Acoustic Correlates of Glottal Opening in German Obstruent Production Michael Jessen Bundeskriminalamt, Department of Speaker Identification and Tape Analysis, Wiesbaden, Germany E-mail: [email protected] hence leading to earlier termination of glottal adduction. ABSTRACT The glottal opening and voice quality behavior of aspirated stops and voiceless fricatives are also compared For the first five vowel periods after aspirated/voiceless to the influence of the unaspirated stop and voiced and unaspirated/voiced stops/fricatives in German the fricative cognates. Less dramatic voice quality changes are degree of glottal opening based on transillumination was expected with these sounds, since glottal opening is measured simultaneously with the acoustic voice quality probably very small at best. However, it is possible, that parameters H1-H2, H1-A1, H1-A3 (in order to capture some amount of glottal opening is induced passively due breathy phonation and glottal leakage) and with f0. A to aerodynamic factors [9] and that small glottal gradual decrease in glottal opening and the voice quality abductions of this kind influence the voice quality early in values was observed after aspirated stops and voiceless the following vowel. Another possibility is that fricatives, usually with an earlier-timed reduction in the physiological settings required to enhance voicing in case of the fricatives than the stops. Slight glottal opening obstruent production have an influence on voice quality. and vq-value reductions were observed after unaspirated One hypothesis to be investigated in particular is that stops, probably resulting from aerodynamically- vocal fold slackening, which enhances obstruent voicing, conditioned passive glottal opening. Higher vq-values leads to a certain amount of glottal leakage that were found after voiced fricatives than unaspirated stops. coarticulates into the following vowel. This is hypothesized to be a consequence of increased glottal leakage due to vocal fold slackening employed to 2. METHOD maintain obstruent voicing, which in German is phonologically required for voiced fricatives such as /v/ A set of words containing the aspirated stops /p,t/ and the but not for unaspirated stops such as /b/. unaspirated stops /b,d/, as well as the voiceless fricatives /f,s/ and voiced fricatives /v,z/ were produced by a male 1. INTRODUCTION speaker of German. (In German the phonemic distinction between /p,t/ and /b,d/ is more consistently and saliently The production of aspirated stops and voiceless fricatives implemented as aspirated vs. unaspirated than as voiceless in languages like English, Swedish, and German leads to vs. voiced, respectively; cf. [6].) certain amounts of breathy phonation in the adjacent vowels [e.g. 1,2,3,4,5,6]. It is commonly assumed that aerodynamic indices of breathy voice such as high open quotient [1,2] or acoustic indices such as high H1-H2 or H1-A1 [3,4,6] in vowels preceding or following aspirated stops and voiceless fricatives are a coarticulatory effect that is due to the fact that glottal abduction can begin before vowel offset and glottal adduction can end after vowel onset, respectively. Yet, there is very little empirical data available where glottal opening and voice quality induced by obstruents have been compared directly [cf. 1]. In the present study glottal opening behavior and acoustically measured voice quality are studied at the onset portion of vowels following aspirated stops and voiceless fricatives. By comparing these groups of sounds it is possible to investigate how coarticulatory voice Figure 1: Audio waveform (upper signal display) and quality is influenced by patterns of oral-laryngeal smoothed transillumination signal (lower signal display) at coordination. For example, it is shown by [1] that after boundary between /p/ and /i/ with labels for the first five voiceless fricatives breathy voice reduces sooner than after vowel periods (lowest window). aspirated stops. They explain this result by the fact that the glottal opening gesture is coordinated earlier with respect The target obstruents occurred in two types of context, to vowel onset in voiceless fricatives than aspirated stops, word-medial position between stressed and unstressed vowel and word-initial position before stressed /i/ -450 preceded by a carrier word ending in a vowel, and were /p/ Glottal Opening -500 produced about 20 times each in both contexts. -550 Transillumination (TI) was used to study glottal opening -600 behavior in obstruent production [cf. 6 for more details -650 and data involving the TI recording on which this study is /b/ based; the present results are from the first recording -700 session]. For each of the