Is '시' pronounced as 'shi' or 'si'?
With 'ㅅ,' I thought it depended on the following character as I've seen it written as 'sh' or 's'
For example,
시간 (time) is pronounced as 'shigan' or 'sigan'? I've literally heard people say 'shi' but Google translate writes it as 'sigan'...
수호 (guardian) is pronounced as 'suho' and I don't expect it to be pronounced as 'shuho'
From Wikipedia:
The sibilant /sʰ/ has behavior of both the plain and aspirated stops: it is aspirated, at least word-initially, and it does not become voiced intervocalically like the plain stops but has relatively brief contact (shorter than /s͈/), like the plain stops. The analysis of /sʰ/ as phonologically plain or aspirated has been a source of controversy in the literature; phonetically, however, it is aspirated. /sʰ, s͈/ are palatalized [ɕʰ, ɕ͈] before /i, j/.
In other words, 시 is [ɕʰi]. The sound [ɕ] does not occur in mainstream English. In other languages, it's same as Mandarin pinyin "x", and Swedish "tj" sound. It's a voiceless alveolo-palatal sibilant fricative, and describing it in terms of English "sh" or [ʃ] is wrong. It's just not the same sound. Different tongue position, different place of articulation.
시 is always pronounced "shi." The issue of "si" versus "shi" is one of romanization. In some romanization systems, ㅅ is always transcribed as "s," regardless of what vowel follows. So "시" would be written as "si" in such a system.
But, the pronunciation of 시 is singularly "shi."
However, syllables such as 수, 사, 소, etc. are pronounced "su," "sa," and "so" respectively.
Of course, '시' is pronounced as '시'. :)
To give a more helpful answer, you are correct in that ㅅ in '시' is similar to English "sh", or more precisely, IPA symbol [ʃ]. (Edit: it's apparently [ɕ], which is a similar(?) but different sound.)
However, note that [ʃ] in English is usually pronounced with rounded lips, so the English word "she", for example, will be perceived more like 쉬 than 시 by a Korean speaker.
As Vladhagen said, the most common Romanization scheme currently in use ("Revised Romanization" as wikipedia calls it) uses 's' for all occurrence of ㅅ, when it starts a syllable. It actually makes sense: you don't want the transliteration of a language to show differences of a sound that a native speaker perceives as the same ("allophones"): it would be like trying to write "pin" and "spin" using two different versions of p's, because only "pin" is aspirated (a distinction which most English speaker is oblivious of, because their brains choose the correct sound automatically).
Another scheme that used to be popular, the McCune–Reischauer (MR), does make the distinction: so 시 will be written as 'shi' using MR.
In terms of pronunciation in Korean or any other languages, I find the Forvo website brilliant. Take a look at forvo.com.
I don't think you can rely on romanization, as there is no official way to romanize Korean (as far as I know?).
