9. The system of claim 8 , wherein the biometric voice analyzer: calculates a variation bounds for producing variation vectors for the feature vectors in the feature matrix; determines a logarithmic distance for the variation vectors; and establishes a threshold based on the logarithmic distance, wherein the threshold is used to determine whether a vocal tract configuration difference for authenticating a user is within a variation bounds.
9. The system of claim 8 , wherein the biometric voice analyzer: calculates a variation bounds for producing variation vectors for the feature vectors in the feature matrix; determines a logarithmic distance for the variation vectors; and establishes a threshold based on the logarithmic distance, wherein the threshold is used to determine whether a vocal tract configuration difference for authenticating a user is within a variation bounds. 10. The system of claim 9 , wherein the biometric voice analyzer: determines a variation bounds on the personal vocal tract shape; calculates a histogram on the variation bounds; determines a maximum for the histogram; calculates a derivative vector based on the maximum; and calculates a personal histogram and second variation bounds based on the derivative vector.