Communication system capable of improving a speech quality by classifying speech signals
First Claim
1. In an encoder device supplied with a sequence of digital speech signals to produce a sequence of output signals, the sequence of said digital speech signals forming a frame, said encoder device comprising parameter calculation means responsive to said sequence of the digital speech signals for calculating first and second primary parameters which specify a spectrum envelope and a pitch of said sequence of the digital speech signals to produce first and second parameter signals representative of said spectrum envelope and said pitch, respectively, primary calculation means coupled to said parameter calculation means for calculating a set of calculation result signals representative of the sequence of said digital speech signals, and output signal producing means for successively rendering said set of the calculation result signals into the sequence of said output signals, the improvement wherein said encoder device comprises:
- subsidiary parameter extracting means supplied with the sequence of said digital speech signals and said first and said second primary parameter signals for extracting, from the sequence of said digital speech signals, a subsidiary parameter which is different from said first and said second primary parameters and which specifies a selected one of at least three species of said sequence of the digital speech signals to classify the sequence of said digital speech signals into one of said at least three classes corresponding to said at least three species, respectively, and to produce a class identification signal representative of each of said sequence of said digital speech signals to produce a class identification signal representative of each of said at least three classes;
means for producing said class identification signal as a monitoring result signal representative of a result of monitoring said subsidiary parameter;
processing means supplied with said digital speech signals, said first and second primary parameter signals, and said monitoring result signal for processing said digital speech signals to selectively produce a first set of primary sound source signals and a second set of secondary sound source signals different from said first set of the primary sound source signals, said first set of the primary sound source signals being formed by a set of excitation pulses calculated with respect to a selected one of subframes which result from dividing every frame in dependency upon said second primary parameter signal and each of which is shorter than said frame andmeans for supplying a combination of said primary and said secondary sound source signals to said output signal producing means as said calculation result signals.
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Abstract
A communication system having an encoder device used in combination with a decoder device for encoding a sequence of digital speech signals into a sequence of output signals, using a spectrum parameter and a pitch parameter. A subsidiary parameter of the digital speech signals is detected and monitored by a monitoring circuit. Digital speech signals are classified into voiced sound or voiceless sound and into vocality, nasal, fricative, or explosive durations at every frame. When a voiced sound, i.e., a vocality is detected, a predetermined number of excitation pulses are calculated during a representative subframe and are produced as primary sound source signals. A subsidiary information signal is produced during the remaining subframes to represent phase and amplitude correction factors in each of the subframes. When a voiceless sound, i.e., the nasal, the fricative, or the explosive is detected, noise signals and/or a plurality of excitation pulses are calculated for each frame and produced as secondary sound source signals.
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Citations
7 Claims
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1. In an encoder device supplied with a sequence of digital speech signals to produce a sequence of output signals, the sequence of said digital speech signals forming a frame, said encoder device comprising parameter calculation means responsive to said sequence of the digital speech signals for calculating first and second primary parameters which specify a spectrum envelope and a pitch of said sequence of the digital speech signals to produce first and second parameter signals representative of said spectrum envelope and said pitch, respectively, primary calculation means coupled to said parameter calculation means for calculating a set of calculation result signals representative of the sequence of said digital speech signals, and output signal producing means for successively rendering said set of the calculation result signals into the sequence of said output signals, the improvement wherein said encoder device comprises:
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subsidiary parameter extracting means supplied with the sequence of said digital speech signals and said first and said second primary parameter signals for extracting, from the sequence of said digital speech signals, a subsidiary parameter which is different from said first and said second primary parameters and which specifies a selected one of at least three species of said sequence of the digital speech signals to classify the sequence of said digital speech signals into one of said at least three classes corresponding to said at least three species, respectively, and to produce a class identification signal representative of each of said sequence of said digital speech signals to produce a class identification signal representative of each of said at least three classes; means for producing said class identification signal as a monitoring result signal representative of a result of monitoring said subsidiary parameter; processing means supplied with said digital speech signals, said first and second primary parameter signals, and said monitoring result signal for processing said digital speech signals to selectively produce a first set of primary sound source signals and a second set of secondary sound source signals different from said first set of the primary sound source signals, said first set of the primary sound source signals being formed by a set of excitation pulses calculated with respect to a selected one of subframes which result from dividing every frame in dependency upon said second primary parameter signal and each of which is shorter than said frame and means for supplying a combination of said primary and said secondary sound source signals to said output signal producing means as said calculation result signals. - View Dependent Claims (2, 3, 4, 5)
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6. In an encoder device supplied with a sequence of digital speech signals to produce a sequence of output signals, the sequence of said digital speech signals forming a frame, said encoder device comprising parameter calculation means responsive to said sequence of the digital speech signals for calculating first and second primary parameters which specify a spectrum envelope and a pitch of said sequence of the digital speech signals to produce first and second parameter signals representative of said spectrum envelope and said pitch, respectively, primary calculation means coupled to said parameter calculation means for calculating a set of calculation result signals representative of the sequence of said digital speech signals, and output signal producing means for successively rendering said set of the calculation result signals into said output signals, said digital speech signals being classified as a voiced sound and a voiceless sound, the improvement wherein said primary calculation means comprises:
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processing means supplied with said digital speech signals and said first and said second primary parameters for processing said digital speech signals to selectively produce a first set of primary sound source signals and a second set of secondary sound source signals during said voiced sound and said voiceless sound, respectively, said first set of the primary sound source signals being formed by a set of excitation pulses calculated with respect to a selected one of subframes which result from dividing every frame in dependency upon said second primary parameter signal and each of which is shorter than said frame; and means for applying a combination of said first and said second sets of the sound source signals to said output signal producing means as said calculation result signals. - View Dependent Claims (7)
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Specification