Chord based random

Orchestral piece. In fact, a concerto grosso, with a few soloists (concertino) and accompaniment.

Not quite complete, should end with some coda or cadence.

The instruction:

perl  thernd.pl   rand_345     size_70     sec_8

will produce a score named,  rnd345 and a playable midi file  rnd345.mid .

The program thernd.pl :

• reads the list of all possible 4095 pitch sets, graded by dissonance.
  Dissonance is defined in the good old-fashioned way: thirds, triads are consonant, tritones and seventh chords more dissonant, curiosities such as AB♭DEG# very dissonant.

• parses the parameter list:

  rand_345

  the seed for random number generation

  size_SIZE

  a number specifying how many motifs will be played

  sec_SECLENGTH

  the minimum length of a section

• selects about SIZE pitch sets, giving preference to consonant ones.
  This is done by three methods:

  1. pick at random a pitch set, add it to the list
  2. pick at random a segment from the list, replicate it a few times in place
  3. pick at random a segment from the list, add it a few times at the end of the list

• makes motifs from the pitch sets enlisted above.
  

  A motif consists of a bass and solo. The bass is a chord, which uses 2 to 4 notes of the pitch set, with possible doubling. The solo is a melody which uses notes from the chord, with arbitrary durations.
  E.g. : the pitch set    AB♭DEG#    may become

  bass chord:	B♭,D,B♭,E
  solo melody:	B♭ 1   D 1   A 3   E 2   B♭ 2   D 8  G# 4

  Here   D 1   A 3   means: D lasting one unit, A lasting three units, etc. Usually, but not always, there are 12 or 24 units in total.

  Notice that the algorithm, although random, will produce identical motifs from identical pitch sets.

• subdivides the list of motifs into sections.
  This just inserts certain marks, indicating that at that point the instrumentation changes, and a crescendo/diminuendo starts.

• creates the score
  
  • Each motif is assigned a duration, 2/4  3/4  4/4  5/4  6/4. This generates difficult subdivisions:

    E.g., assume one fits   B♭ 1   D 1   A 3   E 2   B♭ 2   A 3   D 8   G# 4   in a   3/4   measure.
    There are 24 units in the melody, the total duration is 3/4, so the unit lasts 3/4 x 1/24 = 1/32
    The melody will be played:
      B♭ 1/32   D 1/32   A 3/32   E 1/16   B♭ 1/16   A 3/32   D 1/4   G# 1/8
    This can be still notated with the usual subdivisions, but ... what a mess!

    And then, try fitting:   B♭ 1   D 1   A 3   E 2   in a   3/4   measure.
    There are 7 units in the melody, so the unit lasts 3/4 x 1/7 = 3/28 !!
    Try to notate this rhythm – one must use septuplets, but how hard is it to play correcly ?!

    In contrast, the bass always plays quarter notes, which fit neatly into the durations 2/4  3/4  4/4  5/4  6/4. At most, sometimes the program divides 4/4 into 2, and 6/4 into 2 or 3, so there will be a few half notes and dotted half notes.

    In fact, the whole piece sounds quite tame, athough the solo melody seldom starts "on the beat", because of the subdivisions.

  • Notes are assigned register, i.e. C may be middle C or the open string viola C, etc.

  • Random instrument choice and crescendo/diminuendo are inserted at the section starts.

• Finally, the score is written as a MIDI file.