A method for a machine or group of machines to watermark speech audio transmissions includes receiving a speech audio signal, receiving a watermark signal including a message of multiple bits, each bit having one of two values, each value represented by one of two symbols, each of the symbols corresponding to a respective audio segment, and at a time t1, transmitting a first transmission including at least some of the multiple bits in multiple spectral channels of the speech audio signal, each spectral channel corresponding to a different frequency range, wherein a first one of the multiple spectral channels carries a first bit from the multiple bits while at the same time a second one of the multiple spectral channels carries a second bit from the multiple bits different from the first bit.