float fs = 500.0; // sampling frq - 2ms sampling interval 
int sig_A1[100]; // to store signal  
int sig_A2[100];
int sig_B1[100];
int sig_B2[100];
float t;

void setup() {
int f_A1 = 2 ; // signal frequency
int f_A2 = 3;
int f_B1 = 4;
int f_B2 = 5;

  pinMode(13,OUTPUT);
  // generate sin signal
  for(int i=0;i<500;i++)
  {
    t = (float)i/fs;
    sig_A1[i] = int(127.0*(sin(2*PI*f_A1*t)+1.0)); // sign vale shift 0-2 
  }
   pinMode(12,OUTPUT);
  // generate sin signal
  for(int i=0;i<500;i++)
  {
    t = (float)i/fs;
    sig_A2[i] = int(127.0*(sin(2*PI*f_A2*t)+1.0)); // sign vale shift 0-2 
  }
     pinMode(11,OUTPUT);
  // generate sin signal
  for(int i=0;i<500;i++)
  {
    t = (float)i/fs;
    sig_B1[i] = int(127.0*(sin(2*PI*f_B1*t)+1.0)); // sign vale shift 0-2 
  }
      pinMode(10,OUTPUT);
  // generate sin signal
  for(int i=0;i<500;i++)
  {
    t = (float)i/fs;
    sig_B2[i] = int(127.0*(sin(2*PI*f_B2*t)+1.0)); // sign vale shift 0-2 
  }
}

void loop() {

for (int i = 0; i <500; i++)
{
  analogWrite(13,sig_A1[i]); 
  delay(2);
  analogWrite(12,sig_A2[i]);
  delay(2); // sampling interval 
  analogWrite(11,sig_B1[i]);
  delay(2);
  analogWrite(10,sig_B2[i]);
  delay(2); // sampling interval
}
}