Listen to this Parul Ghosh song (Number 09) 'ummeed unase kyaa thee' from
One can clearly hear her taking a breath in between singing. Same phenomenon can be heard in the early songs of Lata, Noor Jehan and Suraiya, for example. No breathing can be heard in the early 30s songs, try plenty of them on the website. Of course, it disappeared again starting with early fifties. It;s a puzzle!
The answer is that in the very early days, the songs were recorded at the same time as video and the mike was out of the frame, far away, so and breathing was faint like a whisper. When audio and video got separated, the singer could put his/her mouth very near the mike, so breathing is heard. I like the songs with breathing because it makes me feel that the singer is sitting very near me and singing only for me.
So, what happened? Somebody thought that the breathing was a bad thing and taught the singers to move their mouth away from the mike to breath in. I am not sure but usually Anil Biswas is credited/blamed for teaching Lata how to breath like this and everybody followed her.
Now you know!