How the tt in written is pronounced?
I heard it like a glotal stop
The pronunciation varies from person to person and from dialect to dialect.
The best way to learn how "written" (or any word for that matter) is pronounced, is to listen for yourself. A lot of dictionaries come with a CD-ROM, which provide ample oppurtunity to listen to both the British and American pronunciation of a particular word.
Add a nasal release to Amigo4's suggestion. That's what you hear in American English.
Well, it is a complex phonological environment.
This is what I wrote on englishforums for a similar question.
In the following cases, the first V is stressed.
1. VtVn, t is nasally released.(cf. button, mutton, glutton, Manhattan, written, beaten, Clayton, etc)
2. VntVn, t is nasally released (cf. Trenton, NJ; Scranton, NJ; Mountain View, CA; sentence, etc). The first V is nasalized. 3. Vrtn, t is nasally released (certain, Morton, hearten, Dumbarton bridge, Wharton school, Barton, etc)
4. Vltn: in some words, t is nasally released; in some others, it is not.
4a. No nasal release, instead there is a schwa between t and n in these words: Hilton, Milton, Dalton, Elton, Shelton, CT, Bolton, Dolton, IL, etc. MW transcribes Dalton with a nasal release, but when you hear the Dalton's sound file there, it is not nasally released. However, LPD transcribes with a nasal release and the sound file matches with it.
4b. Nasal release in these words: Walton (from MW), sultan, etc.
How about words like gluttony? Here, you see sonorant gemination. gluttony = glutton (pattern 1) + nee