Essay on Linear Prediction Analysis and Spectrographic Depiction

1736 Words 7 Pages
In general, recent studies make use of two methods for estimating formant patterns of vowel sounds: Linear prediction analysis (LP analysis, or synonymously, linear predictive coding [LPC]), and spectrographic depiction. Moreover, many studies link these two methods together, that is, calculation of numerical values of frequencies, bandwidths, and amplitudes of the formants is carried out by LP analysis, and these values are crosschecked by visual inspection of the related spectrogram.
LP analysis relies on the source-filter theory of speech production. Simply put, it is based on a decomposition of a sound wave into a source and a filter, where the filter shape is assumed to correspond to the vocal tract resonances. As a result, values
…show more content…
Thus, a low value leads to higher number of analysis frames. (2) A maximum number of formants, which determines the number of expected formants in the calculated spectrum, which are represented in the calculation in form of filter poles. (3) A frequency ceiling (in Hz) for the range of formant estimation. (4) A window length that determines the effective duration (in s) of the analysis window. (5) A formant bandwidth, which determines the frequency range of a single formant frequency. (6) A cut off frequency for pre-emphasis (in Hz; 6 dB amplitude enhancement per octave above this frequency).
In the case of ‘To LPC…’ and its sub-commands, the so-called Nyquist frequency, which is equal to half the sampling frequency of the particular signal, is automatically used as their frequency ceiling for formant estimation. Therefore, this requires (in most cases) resampling the sound before doing an analysis. This is necessary, because estimation of, for example, five formants below 5500 Hz requires a sampling frequency of 11 kHz (for more details regarding sampling frequency values and sub- commands of ‘To LPC…’ see PRAAT manual).
Among the ‘To Formant…’ commands, there are several algorithms that can be used for formant estimation: (1) ‘To Formant (sl)…’, which is based on the implementation of the Split Levinson algorithm by Willems (1986) that will always find the

Related Documents