Preamplification and effects The basic sound of the amplified electric bass or double bass can be modified by electronic bass effects. Since the bass typically plays an accompaniment, beat keeping role as a rhythm section instrument in many styles of music, preamplifiers ("preamps"), compression, limiters, and equalization (modifying the bass and treble frequencies) are the most widely used effect units for bass. The types of pedals commonly used for electric guitar (distortion, phaser, flanger, etc.) are less commonly used for bass, at least in bands or styles where the bassist mainly plays a rhythm section role. In styles of music where the bass is also used as a soloing instrument (certain genres of heavy metal, progressive rock and jazz fusion), bassists may use a wider range of effects units. Jazz fusion bassists who play fretless bass may use chorus effect and reverb for their solos. A range of other effects are used in various genres. "Wah-wah" and "synth" bass effects are associated with funk music. As well, since the 1960s and 1970s, bands have experimented with "fuzz bass" where the bass is distorted either by overdriving the amp or by using a distortion unit. Fuzz bass was used by psychedelic rock bands in the 1960s and early 1970s and in traditional heavy metal bands (Led Zeppelin) during the same era. Octave-generating effects, which generate an octave below the pitch being played are also used by bass players. Many bassists in modern-day hard rock and heavy metal bands use overdrive pedals specifically made for bass guitar. Since the late 1980s, bass-specific overdrive pedals have been available; these pedals maintain the low fundamental pitch. Using a regular guitar distortion pedal for bass would result in the lower frequencies being greatly lessened. Well-known overdrive effects for bass include the BOSS ODB-3 Bass Overdrive, Electro-Harmonix Bass Blogger, Tech21 Sansamp Bass Driver, the DigiTech XBD Bass Driver, and the Electro-Harmonix Big Muff. Overdrive built into amplifiers Some bass amplifiers have an "overdrive" or distortion effect built into the unit. The Peavey Century 200 has an onboard "distortion" effect on the second channel. The Peavey VB-2 also has built-in overdrive. Aguilar Amplification's AG 500 bass head is a two-channel amplifier, one of which offers a "saturation" control for overdrive. A variety of BOSS combo amplifiers have a built-in "drive" effect. Gallien-Krueger's bass amp heads have a "boost" control which provides a simulated tube overdrive effect. The