“OF COURSE I KNOW IT’S UNISON,” the singer says. “I just thought the bass was out of tune!” No way—the bass is not out of tune, but the singer needs a quick theory lesson. The word “interval” describes the pitch distance between any two notes; a large part of music theory involves learning the intervals. The unison actually is an interval: It consists of two notes of the same pitch, a fact that you should explain to your singer the next time you are recording with your band. As you auto-tune every note on his or her track, your singer will explain that “this is just how I hear things.” You might point out that music theorists call the unison a “perfect” interval—with good reason.

Example 1 is an overview of every interval known to bass-kind, all built from the note C. Why do you need to know about intervals at all? When you learn to understand and hear them, you’ll know why pretty chords are pretty, sad chords are sad, and funky chords make someone wiggle their whatzit. Intervals are the keys to recognizing, constructing, and playing all scales, chords, melodies and bass lines. You can construct any scale quickly by using whole-step and half-step intervals, and build any chord using your soon-tobe solid knowledge of 3rds, tritones, and perfect intervals—like that perfect unison your singer can’t quite nail.

Intervals are categorized as perfect, major, minor, augmented, or diminished. A perfect interval sounds stable and consonant, and when inverted (i.e., the bottom note becomes the top note or vice versa), it remains a perfect interval. There are perfect unison (PU), perfect 4th (P4), perfect 5th (P5), and perfect octave (P8) intervals. Major and minor intervals are the two main variations of all other intervals in a diatonic scale. Aside from the unison, the minor 2nd (m2) is the smallest possible interval; it comprises two notes that are a distance of one half-step apart—for example, the notes C and Db. The major 2nd (M2) interval comprises two notes that are a distance of two half-steps (or one whole-step) apart, such as the notes C and D. “Augmented” describes a perfect interval with an extra half-step added, and “diminished” describes one that has been reduced by a half-step.

One oddball interval is the tritone (TT), also known as the augmented 4th or diminished 5th (you may also hear it called the #4 or b5). Early composers and musicians called the sound of a tritone diabolus in musica, “the Devil in music.” The tritone interval consists of two notes placed three whole-steps apart, such as C and F#, or A and Eb. Like octaves and unisons, invert a tritone interval and you get the same thing: a tritone interval.

Go through all of the intervals in Ex. 1, noting that each successive interval is a half-step wider thank the previous. Finally, you reach the interval of 12 halfsteps, which makes up a perfect octave— the bassist’s best friend.

Intervals are always measured by the number of half-steps between the two notes. Let’s look at two of the most important intervals: the minor 3rd (m3) and the major 3rd (M3). Example 2 shows the distance of three half-steps in the m3 interval, the notes C to Eb. Check out the m3 interval all over the bass: Play any note, go up or down three half-steps (or three frets), and play the second note. It is very good practice to sing the intervals as you are playing them, precisely matching the pitches (something else you can suggest to your singer).

The M3 interval is constructed with four half-steps, or two whole-steps, between the notes (Ex. 3). Play any note on the bass, and then play the next note a M3 interval above or below.

Example 4 shows various m3 and M3 intervals. See if you can find m3 and M3 intervals all over the bass by fingering any note, and then playing the minor or major 3rd above or below that first note.

Example 5 is a 12-bar blues in G that uses loads of m3 and M3 intervals. (Go to bassplayer.com for the play-along track for this exercise.)

Intervals are the bricks and mortar that make up the sound of every chord and scale. When I create a bass line or solo, I am often not thinking of the chord names; rather, I am “hearing” the correct intervals internally, and matching those intervals on the bass. Learn intervals well and you will be able to play exactly what you are hearing in your head. In the next two Woodsheds, we will marvel at perfect intervals, and venture into the dark territories of the tritone, diabolus in musica.

John Goldsby’s newest release, The Innkeeper’s Gun, is out now. Also check out his other recent releases as bandleader, The Visit and Space for the Bass [all on Bass Lion]. John is the author of The Jazz Bass Book [Backbeat Books] and Jazz Bowing Techniques for the Improvising Bassist [Aebersold Jazz]. For more info, visit his website at www.johngoldsby.com.