The Average pitch (ap) option (average pitch, in Hz) and the Pitch range (pr) option (pitch ranges in % of normal range) options modify the computed values of fundamental frequency, f0, according to the formula:
f0' = ap + (((f0 - 120) * pr) / 100)
If the ap option is set to 120 Hz and the pr option to 100%, no change to the normal f0 contour is computed for a typical male voice. The effect of a change in the ap option is simply to raise or lower the entire pitch contour independently by a constant number of Hz, whereas the effect of the pr option is to expand or contract the swings in pitch about 120 Hz.
Normally, a smaller larynx simultaneously produces f0 values that are higher in average pitch and higher in pitch range by about the same factor (the whole f0 contour is multiplied by a constant factor). Observing the values assigned to the ap and pr options for each of the voices, you can see that the voices rank in average pitch from low (Harry) to high (Kit).
Rankings for the pr option are similar, except that Frank has a flat, nonexpressive pitch range as compared with his average pitch.
The best way to determine a good pitch range for a new voice is by trial and error. You can create a monotone or robotlike voice by setting the pitch range to 0. For example, to make Harry speak in a monotone at exactly 90 Hz, type the following command.
[:nh][:dv ap 90 pr 0] I am a robot.
Reducing the pitch range reduces the dynamics of the voice, producing emotions such as sadness in the speaker. Increasing the pitch range while leaving the average pitch the same or setting it slightly higher suggests excitement.
Due to constraints involved in pitch-synchronous updating of other dynamically changing options, the fundamental frequency contour that is computed by the preceding formula is then checked for values that are outside the following limits.
f0 maximum = 500 Hz
f0 minimum = 50 Hz
Any value outside this range is limited to fall within the range.
To keep you from exceeding reasonable limits on the options that control pitch, certain constraints apply to the values selected. If the Design Voice command specifies values outside these limits, the value is limited to the nearest listed value before execution.