Patent ID: 7236927

Claim:
A method of searching for an interpolated peak of a Normalized Correlation Square (NCS) signal derived from an audio signal, the NCS signal being represented as a first ratio of a correlation square signal c 2 (k) to an energy signal E(k), where k represents time lags spanning a range of integer k-values, the interpolated peak being near a known local peak c 2 (k p )/E(k p ) of the NCS signal, comprising: (a) producing quadratically interpolated correlation (QIC) signal values (ci) at interpolated time lags between time lag k p and an adjacent time lag; (b) squaring each of the QIC signal values to produce square QIC signal values (ci 2 ); (c) producing an individual interpolated energy signal value (ei) corresponding to each of the square QIC signal values, wherein second ratios of the square QIC signal values (ci 2 ) to their corresponding interpolated energy values (ei) represent interpolated NCS signal values; and (d) selecting, as the interpolated peak, a largest interpolated NCS signal value among the interpolated NCS signal values without evaluating the second ratios.