Aerial Acoustic Modem with Decoding Capabilities Using a CELP-Based Speech Encoder

A technology for aerial transmission of acoustic data which is robust against background noise in reverberant spaces is proposed. Hidden data are encoded as complex tones whose fundamental frequencies correspond to the chromatic scale. The decoding of hidden data is based on a pitch extraction algorithm that is employed in a CELP-based speech codec. Computer simulations revealed that the average bit detection error rates can be lower than 0.1 even at 5 dB SNR and under reverberant conditions. Although at the present stage the encoded sound is random rather than melodious, imposing restrictions on the selected frequencies for the chords on the basis of the theory of harmony can enhance the melodic and harmonic features of the encoded sound.