Bits 10 - 7, AUD3 - 0, are assigned to the audio channels. They are called
AUD3, AUD2, AUD1, and AUD0 and are assigned to channels 3, 2, 1, and 0,
respectively.

This  level 4 interrupt  signals "audio block done." when the audio dma is
operating in  automatic mode , this interrupt occurs when the last word in
an audio data stream has been accessed. In  manual mode , it occurs when
the  audio data register  is ready to accept another word of data.

See Chapter 5, "Audio Hardware," for more information about
 interrupt generation and timing .