Bass amps come with a range of different input and output jacks, depending on the cost of the amplifier and its intended purpose. The least expensive practice amps may only have a single 1/4" input jack and no output jacks. Some practice amps and small combo amps have RCA or 1/8" inputs for plugging an MP3 player or CD player into the bass amp, to facilitate practicing with a recording. Some amps have a high-gain input, for basses which have internal preamplifiers on the instrument. The high-gain input is routed through a pad (attenuator). An amp may also have a low-gain input, which is unattenuated, for regular basses.