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用16BIT 单片机AD 各DA，的ADPCM的编码与解码做录音方案，出来的音质还过得去！！算法如下：
/* Includes ------------------------------------------------------------------*/
#include "adpcm.h"
/* Private define ------------------------------------------------------------*/
/* Quantizer step size lookup table */
const uint16_t StepSizeTable[89]={7,8,9,10,11,12,13,14,16,17,
19,21,23,25,28,31,34,37,41,45,
50,55,60,66,73,80,88,97,107,118,
130,143,157,173,190,209,230,253,279,307,
337,371,408,449,494,544,598,658,724,796,
876,963,1060,1166,1282,1411,1552,1707,1878,2066,
2272,2499,2749,3024,3327,3660,4026,4428,4871,5358,
5894,6484,7132,7845,8630,9493,10442,11487,12635,13899,
15289,16818,18500,20350,22385,24623,27086,29794,32767};
/* Table of index changes */
const int8_t IndexTable[16]={0xff,0xff,0xff,0xff,2,4,6,8,0xff,0xff,0xff,0xff,2,4,6,8};
/* Private macro -------------------------------------------------------------*/
/* Private variables ---------------------------------------------------------*/
/* Private function prototypes -----------------------------------------------*/
/* Private functions ---------------------------------------------------------*/
/**
* @brief ADPCM_Encode.
* @param sample: a 16-bit PCM sample
* @retval : a 4-bit ADPCM sample
*/
uint8_t ADPCM_Encode(int32_t sample)
{
static int16_t index = 0;
static int32_t predsample = 0;
uint8_t code=0;
uint16_t tmpstep=0;
int32_t diff=0;
int32_t diffq=0;
uint16_t step=0;
step = StepSizeTable[index];
/* 2. compute diff and record sign and absolut value */
diff = sample-predsample;
if (diff < 0)
{
code=8;
diff = -diff;
}
/* 3. quantize the diff into ADPCM code */
/* 4. inverse quantize the code into a predicted diff */
tmpstep = step;
diffq = (step >> 3);
if (diff >= tmpstep)
{
code |= 0x04;
diff -= tmpstep;
diffq += step;
}
tmpstep = tmpstep >> 1;
if (diff >= tmpstep)
{
code |= 0x02;
diff -= tmpstep;
diffq+=(step >> 1);
}
tmpstep = tmpstep >> 1;
if (diff >= tmpstep)
{
code |=0x01;
diffq+=(step >> 2);
}
/* 5. fixed predictor to get new predicted sample*/
if (code & 8)
{
predsample -= diffq;
}
else
{
predsample += diffq;
}
/* check for overflow*/
if (predsample > 32767)
{
predsample = 32767;
}
else if (predsample < -32768)
{
predsample = -32768;
}
/* 6. find new stepsize index */
index += IndexTable[code];
/* check for overflow*/
if (index <0)
{
index = 0;
}
else if (index > 88)
{
index = 88;
}
/* 8. return new ADPCM code*/
return (code & 0x0f);
}
/**
* @brief ADPCM_Decode.
* @param code: a byte containing a 4-bit ADPCM sample.
* @retval : 16-bit ADPCM sample
*/
int16_t ADPCM_Decode(uint8_t code)
{
static int16_t index = 0;
static int32_t predsample = 0;
uint16_t step=0;
int32_t diffq=0;
step = StepSizeTable[index];
/* 2. inverse code into diff */
diffq = step>> 3;
if (code&4)
{
diffq += step;
}
if (code&2)
{
diffq += step>>1;
}
if (code&1)
{
diffq += step>>2;
}
/* 3. add diff to predicted sample*/
if (code&8)
{
predsample -= diffq;
}
else
{
predsample += diffq;
}
/* check for overflow*/
if (predsample > 32767)
{
predsample = 32767;
}
else if (predsample < -32768)
{
predsample = -32768;
}
/* 4. find new quantizer step size */
index += IndexTable [code];
/* check for overflow*/
if (index < 0)
{
index = 0;
}
if (index > 88)
{
index = 88;
}
/* 5. save predict sample and index for next iteration */
/* done! static variables */
/* 6. return new speech sample*/
return ((int16_t)predsample);
}
//////＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝
但后来项目用10BIT单片机 的AD与DA做，我采用移位把10BIT移成16BIT做编码，然后解码后16BIT移成10BIT,同上面算法，出来声音噪声很大！
不知怎么改想把上面的算法改成10BIT的编码与解码的算法！！
有没有做过类似东西的大哥哥出来支招啊！ |
阿莫论坛20周年了！感谢大家的支持与爱护！！
一只鸟敢站在脆弱的枝条上歇脚，它依仗的不是枝条不会断，而是自己有翅膀，会飞。
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发表于 2014-2-24 16:01:28
楼主
