Watermark detection algorithms in the spread-spectrum audio watermarking systems would have optimal performance if host audio had properties of additive white Gaussian noise. However, statistical properties of the host audio signal are generally different from properties of AWGN. Therefore, there is a need for decorrelation of watermarked audio in order to achieve optimal detection based on correlation. In this paper, we describe whitening procedure for audio using Savitzky-Golay FIR filter, based on polynomial fitting of data. Residual signal has more Gaussian-like distribution and significantly smaller variance compared to the case of unprocessed watermarked audio, which was verified using two hypothesis tests for data distribution normality. The procedure considerably improves detection results and has higher resistance to various watermark attacks in comparison with standard correlation detection.