The random perturbations of pitch and amplitudeare always an integral part of quasi-periodic vocal musical waves. Perturbations in pitch and amplitude are one of the important measures of timbre in vocal music. These perturbations in pitch and amplitude areknown as jitter and shimmer, respectively. The results, inter alia, indicate that these are basically aerodynamic in nature, caused by the physical properties of the voice source, particularly the non-rigidity of vocal folds. Measures of such perturbations reveal the physical property, hence the timbre characteristics of the voice source. In this work, an attempt has been made to study the effect of vocal F0 on jitter and shimmer in the signals of four trained singers of both sexes and three non-singers, all are male subjects. Intracorrelations between the two parameters were studied. Highly trained singers are known to possess a fine skill of pitch control. It has been found that the values of jitter and shimmer are higher in the case of trained singers than in that of non-singers, and the interdependence between the parameters is significantly higher in the case of trained singers. This is due to larger control of singers on the vocal apparatuses by rigorous training. The values of jitter and shimmer and the corresponding standard deviation are very similar for different individuals in the same class. For non-singers, jitter and shimmer are lower than those of the singers. It seems that the significantly large values of jitter and shimmer for singers indirectly point towards the more relaxed vocal folds, presumably because of long periods of vocal training. We have observed no significant difference in these parameters between male and female subjects.