first five vowel periods after the -750 p1 p2 p3 p4 p5 target obstruent fundamental frequency and voice quality p1 p2 p3 p4 were measured in the audio signal, and for the same five 8 H1-H2 temporal locations glottal opening degree was measured 6 on the basis of the smoothed TI curve (see Fig. 1). The 4 voice quality parameters investigated are H1-H2, H1-A1, 2 and H1-A3 (amplitude of first harmonic minus amplitudes 0 of second harmonic, first formant, and third formant, -2 respectively). They were measured on the basis of DFT -4 spectra with a 25.6 ms Hamming window centered around -6 p1p1 p2 p3 p4 p5 each of the five vowel periods. H1-H2 and H1-A3 were chosen because high values of these parameters are known 8 H1-A1 as correlates of breathy voice or glottal leakage [e.g. 7]. Physiologically, high H1-H2 is a correlate of high open 4 quotient, and high H1-A3, as a measure of increased 0 spectral tilt, reflects a closing portion of the glottal cycle -4 of relatively long duration and reduced skewness [8]. H1- -8 A1 was included because this parameter has been used -12 successfully in some relevant studies [3] and because it p1 p2 p2 p3 p3 p4 p5 has been claimed that H1-A1 is a correlate of glottal opening degree [8]. Indeed, correlations between degree of H1-A3 glottal opening and the three voice quality parameters, 14 calculated word-medially across aspirated stops and 10 voiceless fricatives and across all five vowel periods, turn out to be slightly higher for H1-A1 (0.785) than for H1-H2 6 (0.766) and lowest for H1-A3 (0.638). Corrections 2 proposed by [7,8] (H1*-H2*, H1*-A1, H1*-A3*) were -2 applied but the resulting obstruent-induced patterns differ p1 p2 p2 p3 p3 p4 p5 only little from those of the uncorrected voice quality values. Furthermore, H1*-H2* could not be determined 155 f0 for the vowel [i]. For these reasons only the results for 150 uncorrected H1-H2, H1-A1, and H1-A3 are reported. 145 140 3. RESULTS 135 Unless mentioned otherwise the results presented in this 130 section are from word-medial position. In most respects p1 p2 p3 p4 p5 the patterns in word-initial context are essentially the Figure 2 (from top to bottom): Glottal opening (y-axis in same. Fig. 2 (top graph) shows that after the aspirated stop arbitrary units), H1-H2, H1-A1, H1-A3 (y-axis in dB), and there is a gradual decline in glottal opening from vowel f0 (in Hz) for first five periods (x-axis) into unstressed onset until (at least) the fifth period, indicating the final schwa after aspirated (gray squares) and unaspirated stages of the glottal opening gesture associated with stop (black circles) labial stop (average across about 20 aspiration. Glottal opening of the unaspirated stop is repetitions). Periods with significant aspirated-unaspirated significantly lower than after the aspirated stop for all differences (p < 0.05) are marked by gray shading. periods except the final one. Even the unaspirated stop shows a slight decrease in glottal opening, probably resulting from slight passive glottal abduction induced by These glottal opening and voice quality dynamics after buildup of intraoral air pressure [cf. 9]. The three voice aspirated and unaspirated stops in German are consistent quality parameters H1-H2, H1-A1, and H1-A3 show quite with the results on German by [3; see their Fig. 9, whereby a similar pattern as the glottal opening gesture, with a L0=H1 and L1=A1] and with the results on the Swedish gradual lowering of values – indicating decreasing levels and most of the English speakers reported in [1, 2; see in of breathy voice into the vowel – and with higher values particular the TI data in 1 and the open quotient data in after the aspirated than the unaspirated stop. 1,2]. opening pattern is practically the same. However, a -450 Glottal Opening different situation occurs when comparing aspirated stop -500 /f/ and fricative at alveolar place of articulation. In that case, -550 not only H1-H2 but also glottal opening decreases sooner -600 after the fricative than the stop, which is shown in Fig. 4. -650 Lower H1-H2 after /s/ than /t/ is also found in English [4] -700 /v/ and German [evaluation of raw data in 6]. -750 p1p1 p2 p3 p4 p5 -450 Glottal Opening -500 /t/ 8 H1-H2 -550 6 -600 4 -650 2 /s/ -700 0 -2 -750 -4 p1p1 p2 p2p3 p3 p4 p4 p5 p5 -6 p1 p2p3 p3 p4 p4 p5 8 H1-H2 6 8 H1-A1 4 2 4 0 0 -2 -4 -4 -6 -8 p1p1 p2 p3 p4p5 p5 -12 Figure 4: Glottal opening (upper) and H1-H2 (lower) for p1 p2 p3 p4 p5 p5 first five periods into unstressed schwa after aspirated alveolar stop (gray squares) and voiceless alveolar H1-A3 14 fricative (black circles) (cf. Fig. 2 for further conventions). 10 The most striking difference between stops and fricatives, 6 as shown in Figs.