fxdung said:
I am self learning English from audio file, so I don't recognize which part of country!But I am learned that consonant and vowel in English affect each other. So I ask for example for the word "need" while the tip of tongue contact alveolar ridge for "n" other part of tongue prepare for "ee"?It is need not wait until the tip of tongue leave the roof of mouth then pronounce "ee"?Even the tip of tongue does not move at all in pronouncing the word "need"?My goal is listen fast English.
I just tried pronouncing "need".
To answer your question about the tongue position,
- I found that with the tip on the alveolar ridge much (most?) of of the air flow is out of the nose. This gives a nasal sound to the"n".
- Continuing from "n" to "ee", the tip comes down while the back part of the tongue rises to contact near the throat.
The above changes happen smoothly at the same time, blending together.
The changing tongue position also changes the resonant frequency of the vocal tract so that the "n" sound is a slightly higher frequency (pitch) than the "ee" frequency.
The different air flow paths were found by holding a wet hand close to my face while slowly saying "need." (Wet hand was made by using tongue.

)
You also asked about "it" and "need." The "i" sound is very close the the "ee" sound. For the "i", a part of the tongue that is further back is raised in the beginning part of the throat, giving the "i" a slightly higher frequency than the "ee."
The three vowels "e", "a", "i" are different by what part of the back of the tongue is against the top of the mouth/throat. "e" has the most forward position. "a" is a bit further back,' and "i" is at the beginning of the throat.
The "a" is a little tricky with two pronunciations.
- One is when naming the letter as in the above paragraph.
- The second sounds more like "uh", it is less formal, and is very often used in speech because it is easier to say. The tongue position is part way between the "a" and the "i" positions and has a somewhat sudden start (close to a plosive start to be technical).
I do not think I can describe the difference very well, you will have to here it from an Americanized English speaker that is talking casually, and perhaps rapidly.
Congratulations on your good grasp of the language and your well stated questions.
This post became technical, sorry. At least it will give you exercise in translating!
Cheers,
Tom
What is your native language?