10. An apparatus for measuring the resemblance between sound samples, comprising: a digital acquisition and pre-processing module which converts an analog sound sample into a digital signal; an acoustic analysis module which transforms the digital signal into a vector signal composed of acoustic parameters; a covariance matrix module which computes a covariance of the acoustic vector signal at the output of the acoustic analysis module; a matrix inversion module for calculating the inverse of the symmetric matrix at the output of the covariance matrix module; a module for storing the output of the matrix inversion module in a dictionary, the storing module being only active during a training phase; a matrix multiplication module which takes during a test phase, the covariance matrix at the output of the covariance matrix module and multiplies it with an inverse covariance matrix from the dictionary, the matrix multiplication module being active only during the test phase; a module for extracting eigenvalues of the product obtained at the output of the matrix multiplication module, the extracting module being active only during the test phase; and a module for calculating a resemblance signal as a sphericity function of the eigenvalues produced by module using at least two of the following equations: ##EQU22## where a, g, and h represent respectively an arithmetic, geometrical, and harmonic mean values of the eigenvalues .lambda.k.
10. An apparatus for measuring the resemblance between sound samples, comprising: a digital acquisition and pre-processing module which converts an analog sound sample into a digital signal; an acoustic analysis module which transforms the digital signal into a vector signal composed of acoustic parameters; a covariance matrix module which computes a covariance of the acoustic vector signal at the output of the acoustic analysis module; a matrix inversion module for calculating the inverse of the symmetric matrix at the output of the covariance matrix module; a module for storing the output of the matrix inversion module in a dictionary, the storing module being only active during a training phase; a matrix multiplication module which takes during a test phase, the covariance matrix at the output of the covariance matrix module and multiplies it with an inverse covariance matrix from the dictionary, the matrix multiplication module being active only during the test phase; a module for extracting eigenvalues of the product obtained at the output of the matrix multiplication module, the extracting module being active only during the test phase; and a module for calculating a resemblance signal as a sphericity function of the eigenvalues produced by module using at least two of the following equations: ##EQU22## where a, g, and h represent respectively an arithmetic, geometrical, and harmonic mean values of the eigenvalues .lambda.k. 11. An apparatus according to claim 10, wherein the module for extracting the eigenvalues is replaced by at least two of the three following modules; a module for calculating a trace of the output of the matrix multiplication module, in parallel with; a module for calculating a determinant of the output of the matrix multiplication module, in parallel with; a module for inverting the output of the matrix multiplication module followed by a module for calculating the trace of the thus obtained matrix; wherein the module for calculating a resemblance signal calculates the resemblance signal from outputs of at least two of the three modules including the module for calculating the trace of the matrix product, the module for calculating the determinant of the matrix product, and the module for calculating the trace of the inverted matrix product.