Acoustic Analysis of the Fifth Liquid in M alayalam (2023)

Abstract: This paper investigates the claim of rhoticity of the fifth liquid in Malayalam using various acoustic characteristics. The Malayalam liquid phonemes are analyzed in terms of the smoothness of the pitch window, formants, formant bandwidth, the effect on surrounding vowels, duration, and classification patterns by an unrelated classifier. We report, for the fifth liquid, a slight similarity in terms of pitch smoothness with one of the laterals, similarity with the laterals in terms of F1 for males, and similarity with the laterals and one of the rhotics in terms of F1 for females. The similarity in terms of formant bandwidth between the fifth liquid and the other liquids is inconclusive. Similarly, the effect of the fifth liquid on the surrounding vowels is inconclusive. No similarity is observed between the fifth liquid and the other liquids in phoneme duration. Classification of the fifth liquid section implies higher order signal level similarity with both laterals and rhotics.

## introduction malayalam along with tamil has five liquid phonemes. alveolar lateral /l/, retroflex lateral /í/, alveolar tap /r/, alveolar trill /r/ and a fifth liquid /ü/. there have been attempts to classify the fifth liquid /ü/ in malayalam either to laterals or to rhotics. the fifth liquid in tamil /ü/ is reported to be acoustically more similar to lateral /í/ @xcite . based on the phonetic and phonological characteristics, there were suggestions on the rhoticity of the fifth liquid in malayalam @xcite . phonological characteristics like non-gemination or occurrence at only the inter-vocalic positions point toward the fifth liquid's supposed rhoticity. to analyze the malayalam liquids, other than just using voice signals, other modalities like static mri and ultrasound are used, especially in uncovering the articulatory configurations @xcite . in @xcite , although the authors support the rhoticity of the fifth liquid overall, they report that the position and configuration of articulators vary widely among the rhotics, for the same word for different speakers. in this paper, we seek acoustic-phonetic data patterns for any similarities between the fifth liquid and rhotics/laterals. the rest of the paper is organized as follows. first, the details of the malayalam liquid dataset used for analysis are discussed. next, a pitch smoothness function is introduced and the pitch smoothness of malayalam liquids is measured and compared. then, the formants of the fifth liquid are compared with the laterals and the rhotics genderwise. after that, the claim of low f3 for rhotics compared to that of laterals is assessed. then, the formant bandwidth of liquids is analyzed genderwise. next, the effect of the liquids on the surrounding vowel formants is discussed. after that, liquids are analyzed in terms of their duration. finally, an unrelated english framebased phoneme classifier is used to understand the classification patterns of the fifth liquid section in malayalam. ## analysis every similarity analysis (except for the pitch smoothness and the classifier-based analysis) is formulated as a statistical hypothesis test that compares the relevant acoustic feature from 2 broad phonemic classes. the null hypothesis is that there is no difference between the acoustic feature in consideration between 2 phonemic classes. ## conclusion and future work the claim of rhoticity of the fifth liquid in malayalam is analyzed using various acoustic-phonetic characteristics. first, the details of a small malayalam liquids dataset are described. the average absolute teager-kaiser energy operator is used to measure the smoothness of the pitch window of various malayalam liquids. for the fifth liquid, there is a noticeable difference in terms of pitch smoothness with the rhotics. next, the formants are used to measure the similarity between the fifth liquid and the other liquids, gender-wise. the difference between the formants of the fifth liquid and the other liquids is significant, irrespective of gender. next, the hypothesis that the f3 of rhotics is lower than that of the laterals is tested. for females, there is no evidence for the rhotics f3 being lower compared to laterals f3. then, we analyze the formant bandwidth genderwise. formant bandwidth does not seem to offer any definite evidence to classify the fifth liquid as either laterals or rhotics. after that, the assumption of the fifth liquid affecting the f1 and f2 of the surrounding vowels in specific ways, compared to that of laterals and rhotics is analyzed. no definite evidence could be obtained that supports this assumption. then, the duration of the fifth liquid is analyzed and contrasted with the remaining liquids to find any similarities. no statistically significant similarity is observed for the duration between the fifth liquid and any other liquids. finally, an unrelated classifier is used to classify the fifth liquid section to see the generic frame-level recognition pattern. classification of the fifth liquid section implies higher order signal level similarity with both laterals and rhotics. articulatory configurations, not provably reflecting in signal level data, cannot be the mere deciding factor for broad phoneme classification. more data-driven spectral level features from context dependant realization of the fifth liquid may provide more insights into how similar the fifth liquid is to laterals/rhotics. the recent advances in multilingual acoustic representation learning could provide further insights into the real nature of the fifth liquids @xcite . the various acoustic pieces of evidence considered, in the context of this paper, are not sufficient enough to conclusively classify the fifth liquid in malayalam as rhotic.