AbstractPirith isbelieved as a protective doctrine preached by the Load Buddha in Pali language. The aim of this study isto analyze acoustic properties of Pirithusing computer-aided methods and identify special characteristics and patterns.In this study, two methods were used to identify special characteristics of Angulimala Sutta. First method calculatesvoiced to unvoiced ratio using zero crossing rate and energy content associatedwith the acoustic signal while second method recognizes vowel distributionusing first and second formant frequencies. Resultsof the first method indicates approximately 96% of frames are voiced while thesecond method suggests approximately ofvowels concentratein the square region of and demonstrating whenchanting the Angulimala sutta most of the time the tongue height is low positioned in back levels while lipsshaped unroundedKeywords: Formant frequencies,Voiced to unvoiced ratio, Zero-Crossing rate, Vowel distributionIntroductionSpeech productionprocess begins at the point of converting an idea developed in the speakers’mind to a language code. With the aid of articulatory motion and vocal tractmovement, the phonemes which are lined up in a set of sequences propagateoutside as an acoustic waveform.
“Pirith”means protection from all aspects and this protection is to be obtained byreciting or listening to Pirith suttas.The practice of reciting and listening to Pirithsuttas began very early in the history of Buddhist culture. As reported byJayaratne 2007, an experiment was performed at Kanduboda InternationalMeditation Centre, Sri Lanka to understand the effect of Pirith on human beings. When a sample of human subjects was allowedto listen to Pirith chants, it isobserved that within minutesof the commencement of the chanting, their heart beat reduced, heart pulse amplitudehalved and reached to an alpha state similar to what is obtained under ameditative trance. Voiced to unvoiced ratio (V/UV ratio) is animportant parameter as it indicates the involvement of speech production systemwith vibration of vocal codes. In this work, we combined the results of V/UVratio with zero crossing rate (ZCR) and energy of short time segments of thesignal to strengthen the analysis.
In voiced speech, thevibrating glottis generates periodic pulses which are resonate in the vocal tract.Therefore, when vowels are pronounced similar frequencies are generated.However, in the unvoiced speech, vocal chords held open and a continuous airbeam flow through them. The air beam turns into a turbulent flow because ofnarrowed vocal tract and it creates, non-periodic, noise-like sounds 8.
The zero crossing rate measures numberof intersections a given signal makes with the time axis per unit time in anamplitude-time plot. Voiced speech shows a lowzero-crossing rate due to the excitation of vocal tract by the periodic airflow, whereas the unvoiced speech shows high zero-crossing count as it isproduced by the turbulent airflow flowed through the narrowed vocal tract 1.Additionally, the voiced part of the speech has high energy content because ofits periodicity. According to the acoustic theory of speech production, vocaltract is modeled as a non-uniform tube closed at vocal folds and open at thelip end 9. Cross sectional area ofthe vocal tract depends on the position of tongue, lips, jaw and velum. Due to varyingcross section along the vocal tract, different resonance frequencies(harmonics) are generated in response to varying vocal fold vibrations.
Consequently, the complex output voice signal is composed of several harmonicscalled as formants which are clearly visible in spectrographic displaysof voice segments. Normally, they occur on average at intervals of , where c is the speech ofsound and the lengthof the vocal tract 3. Vowels can be mapped using therelationship between lip opening widthto the first formant frequency, and tongue constriction width to secondformant frequency, Cardinalvowels, which are not of any particular language but a measuring system indescribing sounds of languages are used as a set of reference vowels in thiswork. These vowel sounds demonstrate if the tongue is in an extreme position,either front or back, high or low.
The current system was modified by DanielJones * based on the original idea proposed by earlier phoneticians, notablyEllis** and Bell.**. The standard International Phonetic Alphabet, IPA voweltrapezium, is shown in figure (*).MethodologyInthe analyzing process, Samples ofAngulimala Sutta recited bymale monk chanters were recorded under high precision conditions and 15 sampleswere subjected to analysis. Voiced recording was then subjected tosplitting of smaller voiced segments of frame length using sampling rate of . This specific frame length was selectedas vocal tract has fixed characteristics over a time interval of the order of Voiced to unvoiced ratio is calculated bycounting number of frames less than a reference zero-crossing rate and higherthan a reference short time energy as voiced frames and others as unvoicedframes according to the algorithm shown in Figure 1. In the computational speech model, apre-emphasis filter is applied to the sampled time series of voiced segment tocancel out the effect of glottis. Then frame-by-frameanalysis was used with hammingwindows and liner predictive coding(LPC) and auto correlation toextract the formant values.
In vowel analysis, frequency values regarding firstformant, and second formant, were extracted and the voweldistribution was obtained by plotting . In the analysis of vowel distribution, primary cardinal vowelsintroduced by Daniel Jones were used as a reference. *Results MATLABis used for scripting, calculations and analysis. In the frame by frame analysis, speech signals are divided into a non-overlapping frameof samples. Figure 2 shows the vowel distribution for the all 15samples.
Percentage distribution is shown in Figure 3, while a further analysisof denser areas is indicated by Figure 4 and Figure 5. Figure 6 offers acomparison of vowel distribution with primary cardinal vowels. DiscussionVoiced to unvoiced ratio calculation, whencombined with zero-crossing rate and energy content, demonstrated of framesas voiced while of framesas unvoiced. Further, it demonstrates a clear tendency to pronounce vowels inchanting Angulimala sutta.A previous research work on formantfrequency tuning in professional Byzantine chanters shows clear evidence thatchanters have special ability to use personal formant tuning at chanting 2. Inthis analysis, vowel distribution shows most common area for all chanters asshows in figure 2. The calculation of the percentage values indicated that of vowels concentratearound the frequency range of and as shown in Figure 3.
Further analysis demonstrated the area bounded by, and represent and of vowel distribution respectively as showingin Table1. ConclusionThe Angulimala sutta is rich with vowels as it shows approximately voiced to unvoiced ratio. Analysis of thesevowels suggest that of vowels concentrate around the frequencyrange of ~ and showing high amount of low back unroundedvowels.
When comparing the results with Cardinal vowel chart, the densest vowel area shows thequalities of cardinal vowel a and ? as shown in Table 2. It can be concludedas when chanting the Angulimala sutta, the arrangement is inclined to bethe tongue is low positioned in back levels while lips shapedunrounded. Less number of vowels are represented by cardinal vowels i and u,showing high front unrounded vowel and high back rounded vowels respectively.
