Intervals  (Part Two) Lesson by flyinglibra51

Unisons, Octaves, fourths and fifths

These all use the terms Perfect, Augmented, or Diminished to identify
their Quality.

Perfect Unisons
A perfect melodic unison is the easiest move you can make on a guitar. Go to the 5th fret on the low E string (6th) hit one note and then hit the 5th string (A) open. You have just played two A notes in Perfect Melodic
Unison.

Augmented Unisons
To make a perfect unison Augmented, you add one half step between the two notes. You can alter either note the half step by using a sharp or
flattening. Bb to B is called an Augmented Unison (or augmented prime)
unison because the interval is one half step greater than a perfect unison

A Diminished Unison doesn't exist because no matter how you change them
with accidentals, you're still adding half steps to the total interval.

Octaves
When you have two notes with an interval quantity of eight lines and
spaces, you have an Octave.
A Perfect Octave is a lot like a perfect Unison in that the same note
has 12 half steps between it.

To make a perfect octave Augmented, increase the distance between the
notes by one more half step, or decrease the low note by one half step.

To make the same Octave Diminished, decrease the distance between the
notes by one half step. (11 and 1/2 steps) You could also raise the
bottom note by one half step.

Fourths are pairs of notes separated by four lines and spaces. All
fourths are perfect in quality, having 5 half steps between notes,
except for the fourth from F natural to B natural, which has 6 half 
steps. ( making it an augmented 4th)

You can create a perfect 4th between F and B by raising the F to F#
or lowering the B to Bb. The natural 4th is perfect, adding a # or a b
to both notes doesn't change the intervals quality.

Fifths
5ths are Perfect containg 7 half steps. However, B to F is a diminished
5th which sounds like an augmented 4th (only 6 half steps)
You can make the perfect by adding a half step to either note, Bb or F#
This  time the size of the interval is increased.

flyinglibra51
God Bless Glen Travis Campbell