I am learning from TTMINK. I'm in the first workbook level but they continued using the ending “-네요”, so I went to Lv3 Lesson 25 to find out what it means. In one of their examples they use 맞다, and I am wondering - Why is there no 't' sound in 맞네요, and there is in 맞다?
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This has to do with batchim (받침) rules! As you might already know whenever ㅈ is in the batchim position (bottom position in a block), as it is in both 맞다 and 맞네요, it's sound changes to ㄷ for ease of pronunciation. Thus, you would expect the pronunciations to be 맏다 and 맏네요 (keep in mind that the letters do not ACTUALLY change, just the sounds). The reason that you have 맞네요 not making a 'ㄷ' sound is because of ANOTHER batchim rule that comes into place. Whenever ㄷ is followed by ㄴ the 'ㄷ' sound changes to 'ㄴ', this is done to make the pronunciation less "nasally". This leaves your final pronunciation sounding like "만네요". For more help you should look up all of the batchim rules on google (don't worry there aren't too many). That should help a lot!
Here is a bit more technical approach.
Let's see 맞다 first. There is a grammatical rule called '음절의 끝소리 규칙', meaning 'Ending sound of a syllable rule'. Basically the rule says that every single consonant in the end of a single syllable, such as ㅌ in 밭, should be pronounced as one of these: "ㄱ, ㄴ, ㄷ, ㄹ, ㅁ, ㅂ, ㅇ". In case of 맞다, the syllable 맞 ends with ㅈ, and when ㅈ becomes the ending sound it sounds exactly like ㄷ. So after the first application of grammar 맞다 sounds like 맏다. And then, there is a rule called '된소리되기', meaning 'Becoming 된소리(don't know how to translate this into English)'. 된소리되기 gives us an order that when there are two given consonants: ㄱ, ㄷ, ㅂ, ㅅ, ㅈ in a row, the latter one should be pronounced as 된소리. So the final output(the exact pronunciation) of 맞다 is [맏따].
And there is another word, 맞네요. First procedure is the same: ㅈ becomes ㄷ based on the 음절의 끝소리 규칙. Then ㄷ meets ㄴ - the first sound of '네'. In this case, an another rule called '비음화': if we apply this into the word, ㄷ becomes ㄴ due to the existence of the ㄴ. So in this case the final output is [만네요].
Maybe you can get some detailed information related to those three rules in English, but unfortunately I can't get one for now.
Here's a summary I created awhile back, with some (perhaps overly verbose and subjective...lol) commentary on the subject as well:
https://plus.google.com/111681410172584068167/posts/bpPqmGdtTXu
It's worth printing out as a reference, I think.
Here's the relevant part to your question:
ㄷ-sound^ before ㅁ/ㄴ
pronounced ㄴ. 닫는 is “단는", 빛는 is “빈는", 바닷물 is “바단물"
[^ recall that ㄷ, ㅌ, ㅅ, ㅆ, ㅈ, ㅊ, ㅎ all sound like ㄷ (‘t’) at the end of a single syllable.]
Story short, the letter "ㄷ" is what creates the "t" sound.
In your example 맞네요 you read it ma-nae-yo, ㅈ is a silent letter here.
