You can choose an alarm sound from the bnClock alarm sounds, or choose audio from your library as a wake up sound. However, bnClock must be in the foreground for audio from your library to be used. Otherwise, the built-in "Beep" sound will be used with the system notification service.
The alarm volume can also be set. bnClock tries to use this as an absolue volume setting. This means that if you have set the alarm volume for bnClock very high and later turn down the volume while using another app, if bnClock is in the foreground, it will play the alarm at the higher volume.
Setting alarm audio and volume, selecting audio