  OpenMusic DocumentationOM 6.6 User Manual > Score Objects > 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. Time signature = n // n   or ( n n ). It must be specified at each new measure, even if it remains unchanged.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.
Parenthesis Levels
 A rhythm tree has at least three levels of parenthesis : number of measureslist of measurestime 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 groups , 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. page précédentepage suivante
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