Embedded signalling
First Claim
1. A method of embedding a sequence of code symbols in an audio signal, said method comprising:
- generating a code signal representing the sequence of code symbols and with frequency components essentially confined to a preselected signalling band lying within the bandwidth of said audio signal;
continuously frequency analyzing said audio signal over a frequency band encompassing said signalling band;
dynamically filtering said code signal as a function of said analysis thereby to provide a modified code signal with frequency component levels which, at each time instant, are essentially negligibly small outside said signalling band and, at each frequency within said signalling band, are essentially a preselected proportion of the levels of the audio signal frequency components in a corresponding frequency range; and
combining said modified code signal with said audio signal thereby to provide a composite audio signal.
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Accused Products
Abstract
A code signal representing a sequence of code symbols carrying digital information is generated with the frequency components of the code signal being essentially confined to a preselected signalling band lying within the bandwidth of an audio signal within which the code signal is to be embedded. The audio signal is continuously frequency analyzed over a frequency band encompassing the signalling band and the code signal is dynamically filtered as a function of the analysis thereby to provide a modified code signal with frequency components which are, at each time instant, essentially a preselected small proportion of the levels of the corresponding audio signal frequency components. Accordingly, the modified code signal can be combined with the audio signal to obtain a composite audio signal which is not readily distinguishable from the original audio signal by listening. Furthermore, the digital information can be recovered from the composite audio signal by a procedure which is essentially the compliment of that used to obtain the composite audio signal.
941 Citations
25 Claims
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1. A method of embedding a sequence of code symbols in an audio signal, said method comprising:
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generating a code signal representing the sequence of code symbols and with frequency components essentially confined to a preselected signalling band lying within the bandwidth of said audio signal; continuously frequency analyzing said audio signal over a frequency band encompassing said signalling band; dynamically filtering said code signal as a function of said analysis thereby to provide a modified code signal with frequency component levels which, at each time instant, are essentially negligibly small outside said signalling band and, at each frequency within said signalling band, are essentially a preselected proportion of the levels of the audio signal frequency components in a corresponding frequency range; and combining said modified code signal with said audio signal thereby to provide a composite audio signal. - View Dependent Claims (2)
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3. A method of detecting a sequence of predetermined code symbols which is represented by a code signal embedded in a composite audio signal, said method comprising:
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continuously frequency analyzing said composite audio signal over a frequency band encompassing a preselected signalling band lying within the bandwidth of said composite audio signal; within said signalling band, filtering said composite audio signal as a converse function of the analysis thereby to provide an essentially even energy distribution over said signalling band; and applying said filtered signal to a set of filters, each filter in said set being matched to one of said code symbols.
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4. A method of transmitting a sequence of code symbols over a channel carrying an audio signal, said method comprising:
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generating a code signal representing the sequence of code symbols and with frequency components essentially confined to a preselected signalling band lying within the bandwidth of said audio signal; continuously frequency analyzing said audio signal over a frequency band encompassing said signalling band; dynamically filtering said code signal as a function of said analysis thereby to provide a modified code signal with frequency component levels which are, at each time instant, essentially negligibly small outside said signalling band and, at each frequency within said signalling band, essentially a preselected proportion of the levels of the audio signal frequency components in a corresponding frequency range; combining said modified code signal with said audio signal thereby to provide a composite audio signal and transmitting said composite audio signal over said channel; continuously frequency analyzing the received composite audio signal over a frequency band encompassing said preselected signalling band; within said signalling band, filtering said received composite audio signal as a converse function of the analysis thereby to provide an essentially even energy distribution over said signalling band; and applying said filtered signal to a set of filters, each filter in said set being matched to one of the code symbols. - View Dependent Claims (5, 6, 7, 8, 9)
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10. A method of embedding a sequence of code symbols in an audio signal, said method comprising:
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for each symbol input, generating a corresponding pseudorandom sequence representing the respective symbol; upsampling, filtering and transposing said code sequences thereby to generate a code signal having frequency components essentially confined to a preselected signalling band lying within the bandwidth of said audio signal; continuously frequency analyzing said audio signal over a frequency band encompassing said signalling band; dynamically filtering said code signal as a function of said analysis thereby to provide a modified code signal with frequency component levels which are at each time instant essentially a preselected proportion of the levels of the audio signal frequency components in a corresponding frequency range; combining said modified code signal with said audio signal thereby to provide a composite audio signal.
