The Singing Machine iSM1030BT Instruction Manual page 19

Operation
Using a Bluetooth Device
11
Press the Auto Voice Control (AVC)
button to turn this option On (AVC
ON will appear in the screen) and the
vocals on a multiplex recording are
muted as soon as the singer begins
singing into the microphone. When
the singer stops singing, the vocals
are automatically unmuted.
IMPORTANT: This feature only works
with multiplex media.
12
Press the BALANCE button, and then
adjust the balance level using the
Skip Forward /Skip Back 
buttons.
On multiplex recordings, use the Skip
Back  button to reduce or eliminate
the lead singer's voice and use the
Skip Forward  button to reduce or
eliminate the music.
IMPORTANT: This feature only works
with multiplex media.
13
SKIP: Advance or go back one track
by pressing the Skip Back /Skip
Forward  buttons.
8