Linguistics 580
General Phonetics

Vowel Duration Experiment

Goal

In this exercise, you will measure the acoustic durations of vowels to see how their duration is affected by two contextual factors:

(1) the voicing of the following consonant
(2) presence vs. absence of a following phrase (sentence) boundary

You will do this by examining acoustic waveforms and using the cursor to select the interval that begins at the release of the word-initial consonant closure and ends at the achievement of closure for the word-final consonant.

Method

You will be using Praat for this exercise. There are three individual files that can be downloaded from here: (Set1.aiff, Set2.aiff, Set3.aiff).. Each contains one repetition of the following six utterances :

1. I gave a duck to Doug.
2. I looked in the cab for a cap.
3. It's got to be tight to be tied.
4. I found the cap in the cab.
5. I gave Doug a duck.
6. It's got to be tied to be tight.

Follow this procedure to do the measurements:

(1) Double-click on one of these files (e.g., Set1.aiff) to begin. This should open Pratt, and and Sound Set1 will appear in the list of Praat objects.

(2) Select the Sound Set1 object and click on Edit.

(3) If you see a spectrogram as well as waveform the Edit window, select the View menu and de-select Show Analyses.... Uncheck Show Spectrogram. You will not need the spectrogram for this exercise

(3) Select the portion of the waveform that looks like it corresponds to the first sentence, and click on the play bar to hear it. If you have it, then click on the sel button on the bottom left of the Edit window to zoom the display to just that selection.

(5) Now zoom the display again so as to include an interval just a bit larger than the vowel in the word you are measuring, so that you can clearly see (and hear) the release of the word-initial consonant, and the onset of closure of the word-final consonant. When you have selected the appropriate interval, click on the sel button again.

(6) Now select the interval beginning just at the instant of initial consonant release, and ending at the achievement of final consonant closure. Aspiration, if any, will therefore be included in this interval. The duration of the selected interval (in seconds) can be found in the box just above the selected section of the waveform. Figure 1 shows this for the acoustic vowel segment in duck--utterance 1/Set1. Note that it has a duration of about 108 milliseconds.

Enter the duration of each vowel (to the nearest millisecond) in the appropriate place on the attached worksheet. To go on to the next vowel clicking on the out button a couple times, to zoom the display out. Find the next vowel and repeat the procedure.

Tabulation, plotting and interpretation

After all sets have been measured, compute the average duration of the vowel across the three repetitions. You should end up with twelve means (see worksheet): three different vowels, each of which is produced with either a voiced or voiceless final consonant, and each of which occurs sentence-medially and sentence-finally. (That is, you will find the average duration of the vowel in duck in medial position and then in final position, and then for Doug and so on. )

Once you have computed the twelve means, plot the means as bars in the appropriate places on the attached graph templates. On the basis of these graphs, answer the following questions:

(1) How is the length of a vowel affected by the voicing of the following consonant?
Is the effect comparable for all three vowels?

(2) How is vowel length affected by the position of the word in the sentence?

Is the effect comparable for all three vowels?

(3) What is the interaction between sentence position and voicing (i.e. is the effect of the consonant of greater magnitude in final position, is it less, of no consequence...)?