The Singing Machine SML645BT Instruction Manual page 19

Operation
Using the LINE IN Jack (Continued)
V
W
U y
— E18 —
5
Adjust the MIC VOLUME control
as desired. Increasing this control
will increase the volume of both
microphones.
6
Rotate the ECHO control to add an echo
effect to your voice. Rotate towards MAX
to increase the echo effect.
7
Adjust the balance between the
speakers using the BALANCE control.
8
Press the power ON/OFF button to
turn the unit off.