Title of the article

4.Method

To find out whether people indeed prefer triplet patterns in allegro speech, we ran a pilot experiment in which we tried to elicit fast speech. Six subjects participated in a multiple-choice quiz in which they competed each other in answering twenty simple questions as quickly as possible. In this way, we expected them to speak fast without concentrating too much on their own speech. In Table 3 one of the quiz items is depicted.
Table 3. Quiz item

Q4 President Bush is een typische ‘President Bush is a typical ’

A1 intellectueel ‘intellectual’

A2 amerikaan ‘American’

A3 taalkundige ‘linguist’
We categorized the obtained data as allegro speech. As a second task the subjects were asked to read out the answers at a normal speaking rate embedded in the sentence ik spreek nu het woord … uit 'now I pronounce the word … '. This normal speaking rate generally means that the subjects will produce the words at a rate of approximately 180 words per minute, which we categorize as andante speech. All data were recorded on minidisk in a soundproof studio and normalized in CoolEdit in order to improve the signal-noise (S/N) ratio. Normalizing to 100% yields an S/N ratio approaching 0 dB.

Six trained listeners judged the data auditively and indicated where they perceived secondary stress. After this auditive analysis the data were phonetically analyzed in PRAAT (Boersma and Weenink, 1992). We compared the andante and allegro data by measuring duration, pitch, intensity, spectral balance and rhythmic timing (Sluijter, 1995; Couper-Kuhlen, 1993; Cummins & Port, 1998; Quené & Port, 2002; a.o.). Sluijter claims that, respectively, duration and spectral balance are the main correlates of primary stress. In our experiment, we are concerned with secondary stress.

For the duration measurements, the rhymes of the relevant syllables were observed. For example, in the allegro style answer A2 amerikaan in Table 3, we measured the first two rhymes and compared the values in Msec. with the values for the same rhymes at the andante rate. In order to make this comparison valid, we equalized the total durations of both realizations by multiplying the duration of the allegro with a so-called 'acceleration factor', i.e. the duration of the andante version divided by the duration of the allegro version. According to Eefting and Rietveld (1989) and Rietveld and Van Heuven (1997), the just noticeable difference for duration is 4,5%. If the difference in duration between the andante and the allegro realization did not exceed this threshold, we considered the realizations as examples of the same speech rate and neglected them for further analysis.

For the pitch measurements, we took the value in Hz in the middle of the vowel. The just noticeable difference for pitch is 2,5% ('t Hart et al, 1990). For the intensity measurements, we registered the mean value in dB of the whole syllable.

The next parameter we considered concerns spectral balance. Sluijter (1995) claims that the spectral balance of the vowel of a stressed syllable is characterized by more perceived loudness in the higher frequency region, because of the changes in the source spectrum due to a more pulse-like shape of the glottal waveform. The vocal effort, which is used for stress, generates a strongly asymmetrical glottal pulse. As a result of the shortened closing phase, there is an increase of intensity around the four formants in the frequency region above 500 Hz. Following Sluijter (1995) we compared the differences in intensity of the higher and lower frequencies of the relevant syllables in both tempos.

Finally, we considered rhythmic timing. The idea is that the beats in speech are separated from each other at an approximately equal distance independent of the speech rate. In other words, a speaker more or less follows an imaginary metronome. If he/she speaks faster, more melodic content will be placed between beats, which results in a shift of secondary stress. This hypothesis will be confirmed if the distance between the stressed syllables in the andante realization of an item, e.g. stu and toe in studietoelage, approximates the distance between the stressed syllables in the allegro realization of the same item, e.g. stu and la. If the quotient of the andante beat interval duration divided by the allegro beat interval duration approximates 1, we expect perceived restructuring.