Now that we are familiar with diatonic intervals, we need to look at the intervals that are non diatonic; the chromatic intervals. When describing chromatic intervals, we will endeavour to give context to every interval. As the major scale is our point of reference, we will nominate a key in which to compare the interval, in regards to its diatonic or chromatic status.
By definition, the term Diatonic refers to Belonging. That is, belonging to notes of the scale. Chromatic is the exact opposite to diatonic. Chromatic describes any note within a given scale that has been altered or coloured by accidentals (sharp, flat and natural signs). Chromatic notes are said to be outside the given key.
Since the major scale continues to be our point of reference, lets take a moment to review our rules for major scale construction:
- The notes of the major scale will follow the order of the musical alphabet
- You will not find two of the same letter names (scale degree) within the same scale; for example, Eb and E cannot exist within the same scale. The correct choice here would be D# and E
- Major scales do not mix accidentals
The rules above are not restricted to major scale construction. We can use these rules for determining whether an interval is chromatic. Lets look at some examples to see this in effect.
The simplest defining factor for chromatic intervals is that of scale degree. For example, the interval of C - C#. Remember, our rules state that you will not find two of the same letter names (scale degree) within the same scale. As both notes of this interval share the same letter name, we can conclude that it is indeed a chromatic interval. Specifically, this is an example of an augmented unison.
The above interval, C - C#, is an example of an augmented unison. From a half-step/whole-step perspective, this interval can be referred to as a chromatic semitone (one half-step). We have altered the quality of the note without changing the scale degree and hence, preserving its letter name, C.
The next defining factor is that of Key Signatures. Lets consider the interval, F - G#.
As always, we need to reference the major scale for the purpose of naming intervals. Since the lowest note in this example is F, we need to reference the F major scale.
The F Major Scale
The key signature of F major is one flat, B $ . The rules for major scale construction state, major scales do not mix accidentals. We can therefore conclude that F - G# is a chromatic interval. Specifically, this is an example of an augmented second.
Chromatic Intervals and Harmonic Relationship
The chromatic or diatonic status of an interval can be determined by comparing each note in relation to a given key. For example, when the key of C major is nominated, all notes within the interval are compared to C major.
Lets consider an example where the interval is identified as diatonic in one key and chromatic in another.
- C - Db is a minor 2nd and is considered diatonic in the key of Db major
- C - Db is a minor 2nd and is considered chromatic in the key of C major
When given a set of parameters, or in other words, a means to put things into context, we take away ambiguity and confusion, leaving us with the clarity to make an educated decision on interval quality and correct naming.
Different Point of View
We have focused on the major scale as our point of reference. This allows us to simplify and focus on the fundamentals of the subject. However, our reference scale is not limited to the major scale. When assigning diatonic or chromatic status to an interval, you may chose to reference any scale. For example the minor scale, pentatonic or even the exotic.
When altering a major or perfect interval, the following rules apply:
- Raising a major interval by a half-step creates an augmented interval
- Raising a perfect interval by a half-step creates an augmented interval
- Lowering a major interval by a half-step creates a minor interval
- Lowering a perfect interval by a half-step creates a diminished interval
- Lowering a major interval by a whole-step creates a diminished interval
Below is a list of the chromatic interval names, using the C major scale for reference
|Start Note||End Note||Interval Name||Equiv. Steps|
|C||C #||Aug. Unison||1|
|C||D $||Minor 2nd||1|
|C||D #||Aug. 2nd||3|
|C||E $||Minor 3rd||3|
|C||F #||Aug. 4th||6|
|C||G $||Dim. 5th||6|
|C||G #||Aug. 5th||8|
|C||A $||Minor 6th||8|
|C||A #||Aug. 6th||10|
|C||B $||Minor 7th||10|