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In the late 30s a visionary film financer, Ram Daryani, brought a 20 year old Anil Biswas from Kolkata to work for Sagar Movietone Orchestra. Music director Ashok Ghosh gave him freedom to create the first real orchestra for Hindi films. Parallely, Himanshu Rai and Devika Rani, in their newly launched Bombay Talkies, employed the first lady composer, Saraswati Devi.
The first songs which appeared on the big screen in 1935-36 must have been from the movie Achhut Kanya and some other contemporary Sagar Movietone. In the same time frame K. L. Saigal also made his debut as a singer and was a big hit.
To summarize we can say that 1930s was the time when the talkies started as so began Bollywoods life long association with song and dance