Nopen Fixed, nf

The number of samples in the open part of the glottal cycle is determined not only by the ri option, but also by a second option, nf. The Nopen Fixed (nf) option is the number of fixed samples in the open portion of the glottal cycle.

Most speakers adjust the open phase to be a certain fraction of the period, and this fraction is determined by the ri option. Other speakers keep the open phase fixed in duration when the overall period varies. To simulate this behavior, set the ri option to 100 and adjust the nf option to the desired duration of the open phase. The shortest possible open phase is 10 (1 ms), and the longest is three quarters of the period duration (about 70 for a male voice).