用MATLAB播放了一段正弦信号，用音频线和5509a板子的mic口连接，采集的音频信号峰值均被削平，怎么解决呢?
采集代码如下：
i2c_status = I2C_write( analog_aduio_path_control_MIC,//pointer to data array
2, //length of data to be transmitted
1, //master or slaver
CODEC_ADDR, //slave address to transmit to
1, //transfer mode of operation
30000 //time out for bus busy
);
for(i=0;i<INPUTNUMBER;i++)
{
while(!MCBSP_xrdy(hMcbsp)){};
aic23data = MCBSP_read16(hMcbsp);
for(j=3000;j>0;j--);
while(!MCBSP_rrdy(hMcbsp)){};
firin[i+FIR_LEN]=aic23data;
其中firin为int型，aic23data为 unit 16
