تجزیه و تحلیل هدف گرم شدن صوتی با ارجاع ویژه به عوامل موثر ارگونومیک

Vocal warm-up was studied in terms of changes in voice parameters during a 45-minute vocal loading session in the morning. The voices of a randomly chosen group of 40 female and 40 male young students were loaded by having them read a novel aloud. The exposure groups (5 females and 5 males per cell) consisted of eight combinations of the following factors: (1) low (< 25 ± 5%) or high (> 65 ± 5%) relative humidity of ambient air; (2) low [< 65 dB(SPL)] or high [> 65 dB(SPL)] speech output level during vocal loading; (3) sitting or standing posture during vocal loading. Two sets of voice samples were recorded: a resting sample before the loading session and a loading sample after the loading session. The material recorded consisted of /pa:ppa/ words produced normally, as softly and as loudly as possible in this order by all subjects. The long /a/ vowel of the test word was inverse-filtered to obtain the glottal flow waveform. Time domain parameters of the glottal flow [open quotient (OQ), closing quotient (CQ), speed quotient (SQ), fundamental frequency (F0)], amplitude domain parameters of the glottal flow [glottal flow (fAC) and its logarithm, minimum of the first derivative of the glottal flow (dpeak) and its logarithm, amplitude quotient (AQ), and a new parameter, CQAQ], intraoral pressure (p), and sound pressure level (SPL) values of the phonations were analyzed. Voice range profiles (VRP) and the singer's formant (g/G, a/A, c1/c, e1/e, g1/g for females/males) of the loud phonation were also measured. Statistically significant differences between the preloading and postloading samples could be seen in many parameters, but the differences depended on gender and the type of phonation. In females the values of CQ, AQ, and CQAQ decreased and the values of SQ and p increased in normal phonations; the values of fAC, dpeak, and SPL increased in soft phonations; the values of AQ and CQAQ decreased in loud phonations; the harmonic energy in the singer's formant region increased significantly at every pitch. In males the values of OQ and AQ decreased and the values of dpeak, F0, p, and SPL increased in normal phonations; the values of fAC and p increased in soft phonations. The changes could be interpreted as signs of a shift toward hyperfunctional voice production. Low humidity was associated with more hyperfunctional changes than high humidity. High output was associated with more hyperfunctional changes than low output. Sitting position was associated with an increasing trend at both margins of male VRP, whereas the case was the opposite for standing position.

