What values should be put in Delay Time and Decay Factor in Echo in order to get closest to the settings done by professionals in Bollywood songs or others in general?
I don’t think there are settings which will do that. “Effect > Echo” is designed to provide a single slap echo like yelling from a canyon, not theatrical production “deep room” echoes.
Koz
Bollywood is very keen on reverb … https://youtu.be/9oJOzvHyS_k?t=2m1s
There are plenty of free reverb plugins which can be used in Audacity.
e.g “antress modern spacer” plugin can easily produce strong reverb effects , or “Anwida DX lite” reverb plugin.