Then, download the music that you want to be your sound pack.
After opening Wave Pad Sound Editor, insert the music file into Wave Pad, then start cutting out the parts that you do not want, the remaining parts will be your sound pack.
Like from the starting of the song to 7 seconds of the song, its one part of your sound pack.
After saving the files that you want to be your sound pack, make sure that each part isn't longer than 30 seconds. Then convert the files into .wav if you haven't.
This is a good website to convert your files : Convert audio to WAV
After converting into .wav, you can start renaming the audio files into 1kill, 2kill, 3kill etcetc. Paste them in your Blackshot folder.