It's a question about a voiced and an unvoiced sound. ㄷ is closer to t sound than d, when it is at the beginning of a word. At the same situation,ㄱ is more closer to k and ㅂto p. So most of Korean has difficulty to discern a voiced sound in English. And Korean learners meet same trouble too when they listen ㄱ/ㅋ,ㄷ/ㅌ,ㅂ,ㅍand ㅈ,ㅊ. Hve you ever seen the English name of 부산? It had been PUSAN. But Now is BUSAN. I give you some explains: An initial consonant is any consonant at the beginning of a word. Initial consonants (especially at the beginning of sentences and phrases) are usually pronounced voiceless. For example the ㅈ in the word 저 ("I") is typically voiceless, especially as first word of a sentence. That makes it sound more like "ch" than "j" to an English speaker. The consonants that follow this rule are ㄱ, ㄷ, ㅈ, and ㅂ. Thus, initial ㄱ sounds more like "k" than "g", initial ㄷ sounds more like "t" than "d", initial ㅈ sounds more like "ch" than "j", and initial ㅂ sounds more like "p" than "b": Examples: 가 ([ka]): initial sound is unvoiced. 다 ([ta]): initial sound is unvoiced. 바 ([pa]): initial sound is unvoiced. 자 ([ʨa], "cha"): initial sound is unvoiced. [edit] Middle ConsonantsConsonants that come in the middle of a sentence can follow some complex sound changes, but the two most important changes are whether the consonant follows another consonant or a vowel. For example, the word 막대기 ("stick") has a middle consonant-consonant sequence (ㄱㄷ) and a vowel-consonant sequence (ㅐㄱ). In many cases, a middle consonant with a preceding consonant becomes slightly more tensified, meaning a "tighter, stronger" pronunciation. So the ㄷ becomes a slightly harder "d" ([d̬]), but the second ㄱ is pronounced "normally" ([g]). The same consonants listed in the section above (ㄱ, ㄷ, ㅈ, and ㅂ) are also mainly the ones that follow this rule. Examples: 막대기 ([mak̚d̬ɛːgi]): Middle consonant ㄷ follows another consonant, so it is more tense. 막대기 ([mak̚d̬ɛːgi]): Middle consonant ㄱ follows another vowel, so it has the standard pronunciation. * a source from: http://en.wikibooks.org/wiki/Korean/Essential_Pronunciation_Rules

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