The reason that these are useful is that encompasses all sorts of extra subjects like alternate tuning scales (you may well have those lurking inside your synth but you've never seen the need for them) and microtones. So hopefully some of this info will be useful for soundtrack composers seeking that extra 'ethnic' quality to their sounds.
Now while Western practice divides up the scale into 12 semitones, and also uses equal temperament, so that all keys sound the same in the relationship of one tone to another, the Indian scale is divided up into no fewer than 22 semtones. So you can have notes that are 'out of tune' to Western ears, but are still corect. When Christian missionaries introduced the harmonium to India in the usual misguided attempt to 'convert the natives' it was taken up with enthusiasm and is still used today; however, it's something of an anomaly compared to all other Indian instruments in that it can't get those microtones.
Here's the bit about tuning: all Indian Instruments use Just Intonation, which is derived from the natural harmonic series, so that (for example) thirds, sevenths and ninths actually sound (to our ears) slightly flat. String players can find that out for themselves with the natural harmonics of each string, and brass players can get natural notes by using just lip pressure instead of the valves and pistons on the instrument.
So it's the natural overtones that gives Indian Music it's character, particularly in drones.
Now let's look at scales (he says, finally getting to the point).
Despite the 22 notes in the octave in Indian music, scales are still seven notes, called 'Septak'. The basis of a scale corresponds exactly to the C major scale in Western Music, but the note names are different. Be aware, however, that there's no key changes or modulations, and harmony in the form of chords is virtually unknown. Also a raga can start on any note, dependent on the instrument's range, tuning, or the range of a vocalist. Ravi Shankar tunes his sitars to C#.
For simplicity, we'll use C as the tonic baseline.
Here are the notes of the scale:
C D E F G A B C.
or: Sa Re Ga Ma Pa Dha Ni Sa.
Although there are up to 72 different scales available in Indian Music,
We'll just list the most common ones.
Bilawal (Ionian) : C D E F G A B C.
Khammaj (Mixolydian): C D E F G A Bb C.
Kafi (Dorian): C D Eb F G A B C.
Asavari (Aeolian): C D Eb F G Ab Bb C.
Bhairavi (Phyrgian): C Db Eb F G Ab Bb C.
Bhairav: C Db E F G Ab B C.
Kalyan (Lydian): C D E F# G A B C.
Marwa: C Db E F# G A B C.
Purvi: C Db E F# G Ab B C.
Todi: C Db Eb F# G Ab B C.
In Carnatic music the scales can be much more developed, and here are some basic ground rules for the 12 note scale.
1st and 5th notes (C and G) are regarded as fixed.
The 2nd note can be Db, D or D#.
The 3td note can be Ebb, Eb or E.
The 4th note F or F#.
The 6th note Ab, A or A#.
The 7th note: Bbb, Bb or B.
Any combination of the above can supply the 72 variations of the scale.
Now a scale can be 5, 6 or 7 notes. Some ragas can use different numbers of notes in ascending or descending scales, while there are also strong, weak or neutral notes in each scale, and there are notes of geater or lesser importance in ragas. That's why you can have thousands of ragas for each scale, with new ones beinfg composed all the time! Then add embellishments and note bends (those microtones again) and the sky's the limit!
So hopefully this brief excursion into alternative tunings, scales, modes and ragas might inspire you to try out some of the more unusual ones on your synth.
Remember that the whole subject of unusual modes has been long in use in jazz (Ornette Coleman studied with Ravi Shankar, and Big Band leader Don Ellis had his own Hindustani jazz sextet in the 60s) so there's a whoile new world of stuff to explore.
Just one more word on alternate tunings: check out synth maestrette Wendy Carlos' recordings, particularly Switched on Bach 2000 and Sonic Seasonings to hear how alternate tunings work.
(and now you can go and have a cuppa!)
Lots of Ataris which keep on going, 12 Kurzweil 1000 modules, a bunch of hardware synths. Still recording to tape -the old ways are best.....