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11. A method of transmitting a sequence of code symbols selectable from a predetermined alphabet and occurring at a rate of about 4.3 per second over a channel carrying an audio signal having a bandwidth in the order of 20 k HZ, said method comprising:
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generating a code signal representing the sequence of code symbols and having frequency components essentially confined to a preselected signalling band having a bandwidth of about 8800 Hz centered on a frequency of about 6300 Hz; continuously frequency analyzing said audio signal over a frequency band encompassing said signalling band;
dynamically filtering said code signal as a function of said analysis thereby to provide a modified code signal with frequency component levels which are, at each time instant, essentially negligibly small outside said signalling band and, at each frequency within said signalling band, essentially a preselected proportion of the levels of the audio signal frequency components in a corresponding frequency range, said preselected proportion representing a modified code signal level which is about 19 dB below the level of said audio signal;combining said modified code signal with said audio signal thereby to provide a composite audio signal and transmitting said composite audio signal over said channel; continuously frequency analyzing the received composite audio signal over a frequency band encompassing said preselected signalling band; within said signalling band, filtering said received composite audio signal as a converse function of the analysis thereby to provide an essentially even energy distribution over said signalling band; and applying said filtered signal to a set of filters, each filter in said set being matched to one of said code symbols. - View Dependent Claims (12)
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13. A method of communicating code symbols over a channel carrying an audio signal, said method comprising:
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for each symbol input, generating a corresponding pseudorandom sequence baseband signal representing the respective symbol;
filtering and transposing upward in frequency said pseudorandom sequences thereby to generate a code signal having frequency components essentially confined to a preselected signalling band lying within the bandwidth of said audio signal;continuously frequency analyzing said audio signal over a frequency band encompassing said signalling band; dynamically filtering said code signal as a function of said analysis thereby to provide a modified code signal with frequency component levels which are, at each time instant and at each frequency within said signalling band, essentially a preselected proportion of the levels of the audio signal frequency components in a corresponding frequency range; combining said modified code signal with said audio signal thereby to provide a composite audio signal and transmitting said composite audio signal over said channel; continuously frequency analyzing the received composite audio signal over a frequency band encompassing said preselected signalling band; within said signalling band, filtering said received composite audio signal as a converse function of the analysis thereby to provide an essentially even energy distribution over said signalling band; transposing components in said signalling band downward in frequency to obtain a received baseband signal; and applying said received baseband signal to a set of filters, each filter in said set being matched to one of the pseudorandom sequences representing symbols.
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14. Apparatus for combining a sequence of code symbols with an audio signal, said apparatus comprising:
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means for generating a corresponding code signal representing the sequence of code symbols, said code signal comprising frequency components essentially confined to a preselected signalling band lying within the bandwidth of said audio signal; means for continuously frequency analyzing said audio signal over a frequency band encompassing said signalling band; dynamic filter means for selectively filtering said code signal as a function of said analysis thereby to provide a modified code signal with frequency component levels which are, at each time instant, essentially negligibly small outside said signalling band and, at each frequency within said signalling band, are essentially a preselected proportion of the levels of the audio signal frequency components in a corresponding frequency range; and means for combining said modified code signal with said audio signal thereby to provide a composite audio signal. - View Dependent Claims (15, 16, 17, 18)
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19. Apparatus for extracting a sequence of code symbols which are represented by respective pseudorandom sequences embedded in a composite audio signal, said apparatus comprising:
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means for continuously frequency analyzing said composite audio signal over a frequency band encompassing a preselected signalling band lying within the bandwidth of the composite audio signal; dynamic filtering means for selectively filtering said composite audio signal within said signalling band as a converse function of said analysis thereby to provide a modified audio signal having an essentially even energy distribution over said signalling band; and a set of matched filters responsive to said modified signal, each filter in said set being matched to one of the pseudorandom sequences representing said symbols.
