guitar's volume control also changes the pickup's equalization or frequency response, which can provide pre-distortion equalization. The simplest guitar amplifiers, such as some vintage amps and modern practice amps, have only a single volume control. Most have two volume controls: a first volume control called "preamplifier" or "gain" and a master volume control. The preamp or gain control works differently on different guitar amp designs. On an amp designed for acoustic guitar, turning up the preamp knob pre-amplifies the signal—but even at its maximum setting, the preamp control is unlikely to produce much overdrive. However, with amps designed for electric guitarists playing blues, hard rock and heavy metal music, turning up the preamp or gain knob usually produces overdrive distortion. Some electric guitar amps have three controls in the volume section: pre-amplifier, distortion, and master control. Turning up the preamp and distortion knobs in varying combinations can create a range of overdrive tones, from a gentle, warm growling overdrive suitable for a traditional blues show or a rockabilly band to the extreme distortion used in hardcore punk and death metal. On some electric guitar amps, the "gain" knob is equivalent to the distortion control on a distortion pedal and similarly may have a side-effect of changing the proportion of bass and treble sent to the next stage. A simple, inexpensive amplifier may have only two tone controls, a passive bass and treble control. In some better quality amps, one or more midrange controls are provided. On the most expensive amps, there may be shelving equalizers for bass and treble, several mid-range controls (e.g., low mid, mid, and high mid), and a graphic equalizer or parametric equalizer. The amplifier's master volume control restricts the amount of signal permitted through to the driver stage and the power amplifier. When using a power attenuator with a tube amplifier, the master volume no longer acts as the master volume control. Instead, the power attenuator's attenuation control controls the power delivered to the speaker, and the amplifier's master volume control determines the amount of power-tube distortion. Power-supply based power reduction is controlled by a knob on the tube power amp, variously labeled "wattage", "power", "scale", "power scale", or "power dampening". In popular culture Volume control gradations are typically numbered from zero to ten. In the 1984 film This Is Spinal Tap, guitarist Nigel Tufnel demonstrates an amplifier whose volume knobs are marked from zero to