This article focuses on learning the hierarchical structure of what we call a “temporal scenario” (for instance, a chord progression) to perform automatic improvisation consistently over several different time scales. We first present a way to represent hierarchical structures with a phrase structure grammar. Such a grammar enables us to analyze a scenario at several levels of organization, creating a “multilevel scenario.” We then develop a method to automatically induce this grammar from a corpus, based on sequence selection with mutual information. We applied this method to a corpus of transcribed improvisations based on the chord sequence, also with chord substitutions, from George Gershwin's “I Got Rhythm.” From these we obtained multilevel scenarios similar to the analyses performed by professional musicians. We then present a novel heuristic approach, exploiting the multilevel structure of a scenario to guide the improvisation with anticipatory behavior in an improvisation paradigm driven by a factor oracle. This method ensures consistency of the improvisation with regard to the global form, and it opens up possibilities when playing on chords that do not exist in memory. This system was evaluated by professional improvisers during listening sessions and received excellent feedback.

中文翻译：

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学习指导即兴的分层时间结构

本文侧重于学习我们称为“时间场景”（例如，和弦进行）的层次结构，以在几个不同的时间尺度上一致地执行自动即兴创作。我们首先提出了一种用短语结构语法表示层次结构的方法。这样的语法使我们能够在多个组织级别上分析场景，从而创建“多级场景”。然后，我们开发了一种方法，基于具有互信息的序列选择，从语料库中自动归纳出这种语法。我们将这种方法应用于基于和弦序列的转录即兴语料库，也带有和弦替换，来自乔治·格什温的“我有节奏”。从这些我们获得了类似于专业音乐家进行的分析的多层次场景。然后，我们提出了一种新颖的启发式方法，利用场景的多级结构来指导由因子预言机驱动的即兴范式中的预期行为的即兴创作。这种方法确保了即兴演奏与全局形式的一致性，并在演奏记忆中不存在的和弦时开辟了可能性。该系统由专业的即兴演奏者在聆听过程中进行评估，并获得了极好的反馈。