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OM 6.4 – User ManualScore Objects > Classes > Rhythm Trees > Rhythm Trees Structure
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Rhythm Trees Structure

Traditionally, rhythm is broken up into several data : meter, measure(s) and duration(s). Rhythm trees must enclose these information in lists and sub list.

This elementary rhythm :

can be expressed as follows :

  • ( ? ( (4//4 (1 1 1 1) ) ) )
  • ( ? ( ( (4 4) (1 1 1 1) ) ) )

    A tree structure can be reduced to a list : (D (S)).

    Main Components : Duration and Subdivisions

    • D = a duration , or number of measures : ( ? ) or a number ( n ).

      When D = ?, OM calculates the duration.

      By default, this duration is equal to 1.

    • S = subdivisions (S) of this duration, that is a time signature and rhythmic proportions.

      1. Time signature = n // n   or ( n n ).

        It must be specified at each new measure, even if it remains unchanged.

      2. Rhythm = proportions : ( n n n n )

    Here, the (1 1 1 1) sub list represents four equal subdivisions of a 4/4 measure. OM calculated that the tree has two measures.
    Here, the (1 1 1 1) sub list represents four equal subdivisions of a 4/4 measure. OM calculated that the tree has two measures.
    Parenthesis Levels

    A rhythm tree has at least three levels of parenthesis :

    1. number of measures

    2. list of measures

    3. time signature and proportions.

      Note that different rhythm trees with equal proportional structures produce the same rhythmic result :

      ( 1 1 1 1) = (2 2 2 2) = (124 124 124 124)

    Durations

    Manipulating Durations

    By default, the duration of a measure is equal to 1. 1 represents the global measurement unit traditionally expressed by the time signature, such as : 4/4, 2/2  = ,  3/8 = etc.

    Changing this value multiplies or divides all the durations by a given coefficient.

    Subdivisions : Measures and Groups

    Measures

    Trees define the way measures are split into proportional durations.

    The following rhythm :

    is written : ( ? ( (4//4 (1 2 1) ) ) ) .

    Groups

    Trees also define internal subdivisions, or groups1 , within a measure.

    The following rhythm :

    is written : ( ? ( (4//4 (1 ( 2 (1 1 1) ) 1) ) ) ) .

    Writing Groups

    Note that groups must be written with a new subordinate level of parenthesis.

    1. Group

      An internal subdivision, that is, a list of proportions within a measure. A group can enclose a sub group. Basic examples are tuplets, groups of eighth, sixteenth notes. Groups of quarter, semibreves, whole notes or any other values are also admitted in rhythm trees.

      For instance :

      (? ((4//4 ( (2 ( 1 1)) (1 ( 1 (1 (1 1 1)))) (1 (1 1 1 1 1)) )))).

      This one measure tree has one group – two quarter notes – , one group with a sub group – one eighth note and a sixteenth notes triplet, and a last group – a quintuplet.

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