Abstract: A method and apparatus encodes and decodes machine readable signals in audio signals for producing humanly perceived audio transmissions. The encoding device includes circuitry for identifying portions of the audio signal having relatively low energy in a given band and relatively high energy in a band proximally below the given band. The machine readable signals are then inserted into the identified portions of the audio signal. According to another embodiment, the machine readable signals are encoded as a spread-spectrum signal which is added to the original audio signal. The spread-spectrum signal is scaled using a unique technique referred to as Common Mode Scaling.

Abstract: Apparatus and methods are provided for encoding, storing and decoding auxiliary information on an analog source signal in a way which has minimal impact on the human perception of the source information when the source signal is applied to an appropriate output device, such as a speaker or a display monitor. The autocorrelation function of a host signal is modulated according to the value of an auxiliary information signal by adding a host modifying signal to the host signal. The auxiliary signal is decoded by generating the autocorrelation function of the encoded signal and extracting the auxiliary signal according to well-known signal extraction techniques.

Abstract: A method and apparatus for encoding information symbols onto an analog host signal modifies signal peaks of the host signal to fall within predetermined amplitude bands. A set of symbols is defined wherein each symbol corresponds to a defined number of signal peaks or to a particular value of signal peak within a band. An additional information channel may be created by altering polarity changes of signal peaks in accordance with predetermined polarity sequences to represent a second set of defined symbols.

Abstract: A method and apparatus encodes and decodes machine readable signals in audio signals for producing humanly perceived audio transmissions. The encoding device includes circuitry for identifying portions of the audio signal having relatively low energy in a given band and relatively high energy in a band proximally below the given band. The machine readable signals are then inserted into the identified portions of the audio signal. According to another embodiment, the machine readable signals are encoded as a spread-spectrum signal which is added to the original audio signal. The spread-spectrum signal is scaled using a unique technique referred to as Common Mode Scaling.