This chapter has already mentioned sound briefly, but this section presents more detail, addressing several topics: sound effects, ambient sounds, music, dialog, and voiceover narration.
Keep music, sound effects, and recorded speech in separate files, and play them back through separate channels on the machine. Always include a facility that allows the player to adjust the volume level of the music independently from the volume level of the other audio effects—including turning one or the other off completely. Many players tire of hearing the music but still want to hear the sound effects and other sounds. Bear in mind that not all your players will have perfect hearing, and the more control you can give them, the better. See "Accessibility Issues" in the Appendix, "Designing to Appeal to Particular Groups."