From RWP Wiki
Musical Notes are collectible items in the Banjo-Kazooie series.
They are golden musical notes - specifically, each one is a joined pair of quavers (eighth-notes), except in Banjo-Kazooie: Nuts & Bolts, in which they are semi-quavers (sixteenth-notes).
In the Games
In Banjo-Kazooie, Notes were required to break the Note Doors that Gruntilda had set up in her lair. Uniquely for Banjo-Kazooie, Notes cannot be removed from the levels they are in; that is, as soon as the player leaves the level, the Notes are returned to where they were. The highest number of notes collected in the level before leaving or dying was recorded and taken as the player's number of notes from that level. This system often bred frustration: dying after collecting 95 Notes meant that the player had to collect all 95 Notes again in addition to the remaining 5 Notes if they wanted to make 100. The official in-game explanation for this was that Gruntilda's magic prevented Banjo and Kazooie from taking the Notes out of the worlds.
In Banjo-Tooie, both the purpose and dynamics of the Notes were changed. Note Doors were abolished and a Note fee for learning moves was established. Additionally, Notes were treated just like other collectible items, in that once they had been collected, they stayed collected. This meant that a player could collect 50 Notes from a level, leave, return later and collect the other 50 to reach 100. Finally, the Notes were grouped into Note Nests, each one containing 5 Notes, as well as each level featuring a Treble Clef, worth 20 Notes. This meant that there only needed to be 16 Note Nests and one Treble Clef in a level, compared with 100 individual Notes in Banjo-Kazooie. There are 100 Notes in each of the first eight worlds of the game (Cauldron Keep features no collectibles) and 100 in the Isle o' Hags, equaling 900 Notes total.
Banjo-Kazooie: Nuts & Bolts
In Banjo-Kazooie: Nuts & Bolts, Notes come in three varieties, denoted by color: copper (worth 1), silver (worth 5) and gold (worth 10). The Notes differ from their usual appearance in this game: they now appear as a joined pair of semiquavers (sixteenth-notes).
There are 200 collectible Notes in each world, as well as 900 in Showdown Town. Collecting all of the Notes in Showdown Town earns the player an Xbox Live Achievement. There are 1,900 total collectible Notes (the only ones which add to the Totals menu), however, extra Notes can be won in Challenges, from Klungo's Arcade, from Jinjo-freeing, Minjo-capturing, and Jinjo Bingo. The full amount of Notes, collectible and extra, adds up to 5,230. 120 more Notes can be earned in the L.O.G.'s Lost Challenges downloadable content, from completing the challenges therein, thus bringing the full total up to 5,350.
In this game, Notes are used as currency. They can be used to buy vehicle parts and blueprints from Humba Wumba, or to bribe Pikelet in order to keep the corrupt police off Banjo's back. However, it should be observed that buying every vehicle part and blueprint in the game will leave players with 9 Notes left. Bribing Pikelet more than once before buying everything will leave players with insufficient funds. However, since completing the L.O.G.'s Lost Challenges downloadable content earns the player 120 more Notes, this problem can be alleviated.
Banjo-Kazooie: Grunty's Revenge
Banjo-Kazooie: Grunty's Revenge's Note system was largely unchanged from Banjo-Tooie; the only difference was that some Notes were individual, while some were grouped in nests.