“THOUGH M.S. Subbulakshmi assimilated her vast repertoire from many sources, she always acknowledged the late Semmangudi Srinivasa Iyer as her guru. He infused depth and grandeur to Subbulakshmi’s music, strengthened her alapana, niraval, and swara, and taught her majestic compositions.”

Link to the entire article is below : 

A Guru on His Sishya – Article by Gowri Ramnarayan in the Hindu 

An excerpt from MS & Radha – Saga of Steadfast Devotion by  Gowri Ramnarayan

“He (Semmangudi Srinivasa Iyer) noted several special qualities about her voice. It was not just pleasing and pitch perfect but had a  reenkaram (reverberation), sounding the same up close and at a distance;  it was not distorted or weakened when you heard it from different directions.  It had gatram (weight), and remarkable continuity, ” When you strike a temple bell, the echo continues after the sound ends, until the next striking.  Her voice has that quality.  when she stops singing, the naadam (sound) continues”