Traditional watermarking methods based on spectrum manipulation use watermark bit as a colored noise. However, those methods show poor robustness for filtering and audio compression because of only a few spectrum coefficients being modified. In this paper, we propose a new algorithm for robust audio watermarking by using spectrum warping. Our watermark-embedding scheme is not based on spectrum coefficient manipulation, but based on warping spectrum that shifts a block of spectrum coefficients nonlinearly. The host audio signal is divided appropriately into small segments and then a non-orthogonal transform, such as bi-linear transform, is used for each segment to embed as well as to extract watermarks. Because the proposed scheme uses small segment length, we can afford to embed signature information many times into audio signal without severe degradation of SNR. Our multiple embedding scheme increases robustness against abnormal distortion of watermarked signal and has no bit error rate in MPEG1 Layer-3 128 kbps and 96 kbps compression as well as low/high pass filtering.