Intervals are the missing link in modern music education today as it is often presented as a purely theoretical concept that has no application to what you are actually playing. In fact, the importance of intervals is abundant and having this knowledge expedites the learning process on the bass guitar exponentially. Understanding intervals goes way beyond just comprehending diatonic intervals, but extends to the chromatic intervals as well. This knowledge, along with understanding the major and minor key centers is crucial for fast tracking your capacity for grasping applied music theory.
The term interval is used to describe the distance between two notes. Intervals are defined by the type of interval (2nds, 3rds, 4ths, 5ths, 6ths & 7ths) and the quality, which are major, minor, perfect augmented and diminished.
We start by using the major scale to determine the type of interval. The alphabet in Western music is A-B-C-D-E-F-G. These notes organized as a major scale would give us the key of C major: C-D-E-F-G-A-B. It is the distance between the letters of the major scale that determines the interval type. For example, C up to G is a 5th because G is the fifth note of the scale, where C down to G is a 4th because G is four letters down from C.
The type of interval does not change as the quality of the interval changes. For example, it doesn’t matter if sharps or flats are used, E up to B will always be some kind of a fifth and A down to G will always be some kind of a second.
The quality of the interval is determined by the number of semitones present in the interval. For example, a major 3rd is three letter names apart and contains four semitones, whereas a minor 3rd is also three letter names apart but only contains three semitones. A perfect 5th has seven semitones, while a diminished 5th has only six.
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Everything that you play is a combination of intervals in action that are cross applied to the harmonic progression that you are playing over. In the same way that inches, feet and yards measure the exact distance from one point to the next, both the type and the quality of intervals are used to measure the exact distance between two notes that you are playing.
All the Bass!
I don’t know why people insist upon starting with the major scale to teach intervals.
I started that way and got so thrown by out of key chords and not knowing how to match the major scale to them, but starting with the chromatic scale and by doing being able to explain, and more importantly have people playing chord changes right away without more than the most basic idea of how they are formed, seems the much better route.
So much music has borrowed harmony that it just makes more sense to me to almost ignore key at first other than what your ear is telling you anyway.