Speech decoding method and apparatus for selecting random noise codevectors as excitation signals for an unvoiced speech frame
First Claim
1. A speech decoding method for decoding an encoded speech signal produced by dividing an input speech signal on a time axis using a pre-set encoding unit and by waveform-encoding a resulting encoding-unit-based time-axis waveform signal, said method comprising:
- a waveform-decoding step for producing an encoding-unit-based time-axis waveform signal, wherein said time-axis waveform signal is an excitation signal for synthesis of an unvoiced speech signal;
an error detecting step for detecting an error using an error checking code appended to said encoded speech signal; and
an evading step for evading repeated use of a same waveform as a waveform used in said waveform-decoding step by using a waveform different from a directly preceding waveform when an error is detected in said error detecting step.
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Abstract
If the same parameter is repeatedly used in an unvoiced frame inherently devoid of pitch, there is produced a pitch of the frame length period, thus producing an extraneous feeling. This can be prevented from occurring by evading repeated use of excitation vectors having the same waveform shape. To this end, when decoding an encoded speech signal obtained on waveform encoding an encoding-unit-based time-axis speech signal obtained on splitting an input speech signal in terms of a pre-set encoding unit on the time axis, input data is checked by CRC by a CRC and bad frame masking circuit 281, which processes a frame corrupted with an error with bad frame masking of repeatedly using parameters of a directly previous frame. If the error-corrupted frame is unvoiced, an unvoiced speech synthesis unit 220 adds the noise to an excitation vector from a noise codebook or randomly selects the excitation vector of the noise codebook.
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Citations
11 Claims
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1. A speech decoding method for decoding an encoded speech signal produced by dividing an input speech signal on a time axis using a pre-set encoding unit and by waveform-encoding a resulting encoding-unit-based time-axis waveform signal, said method comprising:
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a waveform-decoding step for producing an encoding-unit-based time-axis waveform signal, wherein said time-axis waveform signal is an excitation signal for synthesis of an unvoiced speech signal; an error detecting step for detecting an error using an error checking code appended to said encoded speech signal; and an evading step for evading repeated use of a same waveform as a waveform used in said waveform-decoding step by using a waveform different from a directly preceding waveform when an error is detected in said error detecting step. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A speech decoding apparatus for decoding an encoded speech signal produced by dividing an input speech signal on a time axis using a pre-set encoding unit and by waveform-encoding a resulting encoding-unit-based time-axis waveform signal, said apparatus comprising:
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waveform-decoding means for waveform-decoding said encoded speech signal and for producing an encoding-unit-based time-axis waveform signal, wherein said time-axis waveform signal is an excitation signal for synthesis of an unvoiced speech signal; error detection means for detecting an error using an error checking code appended to said encoded speech signal; and evading means for evading repeated use of a same waveform as a waveform used by said waveform-decoding means by using a waveform different from a directly-preceding waveform when an error is detected by said error detection means. - View Dependent Claims (8, 9, 10, 11)
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Specification