Music of India 5 Sruti - Pitch

Sruti (Carnatic) Sur (Hindustani)

Sruti or Sur roughly translates to pitch, but where in western music the pitch of a tone for example the  A=440Hz that western orchestras( and most other western musicians) tune to which would translate to the La of the Solfège system with the keynote being C. Indian music does not have this fixed pitch principal. So in western music traditions asking any vocalist to sing Do Re Mi from middle C would produce the notes C D and E with the frequencies 261.626Hz, 293.665Hz and 329.628Hz respectively, whereas in Indian music there is no fixed pitch point, Sa, Ri, Ga as tones depend on the vocal range of the singer. 

Saptak
One of the meanings of Saptak is register or octave ( the other being gamut or series seven notes used).This is the register that the vocalist or instrumentalist is most comfortable at performing in. So one performers Sa could be anything from a few cents to a few tones different to another's. Male singers for example would have a lower Sa to female singers. 

The saptak that a singer is most comfortable with will become their Sa, this could roughly relate to a western singer having a prefered key to sing in. This Saptak will become the middle register of the performance with an octave below and one above,  from low to high this gives us Mandra Saptak,Madhya Saptak and Taar Saptak. 

Once the Sa of a vocalist is found the Tanpura (tambura) will be tuned, on a four string Tanpura this tuning is pa sa' sa' sa which gives you the fifth, octave, octave and tonic of the Saptak( here refering to series of seven notes used). This tuning helps the vocalist stay on pitch.
An example of this tuning can be heard here in the key of G.

Your Tanpura - G Scale - 5 kattai

More recently these are now becoming closer to the fixed pitches of western music. In Hindustani music a vocalists Sa is usually described in relation to the Harmonium keys, with Safed denoting a white key and Kali a black key. In Carnatic these are called Kattai, and half Kattai.
Below these are related to traditional western notes.

Carnatic	Hindustani	Western
Kattai 6	Mandra Safed 6 (Low)	A (Low)
Kattai 6.5	Mandra Kali 5	A#
Kattai 7	Mandra Safed 7	B
Kattai 1	Safed 1	C
Kattai 1.5	Kali 1	C#
Kattai 2	Safed 2	D
Kattai 2.5	Kali 2	D#
Kattai 3	Safed 3	E
Kattai 4	Safed 4	F
Kattai 4.5	Kali 3	F#
Kattai 5	Safed 5	G
Kattai 5.5	Kali 4	G#
Kattai 6	Safed 6	A
Kattai 6.5	Kali 5	A#
Kattai 7 (high)	Safed 7 (High)	B

Reference:
'Your Tanpura - G Scale - 5 kattai' mccbala Uploaded 30 Dec 2011(video)[online]Available at:<https://www.youtube.com/watch?v=fCtMNklEQKM>(accessed 1 November 2013)
Courtney David, 'Overview of Indian Classical Music' chandrakantha 2012 (article) [online] available at:<http://chandrakantha.com/articles/indian_music/> (accessed 1 November 2013)
Uttara 'Introduction to Indian Classical Music' Likhati 2010 (blog) [online]Available at:<http://www.likhati.com/introduction-to-indian-classical-music/> (accessed 1 November 2013)
 Krsna Dhenu, 'KKSongs Music Center' Krsna Kirtana Songs 2012 (website)[online] Avalilable at:<http://kksongs.org/music.html>(accessed 1 November 2013)
Szabi Tóth, 'Indian Classical Music' india.tilos.hu 2011(website)[online]Available at:<http://india.tilos.hu/english_raga.html>(accessed 1 November 2013)