Miku Append is just re-recordings of Saki Fujita's voice, but with different feeling in the voices.
Miku Sweet- The "Sweet" Append is meant to be a sweetie sounding version of Miku's voice. This vocal is a cute, higher-pitched whisper voice.
Miku Dark- "Dark" sounds আরো mature and broken-hearted. Wat described Miku's "sexy" vocal as being broken up between this voice and "Soft"
Miku Soft- "soft" as a voicebank is optimal for backing vocals and long notes. Wat described Miku's "sexy" vocal as being broken up between this voice and "Dark".
Miku Light- This voicebank is cute sounding and has a sense of happiness to it.
Miku Vivid- "Vivid" is a strong sounding vocal.
Miku Solid- This voicebank sounds strong and powerful.
The appaned version's of ythe ভোকালয়েড have 6 অথবা 7 আরো voice banks (i can't remeber edsactly how many) It's makes their voices much clearer, and people think it also them sound older.