Ling520 - Fall 2008 - Lab 3

The pupose of this lab is to ensure that you have a practical understanding of the concepts of frequency, period and wavelength, as related to speech sounds and as seen in time waveforms, spectral slices, and spectrograms.

1. Materials

In the files a1.wav, a2.wav, a3.wav, a4.wav, a5.wav, a6.wav, you'll find six short and simple utterances, each consisting of a more-or-less stable vowel produced at a more-or-less constant pitch. In the file SA1.WAV, you'll find a short sentence from the TIMIT database.

Download these files into a convenient local directory to work on, and play them so that you know what you're dealing with.

2. What to do

For each of the six files a1-6.wav, read the file into Praat, and:

a. Determine the fundamental frequency of the syllable (at some representative place in the middle) by four different methods:

i. Measure several pitch periods (taken together) in the time waveform, and convert to frequency. (The reason to measure several pitch periods is to make the consequences of measurement uncertainty smaller -- try comparing measurements of individual pitch periods.) If you don't know what "pitch periods" look like, expect to learn this in the lab session, or ask about it -- and similarly for other analysis methods cited below.

ii. Make a narrow-band spectrogram, find the fundamental frequency, and measure it. [Note: For a narrow-band spectrogram, you want 3-5 pitch periods to fall within the analysis window, and you want to measure frequencies in the range of 50 to a few hundred Hz.; thus a good choice of options in Praat's edit window for this might be Spectrum>>Spectrogram settings>> (Window length = .04, View range = 0 to 1000). You might want to decrease the dynamic range somewhat as well.]

iii. Make a spectral slice over an appropriate window, and measure the frequency of some prominent higher harmonic (5th, 10th, whatever). [Note: choose the "appropriate window" to cover about 4-6 pitch periods, by selecting the region in the waveform display; get the spectral slice from Spectrum>>View spectral slice; zoom in on about the lowest 1,000 Hz of the spectrum, e.g. by selecting that region with the mouse and clicking on the "sel" button]

iv. Use Praat's built-in pitch tracker. [Note that you may want to adjust the display via Pitch>>Pitch settings>>Pitch range.]

b. Determine the first, second and third formant frequencies during the same region of time as your pitch determination, using three different methods:

i. Make a wide-band spectrogram and estimate the formants from looking at it. [Note: for a wide-band spectrogram, you want the analysis window to be about half a pitch period; so in this case .005 would be a good choice of Window length; and you want to measure formant frequencies of about 300 to 3500 Hz, so that 0 to 3500 might be a good choice of View Range.]

ii. Make a spectral slice over an appropriate window, and measure the formants in it.

iii. Use Praat's built-in formant tracker.

What periods correspond to the frequencies of the first and second formants? Can you find evidence of oscillations at those frequencies in the time waveform?

c. Now read in the file SA1.WAV.

Choose three syllables in the phrase, and perform the same analysis of F0, F1, F2 and F3 -- by the same methods -- as for the six isolated vowels. How much difference does it make where in the syllable you choose to analyze?

3. What to hand in

A document with screenshots from Praat showing your work, with any appropriate additional commentary.