Roland / Boss has finally come out with a really heavy duty pedal, for people who don't like the plastic pedals normally available. This pedal is really cool because it works as a normal volume pedal OR an expression pedal, by plugging into different jacks. For expression use, you don't have to use a Y or Insert cable like with most volume pedals, just a normal cable with stereo ends. They also have an adjustment screw on the bottom for more or less force to move it. The 500H is high impedance for mono guitar or expression pedal control using a high resistance pot. The 500L is stereo and works with low impedance signals for keyboards or active electronics or expression control with a low resistance pot.