/// <summary>
/// Evaluates the ratio of extreme pitch intervals.
/// <para> This evaluation checks the pitch interval between every two consecutive
/// notes and check if the interval is considered extreme or not, in regard to the
/// <paramref name="maxInterval"/> parameter: If the interval is higher than the
/// max interval parameter, the distance between the notes would be considered as
/// an extreme distance. </para>
/// <para> Besides counting the amount of existing extreme intervals,
/// this evaluation takes into account the extreme level, i.e., how large in
/// terms of semitones the interval is, so a two octave interval is considered twice
/// as extreme than a one octave interval. </para>
/// <para> The overall fitness is a weighted sum of the ratio between the non-extreme
/// intervals to the total number of consecutive notes intervals, and the invert ratio
/// of total semitone distance in the entire melody and the max pitch range. </para>
/// </summary>
/// <param name="maxInterval"> Max interval that is considered "okay" between two
/// consecutive notes. Any interval that exceeds this one would be considered extreme.
/// </param>
/// <param name="candidate"> The melody candidate to evaluate. </param>
/// <returns> The fitness outcome score for the requested evaluation. </returns>
private protected double EvaluateExtremeIntervals(MelodyCandidate candidate, PitchInterval maxInterval = PitchInterval.PerfectFifth)
{
// initialize counters & accumuators
ulong totalNumOfIntervals = 0;
ulong numOfExtremeIntervals = 0;
ulong overallDeviation = 0;
int adjacentDistance = 0;
// init max pitch range
int pitchRange = MaxPitch - MinPitch;
// initialize metrics
double extremeIntervalMetric;
double overallDeviationMetric;
// convert max interval nullable int to int
int maxDistance = (int)maxInterval;
// retrieve and filter all pitches which are not hold/rest notes
NotePitch[] pitches = candidate.Bars.GetAllPitches().ToArray();
// accumulate extreme adjacent notes pitch distance
for (int i = 0; i < pitches.Length - 1; i++)
{
// calculate pitch distance between the two adjacent notes
adjacentDistance = Math.Abs(pitches[i + 1] - pitches[i]);
// if this pitch is extreme, update counter & deviation accumulator
if (adjacentDistance > maxDistance)
{
numOfExtremeIntervals++;
overallDeviation += (ulong)(adjacentDistance - maxDistance);
}
}
// set total number of intervals
totalNumOfIntervals = (ulong)pitches.Length - 1;
// calculate ratio of extreme intervals which exceed the requested max interval
extremeIntervalMetric = (totalNumOfIntervals - numOfExtremeIntervals) / (float)totalNumOfIntervals;
// calculate metric of overal deviation from max interval
overallDeviationMetric = (numOfExtremeIntervals == 0) ? 1
: numOfExtremeIntervals / overallDeviation;
// return weighted fitness according to the two different metrics
return((0.4 * extremeIntervalMetric) + (0.6 * overallDeviationMetric));
}
/// <summary>
/// Evaluates how "smooth" the movement is from tone to another.
/// <para> This evaluation is based on the intervals between consecutive notes
/// and the notes' degrees in context of their underlying chord.
/// According to the interval type (perfect, consonants, dissonant) and the
/// note's degree (chord note, diatonic note, etc) a weighted fitness is set. </para>
/// </summary>
/// <param name="candidate"> The melody candidate to evaluate. </param>
/// <returns> The fitness outcome score for the requested evaluation. </returns>
private protected double EvaluateSmoothMovement(MelodyCandidate candidate, PitchInterval maxInterval = PitchInterval.PerfectFifth)
{
// initialize counters
ulong totalNumOfIntervals = 0;
ulong numOfDiatonicSteps = 0;
ulong numOfChordSteps = 0;
ulong numOfDissonants = 0;
ulong numOfPerfectConsonants = 0;
ulong numOfImperfectConsonants = 0;
ulong numOfTritones = 0;
ulong numOfBigLeaps = 0;
int adjacentDistance = 0;
// initialize metrics
double diatonicStepsMetric;
double chordStepsMetric;
double intervalTypeMetric;
// additional initializtions
double fitness = 0;
double factor = 0.5; // factor for balancing this fitness function
PitchInterval interval;
int maxDistance = (int)maxInterval;
// retrieve and filter all pitches which are not hold/rest notes
NotePitch[] pitches = candidate.Bars.GetAllPitches().ToArray();
// accumulate extreme adjacent notes pitch distance
for (int i = 0; i < pitches.Length - 1; i++)
{
// calculate pitch distance between the two adjacent notes
adjacentDistance = Math.Abs(pitches[i + 1] - pitches[i]);
// update relevant counters according to step size
Enum.TryParse(adjacentDistance.ToString(), out interval);
switch (interval)
{
case PitchInterval.Unison:
numOfPerfectConsonants++;
break;
case PitchInterval.MinorSecond:
case PitchInterval.MajorSecond:
numOfDissonants++;
numOfDiatonicSteps++;
break;
case PitchInterval.MinorThird:
case PitchInterval.MajorThird:
numOfChordSteps++;
numOfImperfectConsonants++;
break;
case PitchInterval.PerfectFourth:
numOfPerfectConsonants++;
break;
case PitchInterval.Tritone:
numOfTritones++;
break;
case PitchInterval.PerfectFifth:
numOfChordSteps++;
numOfPerfectConsonants++;
break;
case PitchInterval.MinorSixth:
case PitchInterval.MajorSixth:
numOfImperfectConsonants++;
break;
case PitchInterval.MinorSeventh:
case PitchInterval.MajorSeventh:
numOfDissonants++;
break;
case PitchInterval.Octave:
numOfChordSteps++;
numOfPerfectConsonants++;
break;
default:
numOfBigLeaps++;
break;
}
}
// set total number of intervals
totalNumOfIntervals = (ulong)pitches.Length - 1;
// calculate diatonic steps ratio metric
diatonicStepsMetric = numOfDiatonicSteps / totalNumOfIntervals;
// calculate chord steps ratio metric
chordStepsMetric = numOfChordSteps / totalNumOfIntervals;
// calculate chord steps ratio metric with weighted sum according to interval type
intervalTypeMetric =
((numOfPerfectConsonants * 1.0) +
(numOfImperfectConsonants * 0.8) +
(numOfDissonants * 0.6) +
(numOfTritones * 0.3) +
(numOfBigLeaps * 0.1)) / totalNumOfIntervals;
// calculate total weighted fitness according to the different metrics
fitness = (0.50 * diatonicStepsMetric) +
(0.30 * chordStepsMetric) +
(0.20 * intervalTypeMetric);
// return fitness result
return(fitness + factor);
}
