C语言实现LPC编码例程

以下是一个简单的C语言实现LPC编码的例程，包括预加重、窗口处理、LPC分析、LPC系数量化和编码等步骤：

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#define FRAME_SIZE 160   // 一帧语音信号的采样点数
#define ORDER 10         // LPC模型的阶数

int main()
{
    // 读入语音信号
    int speech[FRAME_SIZE];
    FILE *fp;
    if ((fp = fopen("speech.pcm", "rb")) == NULL)
    {
        printf("Can't open input file!\n");
        exit(1);
    }
    fread(speech, sizeof(short), FRAME_SIZE, fp);
    fclose(fp);
    
    // 预加重
    double preemph = 0.97;  // 预加重系数
    double pre_speech[FRAME_SIZE];
    for (int i = 0; i < FRAME_SIZE; i++)
    {
        if (i == 0)
            pre_speech[i] = speech[i];
        else
            pre_speech[i] = speech[i] - preemph * speech[i-1];
    }
    
    // 窗口处理
    double window[FRAME_SIZE];
    for (int i = 0; i < FRAME_SIZE; i++)
    {
        window[i] = 0.54 - 0.46 * cos(2 * M_PI * i / (FRAME_SIZE - 1));
        pre_speech[i] *= window[i];
    }
    
    // LPC分析
    double r[ORDER+1];
    for (int k = 0; k <= ORDER; k++)
    {
        double sum = 0.0;
        for (int n = 0; n < FRAME_SIZE-k; n++)
            sum += pre_speech[n] * pre_speech[n+k];
        r[k] = sum;
    }
    
    double a[ORDER+1];
    double e = r[0];
    for (int i = 1; i <= ORDER; i++)
    {
        double sum = 0.0;
        for (int j = 1; j < i; j++)
            sum += a[j] * r[i-j];
        a[i] = (r[i] - sum) / e;
        for (int j = 1; j < i; j++)
            a[j] = a[j] - a[i] * a[i-j];
        e *= (1.0 - a[i] * a[i]);
    }
    
    // LPC系数量化
    double max_abs = 0.0;
    for (int i = 1; i <= ORDER; i++)
        if (fabs(a[i]) > max_abs)
            max_abs = fabs(a[i]);
    int scale = (int)ceil(log(max_abs) / log(2.0)) - 1;
    double factor = pow(2.0, scale);
    int q_a[ORDER+1];
    for (int i = 1; i <= ORDER; i++)
        q_a[i] = (int)floor(a[i] / factor + 0.5);
    
    // 编码
    int code[ORDER+1];
    for (int i = 1; i <= ORDER; i++)
    {
        if (q_a[i] >= 0)
            code[i] = q_a[i] * 2;
        else
            code[i] = (-q_a[i] * 2 - 1);
    }
    
    // 输出编码结果
    printf("LPC coefficients:\n");
    for (int i = 1; i <= ORDER; i++)
        printf("%d ", q_a[i]);
    printf("\nCode:\n");
    for (int i = 1; i <= ORDER; i++)
        printf("%d ", code[i]);
    printf("\n");
    
    return 0;
}

注意，以上例程仅为演示LPC编码的基本过程，实际应用中还需要考虑很多细节问题，如语音信号的预处理、LPC分析算法的优化、LPC系数的量化方式、编码的压缩效果等。同时，解码也是一个重要的问题，需要注意解码误差的影响。