In this section...
The nine notes of the Great Highland Bagpipe are an unruly bunch. They fail to conform to western musical standards, and as a result the pipes are rarely accompanied by other instruments, although it can be and is sometimes done quite successfully.
The Scale is not one of the traditional major scale. That is the typical Doe, Ray, Me, Far, So, La, Tee, Doe sense. Instead, the GHB scale has a flattened seventh, that's the Tee! It's a semi tone lower, i.e. nearer the La. This is known as the Mixolydian Mode in the music world. But further to this the notes don't fall exactly in the Mixolydian Mode, that's just the nearest 'label' that can be used to pigeon hole the pipes. In reality the notes are just somewhere near those used in western music, and this no accident or poor engineering tolerances when manufacturing pipe chanters. No, this is to improve the harmonies that are developed against the drones. Let's also not forget that the Great Highland Bagpipes evolved more than a few years ago, and the pipe makers of yesteryear where not concerned by standard western music. These were solo instruments, and did not need to conform.
The tradition on non-conformity still continues, different pipe and reed makers produce their own sound, and as a result bands have to use chanters from the same maker to ease the job of tuning. Over the years the Great Highland Bagpipe has become significantly sharper, furthermore the relative differences between some of the notes have changed to suite the style of playing from ceol mor to ceol beag, that is; from the traditional 'heavy' Piobaireachd to modern 'light' music.
