|Lessons in Ear training|
What's a Chord? 
A chord is made up of several musical pitches played together to produce harmony. To understand chords, it's helpful to first understand intervals. There are two main categories of chords in Western music: triads and seventh chords. A triad is a chord made up of three pitches played together, each being an interval of a third apart. A seventh chord is made up of four pitches played together - a triad plus an additional note that forms the interval of a seventh above the root of the chord. There are other less common catagories of chords as well, including ninth chords, eleventh chords, and thirteenth chords, but they are less common.
Chord terminology and structure 
Every chord consists of several pitches (notes) played together. In a triad, the lowest note is called the root, the middle note is called the third of the chord, and the top note is called the fifth of the chord (the order changes if the chord is inverted - a common practice discussed later). A seventh chord is the same, except that it also has a seventh, making it a four-note chord. The third, fifth, and seventh of the chord are so called because they form the interval of a third, fifth, and seventh above the root, respectively. Therefore, in a C major triad (which is made up of C, E, and G played together), C is the root of the chord, E is the third, and G is the fifth. In a C dominant seventh chord (C, E, G, and B-flat), C is the root of the chord, E is the third, G is the fifth, and B-flat is the seventh.
Starting at the lowest note and working up, every consecutive note in a triad or seventh chord is an interval of a third apart. Keep in mind that a third can be a major third or a minor third. Whether each third is minor or major determines the chord type.
The common types of chords are listed below. In a chord name, such as "D minor triad", the chord type is "minor triad", and the chord pitch is D. Since each chord has more than one pitch, the pitch of the chord's root determines the letter name given to the chord. So a "B major chord" is a major chord whose root or lowest note is a B (again, we are assuming that the chord is not inverted).
Common types of chords 
Major triad 
One of the most common triads is the major triad or major chord. Using an instrument that can play more than one note at a time, like a piano or guitar, play the following notes at the same time: C, E, G. You've just played a major triad! If you don't know how to play these notes, ask someone else to play them for you. Listen to the chord carefully. Many people describe the chord as sounding "happy", as opposed to the minor chord (below), which sounds "sad". You can also hum the first few notes of the song On Top of Old Smokey. The notes that go with the words "top", "of" and "old" are the three notes that make up a major triad, although obviously you can't hum all three at the same time.
The above instructions tell you how to play a major triad starting on C, meaning that C is the bottom note or "root" of the chord. That chord would be called a "C major triad". So, a major triad with F as its root would be called an "F major triad". Like any other chord, a major triad can start on any pitch (A, F#, G-flat... you name it), as long as the interval between each note is the same. In a major triad, the distance between the root and the third (the bottom two notes of the chord) is a major third, which is four half-steps or four consecutive piano keys (counting both white and black keys) apart. The distance between the third and the fifth (the top two notes of the chord) is a minor third, which is three half-steps apart.
Minor triad 
Another very common triad is the minor triad or minor chord. You can play a minor chord by playing these notes simultaneously: C, E-flat, G (C-minor triad). If you prefer to use only the white keys on the piano, you can play these notes instead: D, F, A (D-minor triad). This chord is often described as sounding "sad", compared to the major triad.
The interval between the root and third of a minor triad is a minor third, and the interval between the third and the fifth of the chord is a major third.
A minor chord is usually written with a lower-case m after the chord name. The examples above would be written as Cm or Dm.
Diminished triad 
A diminished triad is constructed by stacking two minor thirds. An example on the keyboard would be the notes B D and F sounded simultaneously. Diminished triads are found on the seventh scale degree of any major key (i.e. the B triad in the key of C major). Diminished triads are found on the second scale degree in all minor keys, and on the seventh scale degree of harmonic and melodic minor keys but NOT natural minor (A.K.A. Aeolian mode).
Augmented triad 
An Augmented Triad is just a major chord that is made larger. The fifth of the chord goes up by one half-step. For example, a C augmented chord, written Caug, is C, E and G#.
Dominant seventh chord 
A Dominant Seventh chord, written with a 7 after the chord name, is a major chord with a minor 3rd added. For example, a C7 chord is C E G and B flat. The Dominant Seventh chord is one of the 3 important chords to know for any key, the others being the Tonic chord and the Subdominant chord. The Tonic chord will be built on the first note of the scale, and Subdominant chord built on the 4th degree of the scale, and the Dominant Seventh chord built on the 5th degree of the scale. So in the Key of C, the Dominant Seventh chord would be G7, with the Tonic chord being C and the Subdominant chord being F.
Major seventh chord 
Minor seventh chord 
Half-diminished seventh chord 
Fully diminished seventh chord 
Other types of chords 
Ninth chords 
A chord with more notes added than a 7th chord is called an upper extension chord.
A 9th chord is a 7th chord with the 9th added. For example, a minor 9 consists of 1 b3 5 b7 9. E minor 9 is E G B D F#
Eleventh chords 
Chord inversions 
A Chord can be inverted by changing the order of notes.
Triad of C major Chord(3 notes chord)
Root position : C,E,G
1st inversion : E,G,C
2nd inversion : G,C,E
Chord of G Seventh Chord (4 notes chord)
Root position : G,B,D,F
1st inversion : B,D,F,G
2nd inversion : D,F,G,B
3rd inversion : F,G,B,D
Methods of chord ear training 
Learning with an instrument 
Here are some basic steps for learning to identify common chords by ear.
- Step 1: Pick two or three types of chords to start with, like major triad and minor triad (I recommend starting with these two). Learn to play these chords yourself on an instrument that can play at least four notes at once. In the section above titled Common types of chordsare instructions on how to play each type of chord.
- Step 2: Listen to the chords you've just learned as you play them. Notice any differences in sound between them. For example, a major triad sounds "happy" to many people, whereas as minor triad sounds "sad".
- Step 3: Learn to distinguish between the chords you've learned. One way to do this is to have someone else play the chords one after the other at random, and see if you can identify which one is being played without looking at the instrument. Do this until you can consistently guess which chord is being played just by listening to it. Now you can go back to step one and repeat this process with two or three new chords.