A tool that converts wav files to bcwav files for custom sound effects in 3DS themes! (yes i used this aswell.)
Do not open the "ctr_WaveConverter32.exe". It is not supposed to be opened.
How to use: Save the archive to your Downloads folder and extract it to it's own folder. Run Command Prompt and type "cd Downloads" then hit enter. Type "cd ctr_WaveConverter32". Now paste in this command:
ctr_WaveConverter32.exe --pcm16 inputwavfilename.wav -o outputfilename.bcwav
Change the "inputwavfilename" to the name of the wav. Keep the ".wav" or it won't work! (Make sure to put the wav in the ctr_WaveConverter32 folder!) Change the "outputfilename" to whatever you want the name of the output file to be. Keep the ".bcwav" or it won't work! Now hit enter and your bcwav should appear in the ctr_WaveConverter32 folder!
To use the bcwav as a sound effect for your 3DS theme, open 3DS Theme Editor, select your theme, click on Experimental > CWAV Manager. Choose your sound effect, save the theme and you are done! Make sure to enable the "Sound effects" flag or there will be no sound effects.
Download ctr_WaveConverter32 here.
By the way I'm not the creator of ctr_WaveConverter32, Nintendo created this tool, I'm just posting it here because nobody can seem to find it anymore. All credits to Nintendo for this tool.