Harmonic adaptive speech coding method and system
First Claim
1. A method for processing an audio signal comprising the steps of:
- dividing the signal into segments, each segment representing one of a succession of time intervals;
detecting for each segment the presence of a fundamental frequency;
if such a fundamental frequency is detected, estimating the amplitudes of a set of sinusoids harmonically related to the detected fundamental frequency, the set of sinusoids being representative of the signal in the time segment; and
encoding for subsequent storage and transmission the set of the estimated harmonic amplitudes, each amplitude being normalized by the sum of all amplitudes.
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Abstract
A method and system is provided for encoding and decoding of speech signals at a low bit rate. The continuous input speech is divided into voiced and unvoiced time segments of a predetermined length. The encoder of the system uses a linear predictive coding model for the unvoiced speech segments and harmonic frequencies decomposition for the voiced speech segments. Only the magnitudes of the harmonic frequencies are determined using the discrete Fourier transform of the voiced speech segments. The decoder synthesizes voiced speech segments using the magnitudes of the transmitted harmonics and estimates the phase of each harmonic from the signal in the preceding speech segments. Unvoiced speech segments are synthesized using linear prediction coding (LPC) coefficients obtained from codebook entries for the poles of the LPC coefficient polynomial. Boundary conditions between voiced and unvoiced segments are established to insure amplitude and phase continuity for improved output speech quality.
149 Citations
52 Claims
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1. A method for processing an audio signal comprising the steps of:
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dividing the signal into segments, each segment representing one of a succession of time intervals; detecting for each segment the presence of a fundamental frequency; if such a fundamental frequency is detected, estimating the amplitudes of a set of sinusoids harmonically related to the detected fundamental frequency, the set of sinusoids being representative of the signal in the time segment; and encoding for subsequent storage and transmission the set of the estimated harmonic amplitudes, each amplitude being normalized by the sum of all amplitudes. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method for synthesizing audio signals from data packets, at least one of the data packets representing a time segment of a signal characterized by the presence of a fundamental frequency, said at least one data packet comprising a sequence of encoded amplitudes of harmonic frequencies related to the fundamental frequency, the method comprising the steps of:
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for each data packet detecting the presence of a fundamental frequency; and synthesizing an audio signal in response only to the detected fundamental frequency and the sequence of amplitudes of harmonic frequencies in said at least one data packet. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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27. A system for processing audio signals comprising:
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means for dividing an audio signal into segments, each segment representing one of a succession of time intervals; means for detecting for each segment the presence of a fundamental frequency; means for estimating the amplitudes of a set of sinusoids harmonically related to the detected fundamental frequency, the set of sinusoids being representative of the signal in the time segment; and means for encoding the set of harmonic amplitudes, each amplitude being normalized by the sum of all amplitudes. - View Dependent Claims (28, 29, 30, 31, 32, 33, 34, 35, 36, 37)
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38. A system for synthesizing audio signals from data packets, at least one of the data packets representing a time segment of a signal characterized by the presence of a fundamental frequency, said at least one data packet comprising a sequence of encoded amplitudes of harmonic frequencies related to the fundamental frequency, the system comprising:
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means for determining the fundamental frequency of the signal represented by said at least one data packet; means for synthesizing an audio signal segment in response to the determined fundamental frequency and the sequence of amplitudes of harmonic frequencies in said at least one data packet; and means for providing amplitude and phase continuity on the boundary between adjacent synthesized audio signal segments. - View Dependent Claims (39, 40, 41, 42, 43)
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44. A system for synthesizing speech from data packets, the data packets representing voiced or unvoiced speech segments, comprising:
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means for determining whether a data packet represents a voiced or unvoiced speech segment; means for synthesizing unvoiced speech in response to encoded information in an unvoiced data packet; means for synthesizing voiced speech segment signal in response only to a sequence of amplitudes of harmonic frequencies encoded in a voiced data packet; and means for providing amplitude and phase continuity on the boundary between adjacent synthesized speech segments. - View Dependent Claims (45, 46, 47)
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48. A method for processing an audio signal comprising the steps of:
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dividing the signal into segments, each segment representing one of a succession of time intervals; detecting for each segment the presence of a fundamental frequency; if such a fundamental frequency is detected, estimating the amplitudes of a set of sinusoids harmonically related to the detected fundamental frequency, the set of sinusoids being representative of the signal in the time segment; encoding for subsequent storage and transmission the set of the estimated harmonic amplitudes, each amplitude being normalized by the sum of all amplitudes; and synthesizing an audio signal in response only to the fundamental frequency and the sequence of normalized amplitudes of harmonic frequencies. - View Dependent Claims (49, 50, 51, 52)
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Specification