Real-Time Pitch Spelling Using the Spiral Array

This article describes and presents a real-time bootstrapping algorithm for pitch spelling based on the Spiral Array Model (Chew 2000). Pitch spelling is the process of assigning appropriate pitch names that are consistent with the key context of numeric representations of pitch, such as MIDI or pitch class numbers. The Spiral Array Model is a spatial model for representing pitch relations in the tonal system. It has been shown to be an effective tool for tracking evolving key contexts (Chew 2001, 2002). Our pitch-spelling method derives primarily from a twopart process consisting of the determining of context-defining windows and pitch-name assignment using the Spiral Array. The method assigns the appropriate pitch names without having to first ascertain the key. The Spiral Array Model clusters together closely related pitches and summarizes note content by spatial points in the interior of the structure. These interior points, called centers of effect (CEs), approximate and track the key context for the purpose of pitch spelling. The appropriate letter name is assigned to each pitch through a nearestneighbor search in the Spiral Array space. The algorithms use windows of varying sizes for determining local and long-term tonal contexts using the Spiral Array Model.