The eternal vibration of universe is the force of universe and also the vibration inside our body.
Hence, musical chanting of AUM was actually the invoking of inner chakras and forces through music.
AUM is made by three syllables;
1. Aakaar- means aaaaaaaaaa
2. Ukaar- means uuuuuuuuu
3. Makaar- means mmmmm
All these syllables are derived from ancient chants and mantras and music is the science of sound. Hence, it’s also called swar taantra or swar yoga. Hear them here: https://www.youtube.com/watch?v=yZFG9NPcaGo
Here are the dhrupad ustaads: the Gundecha Brothers:
Based on decades of training and immersion in the science of music, Gundecha Brothers provide detailed guidance on the three vocal characteristics that lead to the right technique of singing Aakaar. A singer who can do this correctly can achieve a strong and resonant voice while keeping it healthy and functional for many decades. Especially check out the section starting at 2:35 https://indianraga.com/lesson/learning-to-sing-aakaar-correctly/
Singing in Aakaar
Right from the outset in Hindustani classical music, one must learn to sing in aakaar - which means to sing using only the vowel sound ā. ("aa" is one of the easiest vowel sounds to make).
Most people are used to singing songs with lyrics, which contain both consonants and vowels. Constants play the role of stabilizing the voice and helping it transition from one note to another, so it is much easier to sing tunefully when you use consonants. Take the consonants out, and suddenly you are left without a crutch, the notes seem to merge into each other and become blurry.
The challenge is to train your voice to sing each note with precision and clarity without the consonants. Serious students must eventually practice singing in all of the pure vowel sounds - a (the schwa sound), ā, i, u, e and o, as well as the nasal consonants n and m, because the voice behaves differently with different vowels.
Some notes are harder to hit with certain vowels.
One of the reasons it is important to learn to sing clearly in aakaar is because when you are singing rapid note patterns at dizzying speeds, a pure vowel sound is all there is time for. You cannot afford the luxury of consonants and lyrics at those speeds.
Another reason is that Hindustani classical music requires the artist to improvise melody, and singing in aakaar allows the artist to focus on and freely explore melody.
Apart from all this, there is the very important fact that melody can be experienced at its purest when no distractions in the form of lyrics are present.
Best Practice Tips:
Tips for practicing Indian Classical Music - Aakar https://www.youtube.com/watch?v=HwO_xI7tRVs
Start singing AAKARS ones you are good with Sargams.
For example if you are able to sing all the shuddh notes in proper Sur on Tanpura, you may start with AAKARS.
The next challenge would be to sing AAKAR in sur. For that, you may sing with Harmonium or sing on Tanpura and record and check for mistakes.
The aakar practice is generally preferred even if you are an experienced singer. Especially when you practice in different speeds and try sustaining on each note. It gives better stamina and strength to voice.
Consciously practice one round of plain notes and one round of gamakas.