a range of tube amplifiers and different sized speaker cabinets, all using the same amplifier and speaker. These are known as modeling amplifiers, and can be programmed with simulated characteristic tones of different existing amplifier models (and speaker cabinets—even microphone type or placement), or dialed in to the user's taste. Many amps of this type are also programmable by way of USB connection to a home computer or laptop. Line 6 is generally credited with bringing modeling amplification to the market. Modeling amplifiers and stompbox pedals, rackmount units, and software that models specific amplifiers, speakers cabinets, and microphones can provide a large number of sounds and tones. Players can get a reasonable facsimile of the sound of tube amplifiers, vintage combo amplifiers, and huge 8x10” speaker stacks without bringing all that heavy equipment to the studio or stage. The use of "full range, flat response" (FRFR) amplification systems by electric guitarists has received an extra impetus from modeling amplifiers. Before widespread availability of modeling, guitarists did not commonly plug electric guitars straight into PA systems or powered speakers because most genres relied on the tonal coloration of a regular guitar amplifier setup—from the preamplifier, equalization filters, power amp, guitar speakers, and cabinet design. The FRFR approach assumes the tone is shaped by sound processors in the signal chain before the amplifier and speaker stage, so it strives to not add further coloration or dedicated combo-style amplifiers with a broad frequency range. Such processors can be traditional guitar effects, a modeling amplifier (without power amplifier), or a computer running tone-shaping software. Using a modeling amp or a multi-effects pedal used with line level output, a guitarist can plug in the guitar into a flat response mic input or into a keyboard amplifier. Acoustic Acoustic amplifiers are intended for acoustic guitars and other acoustic instruments, especially for the way these instruments are used in relatively quiet genres such as folk and bluegrass. They are similar to keyboard amplifiers, in that they have a relatively flat frequency response with minimal coloration. To produce this relatively "clean" sound, these amplifiers often have powerful amplifiers (providing up to 800 watts RMS), to provide additional "Headroom" and prevent unwanted distortion. Since an 800 watt amplifier built with standard Class AB technology is heavy, some acoustic amplifier manufacturers use lightweight Class D amplifiers, which are also called "switching amplifiers." Acoustic amplifiers produce an uncolored, "acoustic" sound when