An audio interface is coupled to received a music signal and a microphone
signal. The music signal and a volume control signal are combined in a
multiplier to produce a volume adjusted music signal. In response to an
input signal from a user, the volume control signal is gradually changed
in predetermined increment levels. Thus, the multiplier gradually changes
the audible volume in these predetermined increment levels. The resulting
music and microphone signal are stored in corresponding partitions of a
single memory, and thereafter provided to a mixing circuit. The mixing
circuit combines signal samples read from the memory to produce four
output signals each containing first and second channel samples. The
resultant 8 channel samples are gated in a formatter with respective
channel mute signals which, when asserted, effectively mute their
corresponding channel sample.