The nasal consonants are ㄴ and ㅁ. To keep pronunciation easy and flowing some consonants get changed before these two consonants as shown below:
Some p-based sounds become ‘m’:
ㅂ, ㅍ —> ㅁ sound Some t, s, ch, and h-based sounds become ‘n’:
ㄷ, ㅌ, ㅅ, ㅆ, ㅈ, ㅊ, ㅎ —> ㄴ sound k/g based sounds become ‘ng’, like in English singer (not sin-ger)
ㄱ, ㅋ, ㄲ —> ㅇ sound
ㄹ also has its own assimilation rules. If ㄹ and ㄴ come together, the ㄹ wins (don’t say the ㄴ at all). It means the n BECOMES an l. If ㄹ comes before an ‘ｉ’ or ‘y’ sound the ㄹ sound is doubled. More of an ‘l’ sound than an ‘r’ sound.
ㄹ + ㄴ —> double ㄹ (l) sound
ㄹ + (이, 야, 여, 유, etc.) —> double ㄹ (l) sound
The following shows the difference between untensed and tensed consonants in Korean: Untensed
Sometimes it’s easier to tense a consonant when it’s before another strong consonant, rather than assimilating it like we did with the nasal consonants
ㄴ and ㅁ. Examples
Aspiration and ㅎ weakening
The ‘h’ sound is very weak in English as well as Korean. For example, when you pronounce ‘hour’ it sounds like ‘our’. The ‘ㅎ’ tends to become silent in casual speech between vowels, after the nasal consonants ㄴ and ㅁ, or after the consonant ㄹ.
말해 봐 마래 봐
When ㅎ precedes or follows immediately ㄱ, ㄷ, ㅂ or ㅈ, it becomes silent but making these soft consonants harder (or aspirated): Softer