Many frequencies generated at glottis

[Ross C]

How do the glottal pulses generate a wide range of frequencies rather than just the F0 of the open-close cycle at the glottis? Is this just because the flesh around it adds some random motion into the signal?

[Simon]

A simplified description of the vocal folds is that they are closed most of the time. The air pressure from the lungs eventually forces them to burst open and release the pressure, after which they snap shut very rapidly.

This is not random motion, but a very particular pattern of opening and closing.

The signal generated by one cycle of the vocal folds (mainly related to the very rapid closing) can be approximated as an impulse.

Hence, the acoustic wave generated at the glottis is approximately an impulse train. So, we use an impulse train as a model of this signal, and our model has just one parameter: F0.

In the literature on phonation you will of course find much more sophisticated descriptions and models than this. The glottal wave is not exactly an impulse train, but has a particular shape which can be parameterised – e.g., the Liljencrantz-Fant (LF) model has 4 parameters. This is beyond the scope of Speech Processing.

[Author]

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