Music Analytics:
Curtis Card Algorithms

Kelly Curtis

02/15/2017

In the 21st century, we find the world is a place of data. Data to transform, analyze, and digest. Data is everything these days. Data, data, data!

What if we decided to give the Musical Arts a chance to benefit from all these great techniques that are being researched in the data and computing world?

That is the attempt of these articles, to use modern analytic techniques against a data source that inspires so many people; American Jazz from the first half of the 20th century.

A system was developed to study lead sheets from that era of Music to determine if there were any patterns that could prove actionable for musicians seeking to learn and master this particular style. While Jazz is the focus of this article, these techniques, and the system built can be applied to other written sources of Music.

Let's review some basics about chord theory because Jazz is founded mostly on chord theory. This is not meant to be a introduction, and it is assumed the reader understands the basics of the symbols and their meaning in sound production.

C Major Scale

A major scale (Ionian mode) is a series of 7 notes progressing from a root (C in this case) up 7 notes in a pattern (R-2-2-1-2-2-1-R) of full (2) and half (1) steps.

C Major 7th Chords

If we take the major scale and we stack it by the natural 3rds in the scale and go up 4 notes this way (C-E-G-B), we start forming harmonies that derive from the root of the scale (C). Since the harmony is derived from this sequence, labeling the harmony in a general pattern (IM7, II-7, III-7, IVM7, V7, VI-7, VII-7(b5), IM7) that will apply to all major scales is found. This forms chord symbols that are used primarily in Jazz or any tonal based music(CM7, D-7, etc).

C Major 7 (CM7)

Using the major scale as the basis for all chord symbols is a convenient way to simplify the complexity of analyzing the symbol. In this case, we can then label chord as (R (1), 3, 5, 7) because these are the nature notes that would be found in a C major scale (C, E, G, B).

D Minor 7 (D-7)

Using the major scale as the basis for all chord symbols is a convenient way to simplify the complexity of analyzing the symbol. Repeated on purpose. In this case, we can then label the chords as (R (1), b3, 5, b7). We use the b3 in this case because if we use a major scale basis, the natural 3 is F sharp (F#), but in the case of D-7, it is F natural (F), which is one half step or semitone down from the natural 3, so b3.

Presented above is a list of a standard set of 7th chords that have C as the root (R) of the chord. Based on chord symbols found in Jazz literature. Different spelling may be available, but for the purposes of this discussion, this is the symbols set that was used:

R = Root

RM7, R-7, Ro7, R+7, R7, R7s4, R-7(b5), R-M7, R6, R-6, RM7(b5), RM7(#5)

Tensions:

Since using a major scale as the basis for all analysis of tones above a given root, there can be many alterations that may occur if we continue to stack in 3rds above the 7th of the chord symbol. These notes that are above the 7th when stacked in this fashion are called tensions.

Here is the list of tensions that are used in these analytic sheets:

CM7 Base

b9 (Db), 9 (D), #9 (D#),

11 (F), #11 (F#),

13 (A), b13 (Ab), b15 (Cb),

and 10 (E), 7 (B) in special cases).

The same tensions apply to every chord type, even if there is overlap with notes. This is to make analysis easier.

This is how we see chord symbols used in Music based on lead sheets. Looking at the image, the notes are labeled underneath according to their function in relationship to its root. In this case, all the notes are able to be assigned a function; there are cases where passing and neighbor tones may present a tone that does not fit the normal assigned function.

This image also contains the basic analysis of this music, which is IM7, II-7, V7, IM7. There are many known patterns in Jazz, and the two most common would be the 2-5 and the 2-5-1 patterns. These denote relationships between the Root and Chord functions over a 2 or 3 chord progression. A 2-5 or a 2-5-1 may exist without actually being the 2-5 or 2-5-1 in the Key of the piece (C is the key in the example. It can be a 2-5-1 for extended dominant funciton, say A-7 > D7 > G7. Even though G7 is the landing chord of the 2-5-1 pattern, it still fulfills the requirements for a 2-5-1 resolution pattern.

A 2-5 pattern is simply the relationship of a R-7 > R7 pattern. This can exist outside of the Key center of the piece as well. In the key of C, F#-7(b5) > B7 would still be considered a 2-5 pattern even though it is unnatural in the key of C.

The Curtis Card

Here is where it all comes together and starts to have some value. What if there was a tool that would automatically analyze music and spit out the function of the melody line and common patterns in the harmonic progressions?

This is what was built internally at Michael Kay Media, and is a new prototype designed to help study music patterns from written musical sources. This output shows you how the algorithms were able to find 2-5, 2-5-1 and a host of other patterns. It is called a Curtis Card.

In addition to figuring out chord progression patterns, it detects the melodic lines and assigns the function of that note against the chord symbol. Example, the melody notes in the red boxes above show us 5 C, 13 D, 7 E is that the melody line is C D E, but if you remove the note name, you get just 5, 13, 7 which is the melodic pattern in numeric form. This kind of analysis can be used in any musical style where the music can be reduced to chord symbols and melodic lines.

This is meant to be an introduction to part two of this article series talking about music analytics. In the next part, we take this information and study it across multiple pieces of Music.

Thank you for reading and if you are interested in discussing any of this, feel free to contact me.

Thank you!

Kelly M. Curtis

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