Hello

I am having one doubt,
Since window switching and TNS both are used to remove pre echo effect and TNS is more efficent wav to remove pre echo
then , why AAC is using both?
why not only TNS?

Sumit

TNS isn't simply "more efficient".

Whichever method is the best depends entirely upon the circumstances.

Note that short blocks allow, for example, to very dynamically retransmit side information to improve the coding efficiency.

I suspect that TNS could not remove all the pre echo effects on the Long Block mode. That is why you need the short blocks.