Hi and thanks for responding to my BN check request!
I used the above-mentioned Spectro program and the sound quality problem is indeed present upon checking the main audio file. Now the suggested 128kbps mp3 is applied as the main audio.
This suggestion certainly helped me learnt how to check for the sound quality and its audio cut-off (to reduce the beatmap file size while keeping the main audio quality). Thank you so much for taking your time here ^_^
(Listing the changes I made)
7/21/2020
Normal
Hard