the frequency of the note with the higher pitch is twice of the frequency of the lower one.
Simple and Compound Intervals
Simple (or basic) intervals are unison, second, third, fourth, fifth, sixth, seventh, and octave. Intervals beyond an octave are called compound intervals.
Quality Of Intervals
In the next articles, I will explain all these intervals in details.