Building Chords in a Step Sequencer

When you make music with a step sequencer, it's real easy to build chords without having to look at any chord chart or use any chord making tool. Here, I am gonna talk about major, minor, diminished, and augmented triads but this extends to all types of chords.

The step sequencer's piano roll is divided into cells. Each cell represents a half-step on the vertical axis.

A major triad chord is built with 3 notes: the root, a note that's 4 half-steps higher (major third) and a note that's 7 half-steps higher (perfect fifth). In integer notation, it's represented by the triplet 0-4-7. To build a major chord, you pick the root, place the 2nd note 4 half-steps up, and the 3rd note 7 half-steps up. From that major triad, you can build the minor, diminished, or augmented triads quite easily by shifting the 2nd and/or 3rd note by a half-step.

A minor triad chord is represented by the triplet 0-3-7. Starting from a major triad chord, all you need to do to get to the minor chord is to bring down the 2nd note by half a step.

A diminished triad chord is represented by the triplet 0-3-6. Starting from a major triad chord, all you need to do to get to the diminished chord is to bring down the 2nd note and 3rd note by half a step.

An augmented triad chord is represented by the triplet 0-4-8. Starting from a major triad chord, all you need to do to get to the augmented chord is to bring up the 3rd note by half a step.

Diatonic chords are chords made up of notes that are always within a given scale. The diatonic triad chords of a major or minor scale are always major, minor, or diminished. To build a diatonic chord for a given major or minor scale and a given root, you start with a major chord and either keep it as is or bring it down to a minor chord or diminished chord until all the chord notes are within the scale. So, basically, all you need to know are the notes of the scale you are working on (more on this below).

For a major scale, the intervals between the notes are as follows:
1-2-3-4-5-6-7-8 <- note degrees (positions within the scale)
-2-2-1-2-2-2-1- <- intervals (in half-steps)
Intervals 3-4 and 7-8 are just 1 half-step while all the others are 2 half-steps.

For a minor scale, the intervals between the notes are as follows:
1-2-3-4-5-6-7-8 <- note degrees (positions within the scale)
-2-1-2-2-1-2-2- <- intervals (in half-steps)
Intervals 2-3 and 5-6 are just 1 half-step while all the others are 2 half-steps.

There are 7 notes in a major or minor scale. The note at degree 1 is the scale tonic (it defines the scale). The note at degree 8 is the note at degree 1 raised by 1 full octave.