A method of searching for an interpolated peak of a Normalized Correlation Square (NCS) signal derived from an audio signal, comprises: producing quadratically interpolated correlation (QIC) signal values at interpolated time lags; squaring each of the QIC signal values to produce square QIC signal values; producing an individual interpolated energy signal value corresponding to each of the square QIC signal values, wherein ratios of the square QIC signal values to their corresponding interpolated energy values represent interpolated NCS signal values; and selecting, as the interpolated peak, a largest interpolated NCS signal value among the interpolated NCS signal values without evaluating the ratios.