OpenMusic Tutorials

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Tutorial 11: Constructing a Chord with random notes from a

harmonic spectrum

Topics

Using a random functions to choose elements from a harmonic series which are then built into Chords

Key Modules Used

pitchwheel, x-append, om- random, nth-random, repeat-n, om+, Chord-seq

The Concept:

The repeat-n box evaluates the function at its first input a number of times (indicated at the second input) and returns the result as a list. The om-random box returns a random number between its two inputs. We start with the harmonic spectrum chord generated in Tutorial 8. We’ll build 5 groups of random chords from its elements, then transpose the second of the groups up by a fourth and the fourth of the groups up by a fifth, creating a sort of demented I-IV-I-V-I progression.

If you built a different harmonic series in Tutorial 8 and want to use it here, hold option and drag it into the Tutorial 11 window- this will create a copy of your original object. Note that this works with any object or group of objects.

The Patch:

nth-random (C) chooses a random note from the chord (A). This is repeated by repeat-n (E) a random number of times set by om-random (D). This will yield a list of random midics of a random length. This entire operation is itself carried out 5 times by the second repeat-n box (F). Each time it is evaluated it returns a group of 5 chords (in midics) with between 3 and 10 members.

x-append creates a list with all its inputs. In this case, all the inputs come from repeat-n. Since repeat-n produces itself produces a list, x-append will create a list of lists- what is called a tree.

The second and fourth inputs to x-append are passed through om+ (H & I) for a transposition. The others are untouched. Note that x-append has 5 inputs here- each of those inputs causes repeat-n to be evaluated anew. This means that each group of 5 chords will be different, randomly generated.

The result of x-append is a list of lists. Remember the discussion of data type in Tutorial 9? Well, the _lmidic_ input of the Chord-seq object can take either a list of integers, in which case it assumes they are individual notes to be taken in order, or a list of lists, a tree, in which case it assumes each sublist represents a chord. That is what happens here.

When you are done, you can play the Chord-seq. You may need to evaluate the pitchwheel function in the upper- right in order that the microtones play back correctly. (See Tutorial 10 for more info).

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