vexations in perl

control loops for serious immobility

john saylor, YAPC::NA 2005
http://or8.net/~johns/vex/

Erik Satie

• 1866-1925
• best known for Gymnopédies, 3 short piano pieces, each a sort of variation
• also wrote Furniture Music, earliest example of conscious ambient music
• scores often have extra musical text running over passages, commentary for the performer
• “rediscovered” in the 1960s

Vexations

• written 1893-ish [undated manuscript]
• consists of a melody and 2 slightly different harmonizations
• melody is chromatic and harmony is diminished
• notational grammar obfuscates pitch relationships
• john cage arranged first performance of 840 repetitions in 1963, took over 24 hours to perform

manuscript translations and notes

• “Pour se jouer 840 fois de suite ce motif, il sera bon de se préparer au préalable, et dans le plus grand silence, par des immobilités sérieuses”
• To play this motif 840 times in succession, it would be advisable to prepare oneself beforehand, in the deepest silence, by serious immobilities
• “À ce signe il sera d'usage de présenter le thème de la Basse”
• Customarily, at this sign, the theme of the bass will be presented
• note placement of ⊕ signs, indicating 5 repetitions, not 4
• tempo marking is “Très lent”, very slow

manuscript

MIDI

• Musical Instrument Digital Interface: common language between computers and digital instruments, enables notation of musical parameters as integers
• General MIDI standardized tone color to instrument number relationship
• tone colors are local to sound card, varies from card to card
• tiny file size, easy to send over network
• MIDI::Simple perl module used to generate file

requirements

• cannot simply repeat, must vary
• rate of variations should be gentle and easy to follow
• length should also be variable
• audio output should reward careful listening
• each run of program should generate something different

organization

• 3 parts: beginning middle end
• beginning and end are through composed
• middle varies in length and musical content
• middle variations proceed by different mechanisms
  • modulate up and down [within limits] repeatedly
  • per set of 5 repetitions or individual theme statement or single event
  • tied to progress through middle section
  • random events [indeterminacy]

vex: beginning

• first set of 5
  • solo piano
  • pedantic, lays out material to be varied
• second set of 5
  • tone color changes each event
  • duration gets arithmetically longer
  • velocity gets arithmetically quieter
  • moves toward silence and slowness
• beginning section sets the tone for variations to follow

vex: middle 0

• rhythm
  • tempo fluctuates gradually slower and faster
  • duration occasionally speeds up or slows down within a set
  • notes get held sporadically
• pitch
  • occasional shift in range
  • pitch substitutions get increasingly chromatic as they proceed

vex: middle 1

• sound color
  • change instrument family each set of 5
  • change within family each individual set
  • sometimes instrument family is “random”
• velocity
  • gradual fluctuation louder and softer
  • occasional punch or fall off on individual notes

vex: end

• “silent” repetition
  • breaks texture
  • gives listener aural space to reorient [and signal immanent ending]
  • looks back to gradual move toward silence in beginning
  • sideways homage to cage
• final set of 5
  • solo piano
  • matches first set
  • reviews original material

data structures

• 4 arrays
  • @cantus
  • @voice0
  • @voice1
  • @durations
• each array has the same number of elements [19]
• @cantus, @voice0, @voice1 arrays have pitch numbers
• @durations has multiplier for duration unit [1 or 2]

ex 0: longer and quieter

    $durationExtra = 0;
    $velocity = 96;
    
    for ( $c = 0; $c < scalar @cantus; $c++ )
    {
      $duration = $durations[ $c ] * 48;
      $durationExtra += 1;
      $duration += $durationExtra;
      $velocity -= 1;

      # add to midi object
    }
  

ex 1: per set changes

    $loopVar = $loop % 5;
    if ( ! $loopVar ) {
      if ( int rand ( 7 ) ) {
        if ( int rand ( 11 ) ) {
          $randomInstrument = 0; $patch = &pickInstrument ( $loop );
        } else {
          $randomInstrument = 1; $patch = &pickInstrument ( );
        }
      }
      if ( int rand ( 5 ) ) {
        &modifyParam ( $tempoData );
        $midi→set_tempo  ( int ( 60_000_000 / $tempoData→{modified} ) );
        $tempoData→{current} = delete $tempoData→{modified};
      }
    }
  

ex 2: &modifyPitch

    # $transVal = &modifyPitch ( $startVal, $intervalOffset, $range )
    sub modifyPitch {
      my $octaveDivisions = sprintf ( "%d", 12 / $intervalOffset );
      my $rndLimit = $octaveDivisions * $range;
      my $rnd = int rand ( $rndLimit );
      my $offset = $rnd - ( int ( $rndLimit / 2 ) );
      
      # back to half steps
      $offset *= sprintf ( "%d", 12 / $octaveDivisions );
      my $transVal = $startVal + $offset;
      return $transVal % 128;
    }
  

ex 3: &modifyParam

    # $hr = &modifyParam ( $hr )
    sub modifyParam {
      my $rndLimit = sprintf ( "%d", $hr→{current} * $hr→{range} );
      my $offset = int rand ( $rndLimit );
      if ( $hr→{direction} < 0 ) { $offset *= -1; }
      my $modified = $hr→{current} + $offset;
      if ( $modified < $hr→{min} ) {
        $modified = $hr→{min}; $hr→{direction} = 1;
      } elsif ( $modified > $hr→{max} ) {
        $modified = $hr→{max}; $hr→{direction} = -1;
      }
      $hr→{modified} = $modified;
      return $modified;
    }
  

aesthetic issues

• since script outputs different file each time it is run, what is the identity of the art work?
• musical variations explore relationship between repetition and change
• long time frame of musical output creates different scale of change
• programmer as artist, working with data structures instead of pitches and rhythms [colors, words, …]
• historical context: what has been added/changed from satie's score?

auxillary material

• web vex
  • http://or8.net/~johns/cgi-bin/vex.pl
  • web interface to script
  • number of repetitions entered on web form
  • can be downloaded to browser or as file
• MIDI realization
• perl script used to generate output [downloads as text file to fool webserver]