That means the additional data has to be embedded into the speech signal. Such watermarking systems are used e.g. for CD-audio copyright protection, where copyright data is embedded into the music without any audible distortion. Current approaches such as spread spectrum watermarking, quantization index modulation, and echo hiding are presented. A system for speech watermarking in an air traffic control environment is developed. The system uses spread spectrum technology with linear prediction for spectral shaping of the watermark to achieve perceptual hiding. Error control coding is done using the BCH-code, which can both detect and correct errors. Results show that, for 12 bits/s, the watermark can be transmitted at a level which is hardly audible with very low error rate (? 0.1%). For the transmission of 24 and 36 bits/s the watermark level has to be increased to an audible but not annoying level so as to stay in a low error rate region.
Speech Watermarking for Air Traffic Control
The Air Traffic Control Voice Communication, it is desirable to transmit additional aircraft identification data over the analogue VHF voice channel.