Let's try to understand, with the help of image above, about where the three main octaves of music are located on a harmonium or piano. We will see it for scale A# in this lesson.

If you want to know about saptak or octaves and how do they sound, watch this video lesson, Introduction to octaves/saptak in music.

We discussed in detail about sequence of 12 notes on harmonium/keyboard for scale A# in this lesson, representation of 12 notes for scale A#. See this lesson to understand keys of all swars such as Sa, Re, Ga, Ma on harmonium/piano keys for scale A#.

Now with A#2 as 'Sa', which is also called madhya saptak Sa or middle octave Sa, the Ni (Nishad) of this octave will be A3. This octave and its notes are shown in green colour in the image. Hence the 'Sa' of next octave, called taar saptak 'Sa', is A#3 which is one note higher than A3, Ni of madhya saptak. Similary, for this octave the Ni will be A4. This is shown in light blue colour in the image above. Likewise the Ni of octave lower than middle octave, called mandra saptak, will be A2 which is one note lower than A#2, Sa of madhya saptak. This octaves 'Sa' starts from A#1, shown in purple colour in the above image.

For similar example in scale C#, see this lesson Representation of three main octaves on harmonium | Scale C#.