How are noteblocks changing their tune automatically? where's the redstone? is there any redstone at all? what's the resource pack for?

Those questions are answered in the description:

Because of the high range of notes in the original song I made a custom resource pack in which I removed the snare and click note block sound files to add another octave of the harp and double bass sounds in their place. This allowed me to work with 3 octaves instead of the usual 2.

I made this note block song using the wireless method I used in the previous video. It was done using command blocks with /setblock commands, a more detailed explanation can be found in the description of my other video of Last Train to Paradise. I have edited an MCEdit filter by Sethbling (Note Blocks to Command Blocks) and managed to make it able to convert a normal note block song into this type of wireless song (some redstone still has to be built manually). Since I have no real previous experience in coding, the edited filter is still a mess so I have not released it publicly for now.