COUNTERPOINT GENERATOR
COUNTERPOINT GENERATOR
THE IDEA
The program creates a 3 minute, 1O second long piece of music following the rules of 3rd species counterpoint in ABA’ format. There is a Cantus Firmus in whole notes (kind of like a bass line that determines the chord notes of each measure) and a melody above it in quarter notes.
Upon opening the program, users are met with the following message:
STEP 1: SELECTING A KEY
The first instance of randomness is the key picked. A random number in the range of C1 to C3 is picked, and then a 5 octave major scale is formed around it. Another major scale is developed based on the fourth note of that scale for later use in the B section.
STEP 2: CREATING THE CANTUS FIRMUS (CF)
In counterpoint, CFs generally have step-wise movement, can jump a third, and generally don’t go over a fourth. If there is a leap of a fourth, it should be followed by step-wise movement in the opposite direction.
Here are a couple examples of a standard CF in a major scale:
Following those interval probabilities and rules, I created a function that selects movement based on weighted randomness:
STEP 3: CREATING THE MELODY
The melody gets a bit more complicated. Every first beat of each measure should be consonant, meaning the interval between the CF and the melody should be a third, a sixth, an octave or unison, or a fifth——never a fourth or something else that’s dissonant. The following chooses an interval with preference to thirds and sixths:
Based on that randomly chosen interval, the rest of the measure is based on that first note. To make my job easier, I picked randomly from one of these common note patterns (8 total if you do the reverse directions, ex. scale going up):
An example of a neighbor pattern in the program:
The following is how I avoided the melody line surpassing an octave in range (another counterpoint rule):
Another important rule in counterpoint is that sections must end with a Perfect Authentic Cadence. Both the CF and Melody end with contrary motion to illustrate the following in any key:
For this, I tacked on a for loop (called .do in SuperCollider) of stepwise motion up in the second to last measure of each phrase
STEP 4: PUTTING IT ALL TOGETHER
I use three arrays per part to keep track of each section of the piece, then add each to one complete melody array and one CF array. Each array/track is in MIDI note format.
Put it all together and…
Here is a sample output (at tempo 20/60, slightly faster than the typical output tempo of 15/20):
and its corresponding arrays in MIDI (SC postln only lists up to 1OO values):
Cantus Firmus: [ 64, 66, 64, 63, 59, 61, 57, 56, 57, 56, 57, 68, 69, 68, 66, 64, 69, 66, 69, 73, 71, 68, 69, 68, 71, 74, 76, 73, 74, 73, 71, 69, 64, 68, 73, 71, 75, 73, 69, 73, 69, 73, 69, 68, 69, 68, 66, 64 ]
Melody: [ 71, 68, 69, 71, 69, 68, 71, 69, 73, 75, 76, 78, 66, 64, 68, 66, 63, 66, 64, 63, 64, 68, 66, 64, 61, 57, 59, 61, 64, 66, 64, 63, 61, 59, 63, 61, 59, 61, 57, 59, 61, 64, 63, 61, 71, 69, 71, 73, 78, 80, 78, 76, 71, 69, 73, 71, 69, 66, 68, 69, 71, 73, 75, 76, 76, 80, 78, 76, 74, 76, 78, 80, 73, 74, 73, 71, 76, 73, 74, 76, 74, 73, 74, 76, 71, 69, 73, 71, 76, 74, 76, 78, 80, 83, 81, 80, 80, 78, 80, 81, 83, 85, 83, 81, 80, 78, 80, 81, 81, 85, 83, 81, 83, 80, 81, 83, 76, 78, 74, 76, 80, 78, 80, 81, 76, 78, 80, 81...etc...
B section CF: [ 69, 66, 69, 73, 71, 68, 69, 68, 71, 74, 76, 73, 74, 73, 71, 69 ]
B section melody: [ 76, 80, 78, 76, 74, 76, 78, 80, 73, 74, 73, 71, 76, 73, 74, 76, 74, 73, 74, 76, 71, 69, 73, 71, 76, 74, 76, 78, 80, 83, 81, 80, 80, 78, 80, 81, 83, 85, 83, 81, 80, 78, 80, 81, 81, 85, 83, 81, 83, 80, 81, 83, 76, 78, 74, 76, 80, 78, 80, 81, 76, 78, 80, 81 ]
REFERENCE
/* Counterpoint is a traditional method of Western classical composition following various sets of strict rules. This program uses one set of those rules to create a 3 minute piece of music in ABA’ form using the coding language SuperCollider. */
This program was completed as an assignment for the course Computer Music: Algorithmic and Heuristic Composition (CPSC 431) taught by Professor Scott Petersen at Yale University.