Okay, the first thing is mixed sounds. As you see the above video is Nyan cat. Nyan is one of the words that uses a mixed sound. Without knowing about the double sound you would think that it would be written N-ya-n, as those are the kana that you know.
But Japanese has one set of double sounds. Any kana that ends in -i (apart from the single I kana) can be a double sound with one of the y- sounds.
So, nyan is actually Nya-n.
Let me show you with actual kana.
You can see that the second kana is smaller than the first one. This way you can see that you're talking about a kana that is not used on it's own but in a combination.
The rule of mixed sounds: any kana ending in -i can also be ended in y-.
Here is the list of all the combination kana:
|き||きゃ||きゅ||きょ||ki, kya, kyu, kyo|
|し||しゃ||しゅ||しょ||As with the regular kana shi, this is sha, shu, sho|
|ち||ちゃ||ちゅ||ちょ||again, as with chi, these are cha, chu, cho|
|に||にゃ||にゅ||にょ||ni, nya, nyu, nyo|
|ひ||ひゃ||ひゅ||ひょ||hi, hya, hyu, hyo|
|み||みゃ||みゅ||みょ||mi, mya, myu, myo|
|り||りゃ||りゅ||りょ||ri, rya, ryu, ryu|
The same rules when it comes to dakuten also goes for these double sounds, so きゃ becomes ぎゃ and so on.
Doubling of sounds
In a lot of languages we simply double vowels or consonants when we want a longer sound or something like that.
For consonants Japanese has a special kana for that. It's the small sign of つ.
きて = come
きって= postage stamp
The only time this doesn't work is with the N sound. To double a N you use the ん with one of the kana from the N line.
Pronunciation wise it is a bit different from how we double the consonant. To properly pronounce it in Japanese you don't pronounce it double but you start pronouncing the sound, pause, and then pronounce the rest. Try it, it's a bit different but it is doable.
For vowels it's slightly different. You double the kana of the vowel you want to lengthen. So a long か is かあ and a long に is にい.
Though there are two exceptions. An O sound is usually doubled by a U though in older words it is still an extra O. Like よう vs おとおさん. The other exception is the E, it is usually lengthened with an I and other another E, like せんせい, unless in some older situations. Another exception is when the word is split exactly where the vowels are next to each other in these two cases, then you do read them as o+u and e+i. Though you can hear that, so you don't need to worry about that too much.
Something about ん
Since you can you use the N on it's own and it can be followed by a vowel you need to pay attention to the word. In some cases the split in a word is right after a ん (as you can see above) and the next part of the word can start with a vowel. In this cases you don't use kana from the N row but simply ん + vowel. This is something that you will run into while learning kanji and isn't as confusing as it now looks as it's obvious where the split in a word is with different kanji.
That is it!
Next week I'll be starting the first set of katakana.