Higher Formants, f4, f5, b4, and b5

A male voice typically has five prominent resonant peaks in the spectrum (over the range from 0 to 5 kHz), a female voice typically has only four (because of a smaller head size), and a child has three. If fourth and fifth formant resonances exist for a particular voice, they are fixed in frequency and bandwidth characteristics. These characteristics are specified in Hz by the options f4, f5, b4, and b5.

If a higher formant does not exist, the frequency and bandwidth of the speaker definition are set to special values that cause the resonance to disappear. To make a resonance disappear, the frequency is set to above 5500 Hz and the bandwidth is set to 5500 Hz. (This disables the formant filter.) This is what has been done to the fourth and fifth formants for Kit.

The permitted values for the f4 and f5 options have fairly complicated restrictions. Violating these restrictions can cause overloads and squawks. The following restrictions apply to cases where a higher formant exists:

The f5 option must be at least 300 Hz higher than f4.

If sx is 1 (male), f4 must be at least 3250 Hz.

If sx is 0 (female), f4 must be at least 3700 Hz.

If hs is not 100, the preceding values should be multiplied by (hs / 100).

These higher formants produce peaks in the spectrum that become more prominent if the b4 and b5 options are smaller, and if the f4 and f5 options are closer together. The limits placed on the b4 and b5 options should ensure that no problems occur. However, smaller values for bandwidths may produce an overload in the synthesizer. You can correct these overloads by increasing the bandwidths or by changing the gain control, g1.