The number of 'poles' that this algorithm computes is twice the Maximum number of formants that's why you can set the Maximum number of formants to any multiple of 0.5). For each analysis window, Praat applies a Gaussian-like window, and computes the LPC coefficients with the algorithm by Burg, as given by Childers (1978) and Press et al. After this, pre-emphasis is applied with the algorithm described at Sound: Pre-emphasize (in-place). The sound will be resampled to a sampling frequency of twice the value of Formant ceiling, with the algorithm described at Sound: Resample. See the source-filter synthesis tutorial for a technical explanation, and Sound: Pre-emphasize (in-place). The point of this is that vowel spectra tend to fall by 6 dB per octave the pre-emphasis creates a flatter spectrum, which is better for formant analysis because we want our formants to match the local peaks, not the global spectral slope. If this value is 50 Hz, then frequencies below 50 Hz are not enhanced, frequencies around 100 Hz are amplified by 6 dB, frequencies around 200 Hz are amplified by 12 dB, and so forth. The +3 dB point for an inverted low-pass filter with a slope of +6 dB/octave. This is comparable to the bandwidth of a Hamming window of 0.025 seconds, which is 1.303 / (0.025 s) = 52.1 Hz, but that window (which is the window most often used in other analysis programs) has three spectral lobes of about -42 dB on each side. This window has values below 4% outside the central 0.025 seconds, and its frequency resolution (-3 dB point) is 1.298 / (0.025 s) = 51.9 Hz, as computed with the formula given at Sound: To Spectrogram. For instance, if the Window length is 0.025 seconds, the actual Gaussian window duration is 0.050 seconds. The actual length is twice this value, because Praat uses a Gaussian-like analysis window with sidelobes below -120 dB. The effective duration of the analysis window, in seconds. You may like to experiment with this setting on steady vowels. analysing an as having a single formant near 500 Hz whereas you want two formants at 300 and 600 Hz.

If you choose a too high ceiling, you may end up with too few formants in the low frequency region, e.g. These are just examples there is large variation between speakers, and Escudero, Boersma, Rauber & Bion (2009) showed that the vocal tract length difference between a person's front vowels and their back vowels may be greater than the average vocal tract length difference between males and females. An average adult female speaker has a vocal tract length that requires an average ceiling of 5500 Hz (which is Praat's standard value), an average adult male speaker has a vocal tract length that requires an average ceiling of 5000 Hz, and a young child may have a vocal tract length that requires an average ceiling of 8000 Hz. It is crucial that you set this to a value suitable for your speaker. The maximum frequency of the formant search range, in hertz. Otherwise, the Maximum number of formants can be any multiple of 0.5, you can choose 4, 4.5, 5, 5.5, 6, and so on (see below). in terms of vowel height (F1) and vowel place (F2). This, in combination with the Formant ceiling setting, is the only way in which this procedure will give you results compatible with how people tend to interpret formants for vowels, i.e. If you set the time step to 0.0 (the standard), Praat will use a time step that is equal to 25 percent of the analysis window length (see below).įor most analyses of human speech, you will want to extract 5 formants per frame. The actual number is somewhat lower (usually 195), because we cannot measure very well near the edges. If the sound is 2 seconds long, and the time step is 0.01 seconds, there will be approximately 200 analysis frames. The time between the centres of consecutive analysis frames. It performs a short-term spectral analysis, approximating the spectrum of each analysis frame by a number of formants. A command that creates a Formant object from every selected Sound object.

Praat formant extration code