Speech signal decoding method and apparatus
In a speech signal decoding method, information containing at least a sound source signal, gain, and filter coefficients is decoded from a received bit stream. Voiced speech and unvoiced speech of a speech signal are identified using the decoded information. Smoothing processing based on the decoded information is performed for at least either one of the decoded gain and decoded filter coefficients in the unvoiced speech. The speech signal is decoded by driving a filter having the decoded filter coefficients by an excitation signal obtained by multiplying the decoded sound source signal by the decoded gain using the result of the smoothing processing. A speech signal decoding apparatus is also disclosed.
1. A speech signal decoding apparatus comprising:
a plurality of decoding means for decoding information containing at least a sound source signal, a gain, and filter coefficients from a received bit stream;
smoothing means for obtaining a modified decoded information by modifying the decoded information of a current frame using the modified decoded information obtained at a previous frame to perform smoothing processing for at least either one of the decoded gain and the decoded filter coefficients contained in the decoded information;
means for obtaining an excitation signal by multiplying the decoded sound source signal by the decoded gain after performing the smoothing processing; and
means for decoding the speech signal by driving a filter having the decoded filter coefficients by the excitation signal obtained from the means for obtaining.
2. The apparatus as recited in claim 1 , wherein said decoding means decodes information containing pitch periodicity and a power of the speech signal from the received bit stream.
3. The apparatus as recited in claim 1 , further comprising:
identification means for identifying voiced speech and unvoiced speech of a speech signal using the decoded information, at least the unvoiced speech containing a background noise.
4. The apparatus as recited in claim 3 , wherein said identification means performs identification operation using a value obtained by averaging for a long term a variation amount based on a difference between the decoded filter coefficients and their long-term average.
5. A speech signal decoding apparatus comprising:
a plurality of decoding units configured to decode information containing at least a sound source signal, a gain, and filter coefficients from a received bit stream;
a smoothing unit configured to smooth a modified decoded information by modifying the decoded information of a current frame using the modified decoded information obtained at a previous frame to perform smoothing processing for at least either one of the decoded gain and the decoded filter coefficients contained in the decoded information;
an obtaining unit configured to obtain an excitation signal by multiplying the decoded sound source signal by the decoded gain after performing the smoothing processing; and
a decoding unit configured to decode the speech signal by driving a filter having the decoded filter coefficients by the excitation signal obtained from the obtaining unit.
6. The apparatus as recited in claim 5 , wherein said decoding unit decodes information containing pitch periodicity and a power of the speech signal from the received bit stream.
7. The apparatus as recited in claim 5 , further comprising:
an identification unit configured to identify identifying voiced speech and unvoiced speech of a speech signal using the decoded information, at least the unvoiced speech containing a background noise.
8. The apparatus as recited in claim 7 , wherein said identification unit performs identification operation using a value obtained by averaging for a long term a variation amount based on a difference between the decoded filter coefficients and their long-term average.
9. A speech signal method comprising:
decoding information containing at least a sound source signal, a gain, and filter coefficients from a received bit stream;
obtaining a modified decoded information by modifying the decoded information of a current frame using the modified decoded information obtained at a previous frame and performing smoothing processing for at least either one of the decoded gain and the decoded filter coefficients contained in the decoded information;
obtaining an excitation signal by multiplying the decoded sound source signal by the decoded gain after performing the smoothing processing; and
decoding the speech signal by driving a filter having the decoded filter coefficients by the excitation signal obtained from the obtaining step.
10. The method as recited in claim 9 , wherein said decoding step comprises:
decoding information containing pitch periodicity and a power of the speech signal from the received bit stream.
11. The method as recited in claim 9 , further comprising:
identifying voiced speech and unvoiced speech of a speech signal using the decoded information, at least the unvoiced speech containing a background noise.
12. The method as recited in claim 11 , wherein said identification step comprises:
performing an identification operation using a value obtained by averaging for a long term a variation amount based on a difference between the decoded filter coefficients and their long-term average.