An interval is the term for the distance in pitch between two notes. You count how far apart they are, as with C to D or C to G. It is the foundation for understanding how a melody moves, how a chord sounds, and at what height to stack a harmony.
Why do we need intervals?
The same two notes at a different distance sound different: bright, tense, or stable. C to G is a fifth and C to E is a third, for example. Stacking thirds gives a chord its major or minor character, and fifths are widely used for their sense of stability.
Measuring in semitones and whole tones
The distance between adjacent notes on the keyboard is a semitone. Two semitones make a whole tone. Intervals are worked out from how far apart notes are in terms of these semitones and whole tones.
Their role in melody
Melodies that move step by step to neighboring notes tend to sound smooth, while melodies with big leaps tend to be striking. Looking at a melody you like in the piano roll and checking the distances the notes travel gives you hints for writing.
Their role in chords and harmony
A chord is a stack of several intervals. Harmony is also created by choosing intervals against the main melody. Before memorizing theory, it is better to play two notes together and hear the difference for yourself.
Practicing in a DAW
Duplicate a single MIDI note and move the copy a semitone at a time while both play. Hearing where the sound changes connects the keyboard to your ears.
