This is the sound which will be played if the sound specified in the alarm action can't be found. If this sound doesn't exist either, the windows default sound will be used.
Override sound volume
If you check the box, the system volume will temporarily be set to the specified volume when the sound plays. Currently, this will only affect the 'WaveOut' volume.
Here you can select the voice which speaks the alarm message.
Override voice volume
If you check the box, the voice volume will be set to the specified volume when the voice speaks.
Override voice speed
If you check the box, the voice speed will be set to the specified speed when the voice speaks.