LPC: To Formant

You can choose this command after selecting 1 or more LPC objects.


For each LPC frame, the zeros of the linear prediction polynomial are extracted. Zeros that are outside the unit circle are reflected into it. Next, formant frequencies and bandwidths are calculated from all the roots that have the imaginary part positive, i.e., that lie in the upper half of the unit circle. Formant frequencies smaller than 50 Hz or larger than (nyquistFrequency - 50) are discarded. The remaining frequencies and bandwidths are sorted and copied to the Formant frame. Finally, the gain field of the LPC is copied to the intensity field of the Formant frame.


The root finder is Laguerre's method followed by root polishing, see Press et al. (1992).


• The formant values can be very inaccurate if you did not resample the Sound before the LPC-analysis (consult the Source-filter synthesis tutorial).
• The results of the root finder may not always be accurate when more than 30 roots have to be found.

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