Series 1 is real (from MIT-BIH Normal Sinus Rhythm Database record 16265); series 2 is synthesized using a slightly elaborated version of the example, in which generate looks like this:

float generate(void)
{
    float rr;
    static float t;
    static float omega = 1.0;
    static float rrmean = 0.8;

    omega += ((float)rand() - RAND_MAX)/(RAND_MAX*100.0) + 0.005;
    if (omega < 0.5) omega = 0.5 + ((float)rand())/(RAND_MAX*100.0);
    else if (omega > 2.0) omega = 2.0 - ((float)rand())/(RAND_MAX*100.0);
    rrmean += ((float)rand() - RAND_MAX)/(RAND_MAX*100.0) + 0.005;
    if (rrmean < 0.6) rrmean = 0.6 + ((float)rand())/(RAND_MAX*100.0);
    else if (rrmean > 1.1) rrmean = 1.1 - ((float)rand())/(RAND_MAX*100.0);
    rr = rrmean + 0.05*sin(omega*t) +
	((float)rand() - RAND_MAX)/(RAND_MAX*100.0);
    t += rr;
    return (rr);
}