Highlights • Speech activity factor is one of the important reference signal characteristics, especially when comes to time-varying impairments, like packet loss, etc. • This parameter is defined very broadly by the ITU-T Recommendation P.862.3. • The impact of this parameter on speech quality is thoroughly investigated from subjective and objective perspective (quality predictions provided by PESQ) in this study/paper. • Higher values of the parameter result in higher PESQ sensitivity to loss change as well as PESQ’s predictions accuracy improvement. • Human brain is a bit less sensitive to loss of some parts of words than PESQ.