Bollywood has long been known to take less risks with the frequent changes. Whether it is about introducing science fiction in the movies, or taking technology to a whole new level with the use of VFX for visual effects. And the same happened in the case of stereo systems as well.
It took a lot of time for Bollywood to realize this technology and use them in their songs.
The era of 50s
Earlier, Bollywood songs were very simple. This is the era of 50s which I am talking about. When the songs were made during that time, people used to sit in front of the mikes and started singing and recording the songs. If you watch any youtube video of 50s Bollywood songs, you will find people singing and playing instruments in 1 video only.
That is, a group of people used to sit together. Some used to sing, while some used to play the instruments like Sitar, Harmonium, etc. in the background. All of this used to get recorded by the mike alone, which was kept in front of the singer.
But later the techniques changed.
The era of 80s
Later on, every instrument was recorded separately, and were then overlapped with the lyrics of the song.
This is known as stereophonic sound method, where more than 1 channels of sound are used simultaneously. Although stereo system was invented and introduced in the 30s, but it took way too many years for it to enter Bollywood. It was not before the 80s movies, that movie makers started including stereo system sound method in their movies and songs.
And by this time, the monophonic sound method had eliminated completely. Everything had turned stereo now. But this is when such a system made its mark in Bollywood.