Speech decoder capable of reproducing well background noise
First Claim
1. A speech decoder comprising:
- decoding means for decoding a binary coded input signal into a spectral parameter, an average amplitude, a pitch period and a sound source signal;
speech detecting means for detecting a non-speech interval and a speech interval using at least one among the spectral parameter, the average amplitude and the pitch period;
excitation signal generating means for generating an excitation signal using the sound source signal, the average amplitude, and the pitch period;
first signal reproducing means for reproducing a sound signal using the excitation signal from the excitation signal generating means and the spectral parameter from said decoding means;
memorizing means for memorizing a random number code book storing random number code vectors which can be used in reproducing sound signals;
searching means for searching the random number code book and selecting a random number code vector which can be used to reproduce a sound signal that is closest to the output signal reproduced in the non-speech interval by said first signal reproducing means;
second signal reproducing means for reproducing a sound signal using the spectral parameter from said decoding means and the random number code vector which has been searched by said searching means; and
switching means for outputting the sound signal from said first signal reproducing means in the speech interval and outputting the sound signal from said second signal reproducing means in the non-speech interval.
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Abstract
When background noise is superposed on speech, a speech decoder can well represent the background noise through signal processing only in the speech decoder even at low bit rates. In the speech decoder, a decoding circuit receives a signal from a speech coder, a speech detecting circuit detects non-speech and speech intervals, and a excitation signal calculating circuit calculates a excitation signal using a sound source signal, a pitch period, and an average amplitude. A signal reproducing circuit drives a filter composed of a spectrum parameter to reproduce a sound signal. A searching circuit stores a set of random number code vectors of a predetermined bit number as a code book, and searches the code book for a best random number code vector which is selected. A second signal reproducing circuit reproduces a sound signal (noise) using the selected random number code vector.
47 Citations
10 Claims
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1. A speech decoder comprising:
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decoding means for decoding a binary coded input signal into a spectral parameter, an average amplitude, a pitch period and a sound source signal; speech detecting means for detecting a non-speech interval and a speech interval using at least one among the spectral parameter, the average amplitude and the pitch period; excitation signal generating means for generating an excitation signal using the sound source signal, the average amplitude, and the pitch period; first signal reproducing means for reproducing a sound signal using the excitation signal from the excitation signal generating means and the spectral parameter from said decoding means; memorizing means for memorizing a random number code book storing random number code vectors which can be used in reproducing sound signals; searching means for searching the random number code book and selecting a random number code vector which can be used to reproduce a sound signal that is closest to the output signal reproduced in the non-speech interval by said first signal reproducing means; second signal reproducing means for reproducing a sound signal using the spectral parameter from said decoding means and the random number code vector which has been searched by said searching means; and switching means for outputting the sound signal from said first signal reproducing means in the speech interval and outputting the sound signal from said second signal reproducing means in the non-speech interval. - View Dependent Claims (2, 3, 4, 5)
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6. A speech decoder comprising:
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decoding means for decoding a binary coded input signal into a spectral parameter, an average amplitude, a pitch period and a sound source signal; speech detecting means for detecting a non-speech interval and a speech interval using at least one among the spectral parameter, the average amplitude and the pitch period; excitation signal generating means for generating a excitation signal using the sound source signal, the average amplitude, and the pitch period; memorizing means for memorizing a random number code book storing random number code vectors which can be used in reproducing sound signals; searching means for searching the random number code book for a random number code vector which can be used in reproducing a sound signal that is closest to the excitation signal in the non-speech interval; switching means for outputting the excitation signal from said excitation signal generating means in the speech interval and outputting the random number code vector which has been searched in the non-speech interval by said searching means; and signal reproducing means for reproducing a sound signal using the spectral parameter from said decoding means and the output from the switching means. - View Dependent Claims (7, 8, 9, 10)
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Specification