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sin.cos表必须放大成整数.
我的一段代码:
// cos, sin表. 比特倒序表. 共128个点: == sin(2*PI*n/N); cos(2*PI*n/N). 放大128倍
flash char sin_tab[SAMPLE_NUM] = { 0, 6, 12, 18, 24, 30, 36, 42, 48, 54, 59, 65, 70, 75, 80, 85, 89, 94, 98, 102, 105, 108, 112, 114, 117, 119, 121, 123, 124, 125, 126, 126, 126, 126, 126, 125, 124, 123, 121, 119, 117, 114, 112, 108, 105, 102, 98, 94, 89, 85, 80, 75, 70, 65, 59, 54, 48, 42, 36, 30, 24, 18, 12, 6, 0, -6, -12, -18, -24, -30, -36, -42, -48, -54, -59, -65, -70, -75, -80, -85, -89, -94, -98, -102, -105, -108, -112, -114, -117, -119, -121, -123, -124, -125, -126, -126, -126, -126, -126, -125, -124, -123, -121, -119, -117, -114, -112, -108, -105, -102, -98, -94, -89, -85, -80, -75, -70, -65, -59, -54, -48, -42, -36, -30, -24, -18, -12, -6 };
flash char cos_tab[SAMPLE_NUM] = { 127, 126, 126, 125, 124, 123, 121, 119, 117, 114, 112, 108, 105, 102, 98, 94, 89, 85, 80, 75, 70, 65, 59, 54, 48, 42, 36, 30, 24, 18, 12, 6, 0, -6, -12, -18, -24, -30, -36, -42, -48, -54, -59, -65, -70, -75, -80, -85, -89, -94, -98, -102, -105, -108, -112, -114, -117, -119, -121, -123, -124, -125, -126, -126, -126, -126, -126, -125, -124, -123, -121, -119, -117, -114, -112, -108, -105, -102, -98, -94, -89, -85, -80, -75, -70, -65, -59, -54, -48, -42, -36, -30, -24, -18, -12, -6, 0, 6, 12, 18, 24, 30, 36, 42, 48, 54, 59, 65, 70, 75, 80, 85, 89, 94, 98, 102, 105, 108, 112, 114, 117, 119, 121, 123, 124, 125, 126, 126 };
flash char inv_tab[SAMPLE_NUM] = { 0, 64, 32, 96, 16, 80, 48, 112, 8, 72, 40, 104, 24, 88, 56, 120, 4, 68, 36, 100, 20, 84, 52, 116, 12, 76, 44, 108, 28, 92, 60, 124, 2, 66, 34, 98, 18, 82, 50, 114, 10, 74, 42, 106, 26, 90, 58, 122, 6, 70, 38, 102, 22, 86, 54, 118, 14, 78, 46, 110, 30, 94, 62, 126, 1, 65, 33, 97, 17, 81, 49, 113, 9, 73, 41, 105, 25, 89, 57, 121, 5, 69, 37, 101, 21, 85, 53, 117, 13, 77, 45, 109, 29, 93, 61, 125, 3, 67, 35, 99, 19, 83, 51, 115, 11, 75, 43, 107, 27, 91, 59, 123, 7, 71, 39, 103, 23, 87, 55, 119, 15, 79, 47, 111, 31, 95, 63, 127 };
// 128个整数实部,虚部的累加和
short FftReal[SAMPLE_NUM]; // fft的实部
short FftImage[SAMPLE_NUM]; // fft的虚部
LIGHT_SOUND LightSound; // 发送给计算机的频谱( 单字节频谱 )
UCHAR power; // 平均值
// fft运算时的变量.寄存器/全局变量可以加快运算速度
register UCHAR i,j,k,b,p; // 用寄存器变量,加快速度
register short TR,TI,temp; // 中间变量
ULONG ulReal; // 平方/开方
ULONG ulImage;
// 初始化
void InitFft()
{
SampAdd = sqrt_16(SampAdd/SAMPLE_NUM); // 功率值
power = SampAdd; // 功率值
for( i=0; i<SAMPLE_NUM; i++ )
{
FftReal[i] = SampleValue[i]; // SampleValue里时10位的AD结果
FftImage[i] = 0;
}
}
/* 128点的FFT运算. 采样数据已经按'比特倒序'放置在FftReal[]里
输出的结果也放在: FftRead[]里
*/
void FFT( )
{
/************** following code FFT *******************/
for( i=1; i<=NUM_2_LOG; i++) /* for(1) */
{
b=1;
b <<= (i-1); /*b= 2^(L-1) */
for( j=0; j<=b-1; j++) /* for (2) */
{
p=1;
p <<= (NUM_2_LOG-i);
p = p*j;
for( k=j; k<SAMPLE_NUM; k=k+2*b) /* for (3) 2点的dft */
{
TR = FftReal[k]; TI = FftImage[k]; temp = FftReal[k+b];
FftReal[k] = FftReal[k] + ((FftReal[k+b]*cos_tab[p])>>7) + ((FftImage[k+b]*sin_tab[p])>>7);
FftImage[k] = FftImage[k] - ((FftReal[k+b]*sin_tab[p])>>7) + ((FftImage[k+b]*cos_tab[p])>>7);
FftReal[k+b] = TR - ((FftReal[k+b]*cos_tab[p])>>7) - ((FftImage[k+b]*sin_tab[p])>>7);
FftImage[k+b] = TI + ((temp*sin_tab[p])>>7) - ((FftImage[k+b]*cos_tab[p])>>7);
// 移位.防止溢出. 结果已经是本值的 1/64
FftReal[k] >>= 1;
FftImage[k] >>= 1;
FftReal[k+b] >>= 1;
FftImage[k+b] >>= 1;
} /* END for (3) */
} /* END for (2) */
} /* END for (1) */
// 计算复数的模. 结果保存到虚部里, 发送给计算机.同时进行下次的采样,采样数据放入实部里
// FftImage[i] = sqrt( 1.0*FftReal[i]*FftReal[i] + 1.0*FftImage[i]*FftImage[i] );
SoundFrenMax = 0; // 保存频谱的最大值
for( i=0; i<SAMPLE_NUM/2; i++)
{
ulReal = FftReal[i];
ulReal *= ulReal;
ulImage = FftImage[i];
ulImage *= ulImage;
LightSound.value[i] = sqrt_16( ulReal + ulImage );
if( i == 0 )
LightSound.value[i] /= 4; // 直流分量的特别处理
if( LightSound.value[i] < FFT_OUT_MIN ) // 太小的值人为是0
LightSound.value[i] = 0;
if( LightSound.value[i] > SoundFrenMax ) // 保存最大值
SoundFrenMax = LightSound.value[i];
}
}
/****************************************/
/*Function: 开根号处理 */
/*入口参数：被开方数，长整型 */
/*出口参数：开方结果，整型 */
/****************************************/
short sqrt_16( ULONG M) // 快速long型开方
{
unsigned int N, i;
unsigned long tmp, ttp; // 结果、循环计数
if( M == 0 ) // 被开方数，开方结果也为0
return 0;
N = 0;
tmp = ( M >> 30 ); // 获取最高位：B[m-1]
M <<= 2;
if( tmp > 1 ) // 最高位为1
{
N ++; // 结果当前位为1，否则为默认的0
tmp -= N;
}
for( i=15; i>0; i-- ) // 求剩余的15位
{
N <<= 1; // 左移一位
tmp <<= 2;
tmp += (M >> 30); // 假设
ttp = N;
ttp = (ttp<<1)+1;
M <<= 2;
if( tmp >= ttp ) // 假设成立
{
tmp -= ttp;
N ++;
}
}
return N;
}
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