Soft onset vocalization is used in certain speech therapies. However, it is not easy to practice it at home because the acoustical evaluation itself needs training. It would be helpful for speech patients to get objective feedback during training. In this paper, new parameters for identifying soft onset with high accuracy are described. One of the parameters measures an aspect of the soft voice onset, in which the vocal folds start to oscillate periodically before coming in contact with each other at the beginning of vocalization. Combined with an onset time exceeding a threshold, the proposed parameters gave about 99% accuracy in identifying soft onset vocalization.