It's now much easier to gain access to homebrew because it works on the most up-to-date 3DS firmware. I'll include a video showing how it works and there are instructions for getting homebrew in the description, but I'll also put them here
https://www.youtube.com/watch?v=UNw8tbTbDpw Instructions
To get soundhax for Europeans (& non-Europeans, but this is the only step for Europeans) download this:
http://www.mediafire.com/file/i6acd5plpvl57c5/Soundhax+11.2.rarThen open it. You might need to download WinRAR to open it!
Open the "o3ds" folder if you'll be using an Old 3ds and open the "n3ds" folder if you'll be using a New 3ds.
Put the contents of the folder which applies to your 3DS model on the root of your SD card. Non-Europeans will have an extra step which is in the paragraph below. Put the SD in the 3DS and launch the "Nintendo 3DS Sound" app.
Play the sound I did in this video.
It should take you to the homebrew menu. It might take a few tries because it isn't perfect. If it works, you have Soundhax!
For the final step of getting Soundhax for non-Europeans visit this:
http://soundhax.com/ delete the eur file from the root of the SD card; it should look like this
http://prntscr.com/dsqmxt Then replace it with the file you downloaded after visiting the site at the start of this paragraph :p You should now be able to use Soundhax!
To get the svdt app for homebrew, visit this page:
https://github.com/meladroit/svdt Put svdt.3dsx, svdt.smdh, and svdt.xml in sd:/3ds/svdt/ These can be downloaded from the link above. Now you should be able to access svdt from the homebrew menu.