Apparatus and method for encoding and decoding information in audio signals
First Claim
1. An encoding device for encoding digital data onto audio frequency signals, said device comprising:
- means for generating, in a given band of the audio frequency, a pulse-width-modulated signal encoded with digital information;
means for identifying temporal portions of the audio frequency signal having low energy in given band and relatively high energy in a band proximally below the given band; and
means for summing said-pulse-width modulated signal and the audio frequency signal to produce an encoded audio frequency signal containing the encoded digital information in the low energy temporal portion such that human perception of the encoded audio frequency signal is substantially identical to that of the original audio frequency signal, whereinsaid encoding device encodes digital information in both first and second audio frequency channel signals of a stereo audio frequency signal, wherein said generating means generates a second pulse-width-modulated signal encoded with digital information inversely corresponding to said first pulse-width-modulated signal and said summing means adds the fist pulse-width-modulated signal to the first audio frequency channel signal and the second pulse-width-modulated signal to the second audio frequency channel signal.
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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.
540 Citations
12 Claims
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1. An encoding device for encoding digital data onto audio frequency signals, said device comprising:
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means for generating, in a given band of the audio frequency, a pulse-width-modulated signal encoded with digital information; means for identifying temporal portions of the audio frequency signal having low energy in given band and relatively high energy in a band proximally below the given band; and means for summing said-pulse-width modulated signal and the audio frequency signal to produce an encoded audio frequency signal containing the encoded digital information in the low energy temporal portion such that human perception of the encoded audio frequency signal is substantially identical to that of the original audio frequency signal, wherein said encoding device encodes digital information in both first and second audio frequency channel signals of a stereo audio frequency signal, wherein said generating means generates a second pulse-width-modulated signal encoded with digital information inversely corresponding to said first pulse-width-modulated signal and said summing means adds the fist pulse-width-modulated signal to the first audio frequency channel signal and the second pulse-width-modulated signal to the second audio frequency channel signal. - View Dependent Claims (2, 3, 4, 5)
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6. An encoding device for encoding digital data onto an audio frequency signal, said device comprising:
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means for generating a spread-spectrum signal encoded with digital information; and means for summing said spread-spectrum signal and said audio frequency signal to produce an encoded audio frequency signal containing the encoded digital information such that the perception of the encoded audio frequency signal is substantially identical to that of the original audio frequency signal, wherein said audio frequency signal is a stereo signal having first and second channel audio frequency components, said summing means comprising; means for truncating said first and second channel components to a predetermined accuracy level to obtain first and second truncated signals; means for dividing said first and second truncated signals by a maximum value of said audio frequency signal to obtain first and second divided signals; means for multiplying said first and second divided signals;
by said spread-spectrum signal to obtain first and second scaled signals;means for adding said first scaled signal to said first channel audio frequency component; and means for subtracting said second scaled signal from said second audio frequency component.
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7. A decoding device for decoding digital data encoded onto audio frequency signals, said device comprising:
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means for detecting a spread-spectrum signal encoded with digital information from an encoded audio frequency signal; means for decoding said digital information from said detected spread-spectrum signal; and means for outputting said decoded digital information in a human perceivable format, wherein said encoded audio frequency signal is a stereo signal having first and second channel encoded audio frequency components, and wherein said detecting means comprises; means for truncating said first and second channel components to a predetermined accuracy level to obtain first and second truncated signals; means for inverting said first and second truncated signals to obtain first and second inverted signals; means for multiplying said first and second inverted signals by a maximum value of said audio frequency signal to obtain first and second descaling signals; means for multiplying said first and second descaling signals by said first and second channel components to obtain first and second descaled signals; and means for subtracting said second descaled signal from said first descaled signal to obtain said spread-spectrum signal. - View Dependent Claims (8)
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9. A method for encoding digital information onto an audio frequency signal, said method comprising the steps of:
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generating a spread-spectrum signal representing the digital information, and summing the spread spectrum signal and the audio frequency signal to produce an encoded audio frequency signal containing the digital information such that human perception of the encoded analog audio frequency signal portion is substantially identical to the analog audio frequency signal, wherein said audio frequency signal is a stereo signal having first and second channel audio frequency components, said summing step comprising the steps of; truncating said first and second channel components to a predetermined accuracy level to obtain first and second truncated signals; dividing said first and second truncated signals by a maximum value of said audio frequency signal to obtain first and second divided signals; multiplying said first and second divided signals by said spread-spectrum signal to obtain first and second scaled signals; adding said first scaled signal to said first channel audio frequency component; and subtracting said second scaled signal from said second audio frequency component. - View Dependent Claims (10)
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11. A method for decoding digital data encoded onto audio frequency signals, comprising the steps of:
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detecting a spread-spectrum signal encoded with digital information from an encoded audio frequency signal; decoding said digital information from said detected spread-spectrum signal; and outputting said decoded digital information in a human perceivable format, wherein said encoded audio frequency signal is a stereo signal having first and second channel encoded audio frequency components, and wherein said detecting step comprises the steps of; truncating said first and second channel components to a predetermined accuracy level to obtain first and second truncated signals; inverting said first and second truncated signals to obtain first and second inverted signals; multiplying said first and second inverted signals by a maximum value of said audio frequency signal to obtain first and second descaling signals; multiplying said first and second descaling signals by said first and second channel components to obtain first and second descaled signals; and subtracting said second descaled signal from said first descaled signal to obtain said spread-spectrum signal. - View Dependent Claims (12)
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Specification