Voice band expander and expansion method, and voice communication apparatus
First Claim
Patent Images
1. A voice band expander for expanding a frequency band of an input voice signal with a frequency spectrum limited to frequencies below an upper limit, the voice band expander comprising:
- a reduced signal generator for generating, from the input voice signal, a reduced signal with a modified frequency spectrum in which magnitudes of the frequencies in the entire frequency spectrum of the input voice signal are reduced;
a band expanding signal generator for generating, from the reduced signal, a band expanding signal having a frequency spectrum in a band higher than the upper limit of the limited band of the input voice signal; and
a band expanded signal generator for combining the input voice signal and the band expanding signal, thereby to form a band expanded signal with an expanded frequency band, whereinthe reduced signal generator reduces the frequency spectral envelope and the harmonic structure of the input voice signal, the reduced signal generator comprising;
a linear predictive coding (LPC) analyzer for carrying out an LPC analysis of the input voice signal;
an LPC filter for reducing the frequency spectral envelope of the input voice signal by using LPC coefficients obtained by the LPC analyzer;
a pitch analyzer, responsive to the output of the LPC filter, for determining a pitch and pitch intensity of the input voice signal; and
a pitch filter for reducing the harmonic structure of the input voice signal according to the pitch and pitch intensity obtained by the pitch analyzer.
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Abstract
A band-limited voice signal is processed to reduce its spectral envelope or harmonic structure, or both. The resulting reduced signal is moved into a frequency band above the upper limit frequency of the band-limited voice signal, and then combined with the band-limited voice signal to form a band expanded signal with improved quality and comprehensibility, free of unnatural high-frequency resonances and unnaturally strong high-frequency harmonics.
4 Citations
15 Claims
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1. A voice band expander for expanding a frequency band of an input voice signal with a frequency spectrum limited to frequencies below an upper limit, the voice band expander comprising:
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a reduced signal generator for generating, from the input voice signal, a reduced signal with a modified frequency spectrum in which magnitudes of the frequencies in the entire frequency spectrum of the input voice signal are reduced; a band expanding signal generator for generating, from the reduced signal, a band expanding signal having a frequency spectrum in a band higher than the upper limit of the limited band of the input voice signal; and a band expanded signal generator for combining the input voice signal and the band expanding signal, thereby to form a band expanded signal with an expanded frequency band, wherein the reduced signal generator reduces the frequency spectral envelope and the harmonic structure of the input voice signal, the reduced signal generator comprising; a linear predictive coding (LPC) analyzer for carrying out an LPC analysis of the input voice signal; an LPC filter for reducing the frequency spectral envelope of the input voice signal by using LPC coefficients obtained by the LPC analyzer; a pitch analyzer, responsive to the output of the LPC filter, for determining a pitch and pitch intensity of the input voice signal; and a pitch filter for reducing the harmonic structure of the input voice signal according to the pitch and pitch intensity obtained by the pitch analyzer. - View Dependent Claims (2, 3)
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4. A voice band expander for expanding a frequency band of an input voice signal with a frequency spectrum limited to frequencies below an upper limit, the voice band expander comprising:
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a reduced signal generator for generating, from the input voice signal, a reduced signal with a modified frequency spectrum in which a harmonic structure of the input voice signal is reduced; a band expanding signal generator for generating, from the reduced signal, a band expanding signal having a frequency spectrum in a band higher than the upper limit of the limited band of the input voice signal; and a band expanded signal generator for combining the input voice signal and the band expanding signal, thereby to form a band expanded signal with an expanded frequency band, wherein the reduced signal generator reduces the harmonic structure of the input voice signal, the reduced signal generator further comprising; a pitch analyzer for determining a pitch and pitch intensity of the input voice signal; and a pitch filter for reducing the harmonic structure of the input voice signal according to the pitch and pitch intensity obtained by the pitch analyzer. - View Dependent Claims (5, 6, 7, 8)
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9. A method of expanding a frequency band of an input voice signal with a frequency spectrum limited to frequencies below an upper limit, the method comprising:
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generating, from the input voice signal, a reduced signal with a reduced frequency spectrum in which a harmonic structure of the input voice signal is reduced; generating, from the reduced signal, a band expanding signal having a frequency spectrum in a band higher than the upper limit of the limited band of the input voice signal; and combining the input voice signal and the band expanding signal and thereby forming a band expanded signal with an expanded frequency band, wherein generating the reduced signal comprises; determining a pitch and pitch intensity of the input voice signal; and reducing the harmonic structure of the input voice signal according to the pitch and pitch intensity. - View Dependent Claims (10, 11, 12, 14)
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13. A tangible machine-readable medium storing a voice band expansion program to be executed by a computer to expand a frequency band of an input voice signal with a frequency spectrum limited to frequencies below an upper limit, the voice band expansion program including:
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instructions for generating, from the input voice signal, a reduced signal with a reduced frequency spectrum in which a harmonic structure of the input voice signal is reduced; instructions for generating, from the reduced signal, a band expanding signal having a frequency spectrum in a band higher than the upper limit of the limited band of the input voice signal; and instructions for combining the input voice signal and the band expanding signal and thereby forming a band expanded signal with an expanded frequency band, wherein the instructions for generating the reduced signal includes; instructions for determining a pitch and pitch intensity of the input voice signal; and instructions for reducing the harmonic structure of the input voice signal according to the pitch and pitch intensity. - View Dependent Claims (15)
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Specification