Shruti is the 'pitch'. Shruti is the 'Aadhaar Shadja' - the fundamental note chosen for the exposition of a raga or a tune.
Choose your Shadja and then be faithful to it throughout your exposition of the chosen raga. The quality of your music is (would be) judged primarily by the degree of fidelity to the 'Shadja' i.e. the Shruti.
Shruti is the mother of all other swaras (Tones, semi-tones, quartertones and microtones). All other swaras proceed from Shadja and ultimately converge into (become one with) 'Shadja'.
After playing (with) all other swaras one comes back to 'Shadja' or 'Sa', to be brief - like a child coming back to its mother's lap after playing with toys for a while. 'Sa' is the starting point and also the final resting place. It is the central point of all music as well.
'Sa' is everything in music. It pervades all music. Music is verily the space between 'Sa' and 'Sa'. Etymologically the word 'Shadja' means that which gives birth to six (swaras). 'Shadja' is none other than the primordial and sacred note 'OM' - the PranavaNada itself.
For a performing musician 'Sa' is always the guiding principle. 'Sa' is to a musician what a compass is for a navigator. A musician would and should stress the Shadja in his performance coming to it as frequently as possible.
The values of all other swaras are determined only in relation to Shadja. That is to say the value of each note is determined by its distance from 'Sa'.
Now, where exactly is this Shadja? It is there everywhere. You can place your fingers on any 'fret' of sitar or any 'key of a piano and say 'this is Sa' That particular sound which emanates from the chosen 'fret' or 'key' becomes your 'Aadhar Shadja' the take off point for all the music that follows.
Unlike in western classical music, the swaras in Indian music are not fixed. Only their values in relation to the chosen 'Shadja' are fixed. The ratios are to be adhered to very strictly. Otherwise you would be producing cacophony instead of music.
The 'Sa' has an intoxicating effect on the listener's mind. The 'Jhala' part of sitar playing is nothing but a rapid and intermittent chanting of 'Sa'. It is the thrilling and mesmerizing climax to the music that preceded.
An elongated 'Sa' leads the listener into a meditative trance. It is verily a sacred Mantra. It is the 'NadaBrahmam', the source of Divine bliss.