apk add pulseaudio
Pulseaudio should run with an elevated priority, because e.g. crackling or delayed audio is more annoying than a low framerate in games.
Installing the shadow package (which is compiled against linux-pam) is an easy way for the non-root user to be granted the ability to change niceness, and pulseaudio is recommended to be run as the user, rather than as root. E.g. in /etc/security/limits.d/audio.conf (and putting the user in the "audio" group):
@audio - nice -11