Band Hero

The secret notes for this one are on Spice Girls "Wannabe". Hidden within a song is a series of secet notes, When you hit these 100% you will unlock the achievement. There is no way of telling where these notes are so getting 100% will guarentee bagging this achievement. Any even easier way of getting all 19 is to use beginner vocals.

Spice Girls - "Wannabe"

Earning 100% notes hit on this song on any instrument and any difficulty is currently the only proven way to unlock the achievement. The achievement will unlock after the song's completion.

For this achievement you need to hit all the notes during a certain section of the song, it's obtainable on any instrument as each instrument has it's own section of notes for the achievement, you only need to do it on one instrument, the same thing goes for difficulty, each difficulty has it's own section of notes for the achievement and again, you only need to do it once on any difficulty to unlock the achievement.

Now the problem is that the sections are unmarked and no-one really knows for certain what or where the sections are, the best way to go for this is to try and complete the song without missing a single note, that will ensure you get the achievement, so play on a difficulty/instrument combination that you're able to full combo and you'll get the achievement.

Alternatively you could use the beginner vocals/mic fan exploit to get this and all the other achievements that are similar to this one, if you have a microphone/headset and a fan you can just leave the mic leaning against the fan while it's on and the game will register it as sound input and you'll be able full combo every song without actually doing anything.

Lastly, for this specific achievement you need to play; "The Spice Girls - Wannabe", I've linked in a video below showing you the song and an expert/guitar FC, remember though, you don't need to play on this instrument or this difficulty setting.

* ^{Credit to ISiLv3rHawKlv2 for the video}