Do you know how to do the music at some point was muffled, like from behind the wall?
Try Effect > Equalization and make it look like the attached.
or the Low Pass filter: http://manual.audacityteam.org/o/man/low_pass_filter.html
It can be progressively-muffled with this variation of Steve’s code in the Nyquist Prompt …
(setq start-freq 22000) ; cannot be greater than 1/2 the sample rate (setq end-freq 200) (setq passes 6) ; more passes for a steeper filter cut-off (setq sweep-type 0) ; 1 for a linear sweep, 0 for exponential sweep (let* ((nyq (/ *sound-srate* 2.0)) (f0 (max 0 (min nyq start-freq))) (f1 (max 0 (min nyq end-freq)))) (if (= sweep-type 0) (setf lpfreq (pwev f0 1 f1)) (setf lpfreq (pwlv f0 1 f1))) (dotimes (i passes s) (setf s (lp s lpfreq))))
If you reverse the track then apply the code , (then reverse it back) , it gradually becomes less muffled,
similar to … https://soundcloud.com/glitchhop/amb-get-loose#t=2:33