Sending Serial Hex Command from Pin 1 (Tx)
there are 6 bytes just make 

byte muteON[] = {0xAA,0x13,0xFE,0x01,0x01,0x13};
byte muteOFF[] = {0XAA,0x13,0xFE,0x01,0x00,0x12};
...
/* To send mute ON comand */
for(byte i =0;i&lt;sizeof(muteON);i++)(Serial.write(muteON[i]));
/* To send mute OFF comand */
for(byte i =0;i&lt;sizeof(muteOFF);i++)(Serial.write(muteOFF[i]));