Vocal loading is defined as prolonged use of the voice. Vocal warm-up (WU) can be described as “an initial period of rapid vocal change”1 that takes place during vocal loading. In general, it is believed that after WU voice use becomes easier and smoother. The phenomenon can be seen during vocal loading in both speech 1, 2 and 3 and singing.4 Empirically, WU can also be achieved by specific vocal exercises, which are considered to be an important part of preparation not only for singing but also for speaking performances. 5 and 6 As to the physiological mechanisms underlying the subjective experiences on vocal WU, there is very little specific knowledge. An attempt to understand its background was made by Elliot et al.6 However, the method used (measurement of phonatory threshold pressure) failed to show any systematic changes and the interindividual variation was large. The authors rejected the hypothesis that viscoelastic changes of the vocal muscle would be responsible for the phenomenon. However, it is not clear how the pretest voice use was controlled, and it is possible that the baseline level was not the same for all subjects. On the basis of our earlier studies on vocal loading, the choice of the reference level, that is, the pretest state of voice, considerably affects the outcome.7, 8, 9 and 10 As Neils and Yairi11 pointed out, a large number of normal subjects would be required to improve our understanding of WU due to the marked intersubject variation. To overcome this problem, a relatively large number of subjects (40 female and 40 male students) were recruited for our study. The collection of speech samples started in the morning, that is, the baseline represents vocal quality prior to any significant voice use. The present study was launched because several parameters of the glottal flow [fundamental frequency (F0), intraoral pressure, sound pressure level (SPL), glottal flow, negative peak amplitude of the differentiated glottal flow (dpeak), open quotient (OQ), speed quotient (SQ), and closing quotient (CQ)] did not change monotonously in a day-long loading experiment in our earlier studies.7, 8, 9 and 10 Instead, these parameters revealed nonlinearity, with marked changes after the first 45-minute loading session as well as after the lunch break. The present study focused on the changes occurring during the first loading session in the morning rather than on general loading changes. All the data were reanalyzed, and new, previously unpublished results were included. It was assumed that the changes (see above) occurring during the first vocal loading session in the morning would be mostly caused by the WU effect. This assumption seems tenable for five reasons: (1) The biggest changes in the objective voice parameter values took place during the first 45-minute loading session.7, 8, 9 and 10 No such major changes were seen in the voice samples obtained later during the day. This finding is consistent with the definition of vocal WU as an initial period of rapid vocal change (see above). (2) In the previous studies, the vocal loading time needed for subjective vocal WU effects to take place has varied between 5 and 45 minutes.1, 2 and 3 Based on these observations, 45 minutes should be a sufficient loading time for the WU phenomenon to appear. (3) According to the earlier studies, the positive effects of WU last for much longer than 45 minutes when the loading is continued.1 and 3 Therefore, it was unlikely that marked negative effects would occur during the first 45 minutes of loading. (4) Vocal fatigue was not likely to take place during the first loading session in the morning, because the loading task (reading a novel) was not considered especially strenuous by the subjects; actually, subjective signs of vocal fatigue occurred later during the test day (this issue will be discussed in another paper). In the study by Neils and Yairi,11 too, a 45-minute reading period in the morning caused no clear signs of fatigue even at output levels as high as 70 and 90 dB(A). (5) The subjects arrived at 8.00 View the MathML source They had probably done their normal morning routines, including breakfast and travel to the test place. The time of beginning to produce the first voice samples (8.45 View the MathML source) was about the same as the usual time of beginning lessons at the university. We therefore assumed that any marked nonspecific morning hoarseness would already be gone by the time we began to record the first voice samples. The findings of a previous study without vocal loading12 also point to that direction: no directly time-dependent changes in the F0 values or sound levels in normal oral reading samples between 9.15 and 11.10 AM could be seen in 60 normal male subjects. On the basis of these five reasons, it was assumed that the first 45 minutes of vocal loading would be sufficient for the vocal WU to take place and, on the other hand, sufficiently short to prevent any marked vocal fatigue. In real-life speaking situations, the speaker is faced with various environmental or ergonomic factors affecting the vocal apparatus. Three such factors in various combinations were therefore included in the analyses. The factors were the following: (1) Humidity of air (dry and humid). Many studies suggest that ambient air humidity affects various voice parameters.7, 8, 13 and 14 (2) Reading output level (low and high). Variation of the reading output level was used to simulate the effects of background noise on voice production.15 (3) Reading posture (sitting or standing). To the best of our knowledge, there are only two earlier studies on the significance of reading posture for voice production.7 and 8 Reading posture and ambient humidity are typical ergonomic factors. Reading output level is not an ergonomic factor itself, but its usual cause in real life, the background noise, is an ergonomic factor. For the sake of simplicity, these three factors studied will be called “ergonomic factors” in this paper. The WU effect was analyzed by parameterizing the changes in the glottal volume velocity waveform using both time domain and amplitude domain parameters. In addition, speech samples were quantified by measuring values for both sound pressure level (SPL) and intraoral (subglottal) pressure. Finally, voice range profiles representing the speaking voice range and the singer's formant of the loud phonation were determined.

In conclusion, it can be stated that vocal WU affects many aspects of voice production in both females and males. In addition, the WU phenomenon is affected by various environmental and ergonomic factors implicit in the work of voice and speech professionals. Considering all WU changes, WU actually shifted the voice production toward the hyperfunctional direction, or even reflected slight hyperfunctioning. It is hoped that the analysis of subjective voice complaints during loading, which is under way, will help to shed light on this result. For instance, it will be interesting to see whether subjects showing more changes toward hyperfunctioning will also report more fatigue, poor motivation, discomfort in the throat, etc., after the loading period compared to others. There were several occasions where the ergonomic factors had a significant influence on WU changes. Ambient humidity affected more parameters than the other two factors in the female subjects. In the male subjects, the output level and posture during loading had effects on more parameters than humidity. Of all the three ergonomic factors, ambient humidity is the only one that already affected the subjects before the test. The ergonomic factors, especially ambient humidity, also had interesting effects on the overall levels of some parameters. This issue is too complex to be discussed here and may deserve further investigation. Briefly, there may be seasonal variation in vocal functions. All in all, it seems necessary to standardize the ergonomic factors as well as the pretest state of voice usage between the subjects before tests aiming to assess minor changes in voice source parameters.