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20. Apparatus for combining a sequence of code symbols occurring at a rate of about 4.3 per second with an audio signal having a bandwidth in the order of 20 k HZ, said apparatus comprising:
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means for generating a corresponding code signal representing the sequence of code symbols, said code signal comprising frequency components essentially confined to a preselected signalling band having a bandwidth of about 8800 Hz centered on a frequency of about 6300 Hz; means for continuously frequency analyzing said audio signal over a frequency band encompassing said signalling band; dynamic filter means for selectively filtering said code signal as a function of said analysis thereby to provide a modified code signal with frequency component levels which are, at each time instant, essentially negligibly small outside said signalling band and, at each frequency within said signalling band, are essentially a preselected proportion of the levels of the audio signal frequency components in a corresponding frequency range, said preselected proportion representing a modified code signal level which is about 19 dB below the level of said audio signal; and means for combining said modified code signal with said audio signal thereby to provide a composite audio signal.
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21. Apparatus for combining a sequence of code symbols with an audio signal, said apparatus comprising:
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means for generating a corresponding binary code sequence representing each successive symbol; means for filtering and transposing information bearing frequency components of said code sequences thereby to generate a code signal having frequency components essentially confined to a preselected signalling band lying within the bandwidth of said audio signal; means for continuously frequency analyzing said audio signal over a frequency band encompassing said signalling band; dynamic filter means for selectively filtering said code signal as a function of said analysis thereby to provide a modified code signal with frequency component levels which are, at each time instant, essentially a preselected proportion of the levels of the audio signal frequency components in a corresponding frequency range; means for combining said modified code signal with said audio signal thereby to provide a composite audio signal. - View Dependent Claims (22)
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23. An audio recording comprising a medium carrying a composite signal which is a mixture of an audio signal and a dynamically modified code signal representing a sequence of code symbols wherein said dynamically modified code signal is obtained by:
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generating a code signal representing the sequence of symbols with frequency components essentially confined to a preselected signalling band lying within the bandwidth of said audio signal; continuously frequency analyzing said audio signal over a frequency band encompassing said signalling band; dynamically filtering said code signal as a function of said analysis thereby to provide a modified code signal with frequency component levels which are, at each time instant, essentially negligibly small outside said signalling band and, at each frequency within said signalling band, are essentially a preselected proportion of the levels of the audio signal frequency components in a corresponding frequency range; combining said modified code signal with said audio signal thereby to provide a composite audio signal.
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24. An audio recording comprising a medium carrying a composite signal which is a mixture of an audio signal having a bandwidth in the order of 20 k Hz and a dynamically modified code signal representing a sequence of code symbols wherein said dynamically modified code signal is obtained by:
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generating a corresponding code signal representing the sequence of code symbols with frequency components essentially confined to a preselected signalling band having a bandwidth of about 8800 Hz centered on a frequency of about 6300 Hz; continuously frequency analyzing said audio signal over a frequency band encompassing said signalling band; dynamically filtering said code signal as a function of said analysis thereby to provide a modified code signal with frequency component levels which are, at each time instant, essentially negligibly small outside said signalling band and, at each frequency within said signalling band, are essentially a preselected proportion of the levels of the audio signal frequency components in a corresponding frequency range, said preselected proportion representing a modified code signal level which is about 19 dB below the level of said audio signal; combining said modified code signal with said audio signal thereby to provide a composite audio signal. - View Dependent Claims (25)
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Specification