A method, an apparatus and a computer program product for adaptive, content-based watermark embedding of a digital audio signal (100) are disclosed. Corresponding watermark extracting techniques are also disclosed. Watermark information (102) is encrypted (120) using an audio digest signal, i.e. a watermark key (108). To optimally balance inaudibility and robustness when embedding and extracting watermarks (450), the original audio signal (100) is divided into fixed-length frames (1100, 1120, 1130) in the time domain. Echoes (S'[n], S''[n]) are embedded in the original audio signal (100) to represent the watermark (450). The watermark (450) is generated by delaying and scaling the original audio signal (100) and embedding it in the audio signal (100). An embedding scheme (104) is designed for each frame (1100, 1120, 1130) according to its properties in the frequency domain. Finally, a multiple-echo hopping module (160) is used to embed and extract watermarks in the frame (1100, 1120, 1130) of the audio signal (100). An audio watermarking system known as KentMark(Audio) is implemented.