Method and apparatus for transmitting watermark data bits using a spread spectrum, and for regaining watermark data bits embedded in a spread spectrum

Spread spectrum technology and the related inserted or added information signal can be used for implementing watermarking digital audio signals. A known processing for retrieving at receiver or decoder side the watermark signal information bit from the spread spectrum is convolving the received or replayed spectrum with a spreading function that is time-inverse with respect to the original spreading function. If BPSK modulation was used for applying the spread spectrum function, the output is a peak at the middle of the sequence of correlation values, the sign of such peak representing the value of the desired watermark signal information bit. According to the invention, in order to cope with echo distortions, two or more orthogonal spreading sequences are used at encoder side with the original or encoded audio signal in baseband. When applying the corresponding time-inverse orthogonal spreading sequences at decoder side, echoes that are longer than each one of spreading sequence's lengths can be fully removed. The spreading sequences applied can be modified at decoder side according to estimated echo delay values.