iviosab / music-accompaniment-generator Goto Github PK

• The fixed length of each chord in the individual is one quarter.

• Population: list of individuals.
• Individual: list of chords.
• Chord: list that consists of 3 notes.
• Note: an integer number that represents the midi value of a note.

• Be similar to the original melody in terms of flow.
• Not be in the same octave as the original melody to avoid dissonance.
• Have the chords follow the original melody's key.
• Avoid having the same chord played consecutively for too long.

• We keep the best 50% of the previous generation.
• We produce the other 50% of the population from the best 50% of the previous generation.

• We have a relatively high mutation probability which is 5% for each chord in the individual.
• We mutate by replacing a chord in the individual with an entirely new random chord.

• Used to parse the input midi file to readable values of notes and times.
• Used to write the output file using the tracks of the input and the generated accompaniment.

• Used to detect the key of the input melody to help us in the fitness function.

• Used to help us execute various random operations.

Representation:

• The population is represented as a list of possible individuals (accompaniments).
• Each individual is a list of N chords , the individual represents a possible solution to the problem.
• Each chord is a list of 3 notes, the chord represents a chord from the following set of chords:
  • Major triad, Minor triad.
  • First inverted major triad, First inverted minor triad.
  • Second inverted major triad, Second inverted minor triad.
  • Diminished chord.
  • Suspended second chord.
  • Suspended fourth chord.
  • Rest.
• Each note is an integer number that represents the midi value of a specific note.
• Each chord object is played for one quarter duration which equals 384 in the mido library time units.

Fitness function:

• The fitness value of an individual depends on three aspects:
  • The similarity of each chord in the individual to the average note played in the same quarter of the original melody in a lower octave.
    • While for empty quarters we calculate the similarity to the average note played in the next quarter that does play some notes.
    • To avoid dissonance we change the target average we want to reach to the same melody but shifted 2 octaves below the original melody.
      • For example if we have an average note played in a quarter of the original melody that is equal to C5. We make the targeted average be C3.
  • The existence of each chord of the individual in the possible chords we can compose out of the original melody key.
    • Based on that a valid chord of some key is three notes that start from a root note in the table and between a pair of consecutive notes we skip a note. e.g : I-iii-V in major, i-III-v in minor.
  • The similarity of each chord in the individual to the previous two chords in the individual. Where we:
    • Punish the individual for having more than two consecutive chords that are the same.
    • Reward the individual for having exactly two consecutive chords that are the same.

Selection technique:

• Selection method: Tournament.
• The selection phase selects half of the population to remain, the other half we remove from the population.
• Selection process:
  • We select half of the population based on a random tournament bracket, where random pairs of individuals are put ahead of each other.
    • The Winner gets added to the next population.
    • The Loser is removed fully.

Crossover technique:

• Crossover method: n-point crossover.
• The crossover phase chooses two random parents from the selected individuals. And they mate and produce two children.
• Mating process:
  • We iterate through the chords of the parents and do the following with a 50% probability:
    • Child1 gets the chord from Parent1, Child2 gets the chord from Parent2.
    • Child1 gets the chord from Parent2, Child2 gets the chord from Parent1.

Mutation technique:

• Mutation method: replacement of a chord with a random new one.
• The mutation phase takes the new children produced by the crossover phase, mutates them, and then returns the mutated children.
• Mutation process:
  • We iterate through the chords of the child and with a 5% probability:
    • we replace the current chord with a new random chord based on a random root and a random octave

Population Size:

• Population size = 1024
• The population size is set before running the evolutionary algorithm, and at the end of each generation we get a new population with the same size.
• The population size I found most suitable is 1024, because:
  • Less than that might lead to getting stuck in local maxima.
  • More than that would make the code very slow.
• The population size needs to be a number that is divisible by two because:
  • The selection phase selects half of the population size
  • The crossover and mutation phases generates a new half of the population
• If the population size is not an even number some errors might occur.

Stopping Criteria:

• Due to the fact that there is no clear definition of "perfect" music, I opted with the maximum number of generations method.
• The maximum number of generation method makes the evolution run for a set number of generations and then terminates.

Number of generations:

• Maximum number of generations = 5000
• The number of generations I found most suitable is 5000, because :
  • Less than that would not lead to a relatively good generation.
  • More than that would not lead to a significantly better generation.

Generation Time:

• The generation time depends on:
  • Population size.
  • Length of individuals.
  • Number of generations.
• On average the generation times for each input is:
  • Input 1:
    • Population size = 1024
    • Length of individual = 29 chords
    • Number of generations = 5000
    • Generation time = 20 minutes
  • Input 2:
    • Population size = 1024
    • Length of individual = 32 chords
    • Number of generations = 5000
    • Generation time = 23 minutes
  • Input 3:
    • Population size = 1024
    • Length of individual = 44 chords
    • Number of generations = 5000
    • Generation time = 36 minutes