Hey! am confused,
can I have 2 different niches on a single domain? or creating a subdomain for it a good idea?
I have a Music download website, now I wanna add news, headline to it, should I consider that on a subdomain or subdirectory, or I can just be publishing on the root domain?
For two niche, use two unique domains. Simple.
But it will be a separate task to main authority and others on a different domain.
My suggestion is
@Julius_Bajaj If your domain sounds like multipurpose, the subdomain is a good idea.
Example:
NDTV.com (Domain doesn’t mean anything so can be used for multipurpose)
Food.ndtv.com For cooking
gadgets.ndtv.com For gadgets and tech
I think applying a SEO tactics of high authority site at brand new domain / low-authority is simply not going to work. If you understand this earliest, it’s better. 
Yes, that’s somewhat I appreciate. But this works perfect if the domains sounds multipurpose as the example given above.
According to Googlers and SEOs, subdomain niche should not be completely different. The niche should be same, topics can be different. This is because subdomain is a part of the main domain. Both are technically same.
When the site authority is high, Google will not see anything else to rank an article/post.
You just can’t give example of NDTV. They’re on a different league.
Okay, It is just a big example so that you can relate.
I have also multiple niche on sub domains, working fine.
Once about dot com was also big site, now over multiple unique domains.