An apparatus for precise distance measurement has a multiple frequency generator, a laser transmitter, an optical receiver, a first measuring unit, a second measuring unit and a central processing unit. The output transistors are configured to turn on to change a voltage of the output terminal. The signal processing apparatus estimates a sound source direction using an audio signal processed by the first processing unit or an audio signal processed by the second processing unit. The inner, or delivery, lumen generally may be used with a guidewire to access target sites within the body via the flexible, small diameter vessels of the body.