ACOUSTIC CUES TO MANNER OF ARTICULATION OF OBSTRUENTS IN MARATHI
Vaishali Patil, Preeti Rao · 2008
Acoustic cues are investigated for manner classification of unvoiced obstruents in Marathi. A statistical analysis of three temporal parameters extracted from the signal in the vicinity of the noise burst indicates the potential of such features in the three-way classification of unvoiced obstruents into fricative, stop and affricate manners. While unaspirated obstruents are accurately identified, the temporal features are ineffective in separating aspirated stops from affricates. Knowledge-based approaches to speech recognition use explicit knowledge about speech in the recognition process. This can be justified to be efficient, with the emphasis on processing speech rather than signals in general. Research on discovering acoustic attributes of linguistic features forms the backbone of knowledge-based systems. Given this perspective, Indian languages have not been studied well enough. The present investigation focuses on exploring acoustic-phonetic features to distinguish obstruent consonants of Marathi on the basis of manner of articulation. Obstruents are typically classified into the manner classes, affricate, stop and fricative. Stops are characterized by a complete closure located in the vocal tract, followed by an abrupt release. Fricatives are articulated by a narrow constriction in the vocal tract, giving rise to a steady frication noise. Affricates lie between stops and fricatives in acoustic properties. While they are produced by complete constriction, the release is accompanied by a distinct frication noise. A number of studies have investigated temporal properties extracted from the speech signal in the vicinity of the release/frication burst for cues to the three manner classes (1,2,3,4). In an early study, Gerstman (5) used subjective perception tests on manipulated speech signals to demonstrate the importance of frication duration in identifying stops, affricates and fricatives. Howell and Rosen (2) measured distinct differences in rise time of the frication between the voiceless affricate ('t�') and fricative ('�') in British English. A cross language study of Mandarin, Czech and German was carried out by Shinn (6) on the stop-affricate-fricative distinction from temporal measurements of rise time, rate of rise and frication duration. Rise time and frication duration were found to provide relatively effective cues to manner. Kluender and Walsh (7) found that rise time was not an adequate cue in a perception test involving voiceless affricates and fricatives. More recently, Hoelterhoff and Reed (4) showed that total consonant duration was very effective in distinguishing stops from affricates and fricatives in word medial and final positions in German. In the present work, we investigate the effectiveness of the acoustic parameters of frication duration, rise time and rate of rise in the identification of manner of articulation of Marathi unvoiced obstruents. Marathi (unlike English, but similar to several other Indian languages) is characterized by the presence of both unaspirated and aspirated unvoiced stops and affricates. Further, the stops and affricates are traditionally categorised by place of articulation rather than manner even though the places of articulation are in close proximity in some cases.