# What is VOIS3D?

VOIS3D is a software tool for acoustic phonetic, sociolinguistic, and experimental phonological research. VOIS3D integrates previous and new methods for vowel formant frequency normalization and duration normalization, with a new method for graphical vowel representation that allows numerical. This is possible because VOIS may take as its input either previously normalized vowel data, or raw data which may then be normalized as part of the graphing process.

**Big idea**: Normalized scatter for two vowel distributions is modeled as two best-fit ellipses oriented at angles with respect to F1, F2 axes. The output of the metric is an *overlap fraction*. The overlap fraction represents the area of the region of overlap (the region shared by both best-fit ellipses).

**Procedure**:

- 1. Each observed vowel is plotted in a coordinate system where (x,y) = (normF1, normF2)
- 2. Center each vowel class' datapoints around its own origin. (0,0) is the center of each system's vowel space. Determine the geometric formula for each ellipse and define a principal axis for each.
- 3. Rotate each ellipse along its principal axis; determine the range of coordinates it occupies within its own 2D space.
- 4. Using area information, determine extent of overlap between areas of Vowel 1 & Vowel 2. The output of this procedure is referred to as the "overlap fraction", a real-number value between 0-100%. (Wassink 1999,2006)

**Examples of Visualizations with VOIS3D:**