Previous studies have reported several aspects of voicing of the stops spoken by both Korean speakers and Native English speakers (, , , and others). Prevoiced, also known as truly voiced stops, is the production of vibration of the vocal cords starting before the release burst. The value of prevoicing is measured in negative values; prevoicing is also known as negative VOT or lead-voicing . Voicing occurring before the release burst at the onset position of a word as a prevoicing and at the final position of a word has been a subject of various studies across different languages including English and Korean. Even within one language, voicing of the voiced stops can display different characteristics according to different regions of the speakers of the same language . Moreover, in regards to the voicing of English stop voicing, comparative studies have been conducted between Native speakers of English and speakers of other languages including Cantonese, Japanese, Korean, Mandarin, Saraiki, Spanish and Taiwanese (, , , , [6 ]). ·
However, most of these studies were based on Native English speakers’ impressionistic judgements, and little of the studies have been based on L2 English. As for Native speakers of English, regional and gender differences were found in the voicing of the voiced stops. Previous studies conducted by Lisker and Abramson (1964) have shown that speakers do not arbitrarily choose the production of the prevoicing of the voiced stops produced by Native American English speakers; rather, they have a preference for one form or the other . On the other hand, Smith (1978) found that only 52% of sample of 1200 initial voiced stops were produced with a prevoicing [8 ]. Smith noted that occurrences of prevoicing in American English were highest for labial stops; 56% of labials are prevoiced. 50% of the dental stops and 39% of the velar stops were prevoiced. The mean durations (as in time) were, for labials, 74ms, and for dentals, 71ms, and for velars, 65. However, these values reported by Smith were not corresponding with the research conducted later on. Such difference in data could be due to the individual variation . On the other hand, for British English stops, Docherty (1992) noted that there is a gap in the middle of the distribution between 3 ms and -52ms . Previous studies have shown that there are regional differences of the prevoicing of voiced stops of American English . It was also suggested that southern varieties of American English voiced stops are more heavily prevoiced than other varieties of American English . While some studies have reported that no gender related differences were found, others have reported that male speakers’ production have more heavily voiced stops than that of female speakers [1 0 ]. English stop plosives produced by Native speakers of Korean have different characteristics. Major and Faudree (1996) reported that Korean speakers had the greatest difficulty pronouncing voiced stop plosives at coda position of a word. Korean learners of L2 English tend to devoice the stop plosives at the syllabic-final position .
Similar results were shown in the case of syllabic-initial voiced stops for Native Korean speakers. Kim (2011) reported that because of the L1 influence on L2 speech, Korean L2 learners produced the voiced stops as voiceless stops without any prevoicing in utterance-initial position . The current study is designed to observe the occurrence of the voicing of the English voiced stops produced by both Korean and Native English speakers, and then to compare those aspects in regards to the place of articulation (bilabial, alveolar, and velar) and the syllabic position of a mono-syllabic word (onset and coda). Acoustic analyses of the voicing of the English stops are expected to show the longer duration of prevoicing in the productions of the Native speakers as the previous studies. Korean-Spoken English Corpus (K-SEC) was used for this particular study .