Speech coding and decoding apparatus
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FIG. 4 is a block diagram showing a coding apparatus according to the first embodiment. A speech signal s(n) after A / D conversion is input to a frame buffer 102, which accumulates the speech signal s(n) for one frame. Individual elements in FIG. 4 perform the following processes frame by frame.
A prediction parameter calculator 108 receives the speech signal s(n) from the frame buffer 102, and computes a predetermined number, p, of prediction parameters (LPC parameter or reflection coefficient) by an autocorrelation method or covariance method. The acquired prediction parameters are sent to a prediction parameter coder 110, which codes the prediction parameters based on a predetermined number of quantization bits, and outputs the codes to a decoder 112 and a multiplexer 118. The decoder 112 decodes the received codes of the prediction parameters and sends decoded values to a prediction filter 106 and an excitation signal generator 104. The prediction filter 106 receives the speech si...
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Now the second embodiment will be explained. Although the excitation pulse is computed by the A-b-S (Analysis by Synthesis) method in the first embodiment, the excitation pulse may be analytically calculated as another method.
Here, first, let N (samples) be the frame length, M be the number of subframes, L (samples) be the subframe length, N.sub.m (1.ltoreq.m.ltoreq.M) be the interval of the excitation pulse in the m-th subframe, Q.sub.m be the number of excitation pulses, g.sub.i.sup.(m) (1.ltoreq.i.ltoreq.Q.sub.m) be the amplitude of the excitation pulse, and K.sub.m be the phase of the excitation pulse. Here there is the following relation.
where .left brkt-bot..multidot..right brkt-bot. indicates computation to provide an integer portion by rounding off.
FIG. 7 illustrates an example of the excitation signal in a case where M=5, L=8, N.sub.1 =N.sub.3 =1, N.sub.2 =N.sub.4 =N.sub.5 =2, Q.sub.1 =Q.sub.3 =8, Q.sub.2 =Q.sub.4 =Q.sub.5 =4, and K.sub.1 =K.sub.2 =K.sub.3 =K.sub.4 =1. Let ...
Example
FIG. 9 is a block diagram showing a coding apparatus according to the third embodiment, and FIG. 11 is a block diagram of a decoding apparatus according to the third embodiment. In FIG. 9, a speech signal after A / D conversion is input to a frame buffer 202, which accumulates the speech signal for one frame. Therefore, individual elements in FIG. 9 perform the following processes frame by frame.
A prediction parameter calculator 204 calculates prediction parameters using a known method. When a prediction filter 206 is constituted to have a long-term prediction filter (pitch prediction filter) 240 and a short-term prediction filter 242 cascade-connected as shown in FIG. 10, he prediction parameter calculator 204 calculates a pitch period, a pitch prediction coefficient, and a linear prediction coefficient (LPC parameter or reflection coefficient) by a know method, such as an autocorrelation method or covariance method. The calculation method is described in the document 2.
The calculate...
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