Apparatus and methods for including codes in audio signals

A method for including a code having a plurality of code frequency components with an audio signal having a plurality of audio signal frequency components, the plurality of code frequency components including a first code frequency component having a first frequency and a second code frequency component having a second frequency different from the first frequency, comprising the steps of

• evaluating a masking ability of at least one of the plurality of audio signal frequency components to mask a code frequency component having the first frequency to human hearing to produce a first respective masking evaluation;
• evaluating a masking ability of at least one of the plurality of audio signal frequency components to mask a code frequency component having the second frequency to human hearing to produce a second respective masking evaluation;
• assigning a respective amplitude to the first code frequency component based on the first respective masking evaluation and a respective amplitude to the second code frequency component based on the second respective masking evaluation;
• and
• including the plurality of code frequency components with the audio signal.

An apparatus for including a code having a plurality of code frequency components with an audio signal having a plurality of audio signal frequency components, the plurality of code frequency components including a first code frequency component having a first frequency and a second code frequency component having a second frequency different from the first frequency, comprising:

• a digital computer having an input for receiving the audio signal, the digital computer being programmed to evaluate a masking ability of at least one of the plurality of audio signal frequency components to mask a code frequency component having the first frequency to human hearing to produce a first respective masking evaluation and to evaluate a masking ability of at least one of the plurality of audio signal frequency components to mask a code frequency component having the second frequency to human hearing to produce a second respective masking evaluation;
• the digital computer being further programmed to assign a corresponding amplitude to the first code frequency component based on the first respective masking evaluation and to assign a corresponding amplitude to the second code frequency component based on the second respective masking evaluation;
• the digital computer being programmed to produce the code as a plurality of code frequency component sets, each of the code frequency component sets representing a respectively different code symbol and including a plurality of respectively different code frequency components, the code frequency components of the code frequency component sets forming component clusters spaced from one another within the frequency domain, each of the component clusters having a respective predetermined frequency range and consisting of one frequency component from each of the code frequency component sets falling within its respective predetermined frequency range, component clusters which are adjacent within the frequency domain being separated by respective frequency amounts, and wherein the predetermined frequency range of each respective component cluster is smaller than the frequency amounts separating the respective component cluster from its adjacent component clusters;
• and means for including the plurality of code frequency components with the audio signal.

An apparatus for including a code having a plurality of code frequency components with an audio signal having a plurality of audio signal frequency components, the plurality of code frequency components including a first code frequency component having a first frequency and a second code frequency component having a second frequency different from the first frequency, comprising:

• a digital computer having an input for receiving the audio signal, the digital computer being programmed to evaluate a masking ability of at least one of the plurality of audio signal frequency components to mask a code frequency component having the first frequency to human hearing by detecting a signal power of audio signal frequency components within a specified frequency range, to determine first and second masking factors with respect to the code frequency component having the first frequency on the conditions that the signal power is at each of first and second frequencies, respectively, within the specified frequency range, the second frequency being different than the first frequency, and to select that one of the first and second masking factors which represents a smaller amplitude of the at least one code frequency component to produce a first respective masking evaluation;
• the digital computer being programmed to evaluate a masking ability of at least one of the plurality of audio signal frequency components to mask a code frequency component having the second frequency to human hearing to produce a second respective masking evaluation;
• the digital computer being further programmed to assign a corresponding amplitude to the first code frequency component based or the first respective masking evaluation and to assign a corresponding amplitude to the second code frequency component based on the second respective masking evaluation;
• and
• means for including the plurality of code frequency components with the audio signal.