Normalized Pairwise Variability Index

Returns the Normalized Pairwise Variability Index (NPVI) and Coef. of Variation (Grabe & Low, 2002).

GETNPVI Calculates Normalized Pairwise Variability Index (NPVI) and Coefficient of Variation (CV) as described by Grabe & Low (2002).

[NPVI CV] = GETNPVI(IN) returns the Normalized Pairwise Variability
Index NPVI (M*N or M*N*P) and Coefficient of Variation CV (M*N or M*N*P) for input statement IN. IN is a matrix of syllable durations of size
M*N or M*N*P.

Example: If IN = [1 2 3; 3 3 6; 4 6 8; 4 7 7];
then [npvi cv] = getNPVI(IN) is npvi = [53.3333; 33.3333; 34.2857; 27.2727].
cv is [0.5000; 0.4330; 0.3333; 0.2887]

Example: If IN(:,:,1) = [1 2 3; 3 3 6] and IN(:,:,2) = [4 6 8; 4 7 7]
then [npvi cv] = getNPVI(IN) is npvi(:,:,1) = [53.3333; 33.3333], and
npvi(:,:,2) = [34.2857; 27.2727]. cv(:,:,1) = [0.5000; 0.4330], and
cv(:,:,2) = [0.3333; 0.2887].

See also: http://vesicle.nsi.edu/users/patel/npvi_calculator.html

Grabe, E., & Low, E. L. (2002). Durational variability in speech and the rhythm class hypothesis. In C. Gussenhoven & N. Warner (Eds.),
Papers in laboratory psychology (pp. 515–546). Cambridge University Press.