Band Hero

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; "Pat Benatar - Love Is A Battlefield", I've linked in a video below showing you the song and a full band FC, you don't need to be playing with a full band for this achievement, but the video shows you what to expect for every instrument on it's hardest setting.

* ^{Credit to RevengeOfPazrevenge for the video}

The secret notes for this one are on Pat Benatar's "Love is a Battlefield". 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.

Pat Benatar -- Love is a Battlefield

I am pretty sure that the series of notes that need to be hit 100% are somewhere in one of two places (I know this from missing one note in two different places and did not get the achievement):

Enter the Battle
Battle Cry

*If anyone wants to comment on my solution and tell me where they know the notes are not, I will update this solution until we know which section it is.*

The way i got this achievement was during my beginner vocals career run, i just played through the song Love is a Battlefield by Pat Benatar (check the hint) and it popped up after i beat this song. Not to sure if this concept of playing vocals applies to all Secret Notes because im missing some in my vocals run which ill go back on other instruments