This method computes the formant frequency (candidate) tracks of a speech signal. The algorithm first detects the local peaks of the smoothed signal spectra (cepstrum or lpc) and then (optionally) applies a tracking algorithm to the peak array. The result is a set of parameter functions
FOF(t,i) (with: i = formant candidate index, from 0 to n-1) which can be saved in the DataSet.
- Defines the formant frequency search (fmin/fmax) and display range in Hz.
- Defines the threshold amplitudes (amin/amax) for peak detection in dB. The line between the points (fmin,amin) and (fmax,amax) is used as the threshold function .
- rel. to spg-maximum
- The amplitude values are calculated relative to the spectrogram's maximum amplitude.
- number of formants
- The maximum number of formant tracks to be computed. Note, that this does not mean that this number will be found!
- frequency unit
- The unit for formant frequency display. This field is ignored if the formant tracks are plotted in the spectrogram graph.
- multiple colors
- If checked, each formant is drawn in a different color (as defined in the color scheme's function line colors). Note that the first color is defined by the Line number.
- Selects the type of spectrum to be used for peak detection. The methods cepstrum smoothing and lpc transfer function are implemented.
- number of coefs.
- Number of cepstrum or lpc coefficients. If this value is set to
0, the number of coefficients is set to the sampling frequency in kHz + 4 (e.g. sampling frequency = 16kHz, no. coefs = 20, sampling frequency = 44kHz, no. coefs. = 48).
- The factor for the preemphasis filter when using the lpc method (Any value between 0 and 1).
- If checked, the tracking algorithm is enabled, otherwise only peak detection is performed.
- bias frequency
- A bandwidth-like frequency value used in the tracking algorithm to assign peaks to a formant track.
- min. duration
- Minimum length of a part of a formant track in frames. All parts with a shorter duration are removed by the tracking algorithm.
- voiced only
- This feature is not yet implemented, but if checked, only formant tracks in voiced parts of the signal would be assigned.