Download xassp User's Manual (Advanced Speech Signal Processor under the

5.3. FORMANT ANALYSIS
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maxFzero: the highest F0 to be evaluated (default 600 Hz). Decreasing maxFzero
speeds up processing. However, since fewer potential periodicity markers will
be evaluated, it may lead to voicing errors. Decreasing maxFzero may be necessary to suppress an octave error. Contrary to most other F0 analyses, maxFzero
should not be set to slightly above the correct F0 but rather to slightly below
its octave (i.e. the lowest erroneous value). Increasing maxFzero slows down
processing, may in some cases give somewhat better results, but may also lead
to octave errors.
noiseAmp: the amplitude threshold for an extremum to be considered a potential period marker (default 16 at 16 bit signal resolution). Extrema with amplitudes
below this threshold are assumed to be due to background noise or weak unvoiced signals. Decreasing noiseAmp slows down processing and may in some
cases lead to erroneous detection of periodicity in noisy stretches. Increasing
noiseAmp speeds up processing but has no deteriorating effect on the results as
long as it is lower than the actually lowest extremum in voiced stretches.
frameShift: determines the rate at which F0 values are produced at the last stage,
namely once per frameShift ms. The default value is 10 ms for proper alignment with other analysis data, such as energy contours. Decreasing frameShift
may in extreme cases lead to gaps in the F0 track. These may, for example,
be caused by a phase shift in the transition from a vowel to a nasal. Note that
frameShift may be reduced to one sample, because the F0 values are determined
at the sampling rate of the signal. Increasing frameShift mainly results in the
voicing boundaries becoming increasingly inaccurate. Very short stretches that
were declared unvoiced (e.g. in the occlusion of lenis plosives) may therefore
disappear because the frames extending over such stretches now contain more
voiced samples, resulting in the frames becoming declared voiced.
5.3 Formant Analysis
If an LPC spectrum is selected in Section, a formant analysis may be invoked. In this
analysis, local peaks are searched in the LPC spectrum. By parabolic interpolation
through the three adjacent FFT points that define such a peak, the peak frequency, its
bandwidth and amplitude are estimated. These values will be listed in a dialog box
and may be logged in a file. How many peaks will be searched for, can be defined in
the section pop-up menu under Formants. There, you will also find a toggle button
for switching formant calculation on or off. The formant data will continuously be
updated with a change in the spectrum in the section window.
When analysing formants, you are advised not to set the number of FFT points to
auto (or 0) because this would result in the formant data becoming dependent on the
width of the Section display window. The number of FFT points should rather be set
such that a spectral resolution of between 20 and 50 Hz is obtained (e.g. 512 for a