Bass effects are electronic effects units that are designed for use with an electric bass and a bass amplifier, or for an upright bass and a bass amp or PA system. Bass effects are commonly available in stompbox-style pedals, which are metal or plastic boxes with a foot-operated pedal switch or button which turns the effect on and off. Most pedals also have knobs to control the tone, volume and effect level. Some bass effects are available in 19" rackmount units, which can be mounted in a road case. As well, some bass amplifiers have built-in effects, such as overdrive or chorus.
Fuzz bass, also called "bass overdrive" or "bass distortion", is an effect which produces a buzzy, distorted, overdriven sound, which the name implies in an onomatopoetic fashion. Overdriving a bass signal significantly changes the timbre, adds overtones (harmonics), increases the sustain, and, if the gain is turned up high enough, creates a "breaking up" sound characterized by a growling, buzzy tone. By the mid- to late-1960s, a number of bands began to list "fuzz bass" in addition to "electric bass" on their album credits. Two well-known examples are the Beatles' 1965 song "Think for Yourself" (from Rubber Soul) and the 1966 Rolling Stones song "Under My Thumb". Album or performance credits for fuzz bass can be found from every decade since then (see examples below).
Fuzz bass can be produced by overloading a bass amp's tube or transistor preamplifier, by using a bass fuzz or bass overdrive effect pedal, or for the most powerful effect, by combining both approaches. In the 1960s and early 1970s fuzz bass was associated with psychedelic music (e.g., Edgar Broughton Band), progressive rock (e.g., Genesis), and psychedelic soul/funk (e.g., Sly and the Family Stone) styles, and it tended to be a "warmer", "smoother", and "softer" overdrive-type sound caused by soft, symmetrical clipping of the audio signal which "round[ed] off the signal peaks rather than razor-slicing" them and filtered out the harsher high harmonics.
In the 1980s and 1990s, overdriven bass tended to be associated with hardcore punk (e.g., Stormtroopers of Death), death metal (e.g., Mortician), grindcore (e.g., Napalm Death) and Industrial bands (e.g., Ministry), and the tone tended to be heavier, more metallic and more grinding. This is achieved by hard clipping of the bass signal, which leaves in "harsher high harmonics that can result in sounds that are heard as jagged and spikey." In the 1990s and 2000s, fuzz bass was also used by indie and alternative rock bands, with a notable example being Muse.
Since the late 1980s, manufacturers have been producing bass overdrive pedals specifically designed for the electric bass, and in many cases they found a way to keep the low fundamental pitch in along with the buzzy overdrive tone. One early model was the Ibanez "Bass Stack" bass overdrive pedal, which was sold in the late 1980s. The simplest fuzz bass pedals have knobs for controlling the volume level, the tone, and the fuzz or overdrive effect. More complex pedals have different distortion effects (e.g., overdrive and fuzz), gates to trigger the volume at which sounds will get overdriven, mixers to mix the natural and fuzzed sound in the player's desired proportions, and multiple band equalizers. Boutique fuzz bass pedals even have unusual effects such as a "starve" effect, which mimics the distortion sound a pedal gives with a dying battery, a diode selector (either silicon or germanium) for selecting the transistor overdrive tone, and an octave selector (above or below the pitch being played).
A bass chorus is an electronic effect used with the electric bass. It creates the same "shimmering" sound as a chorus effect for electric guitar chorus pedals. The difference is that bass chorus pedals are modified in various ways to suit the low pitch register of the electric bass. While several bass chorus pedal manufacturers have modified the chorus circuit so that it does not affect the lower register, others have designed the effect so that it can have an effect on even very low pitches.
The requirements for a chorus effect using a pedal or effect unit can vary depending on the type of instrument being used. Bass is a perfect example because it operates at a lower frequency range than a guitar. As such, a standard multi-level chorus can make the sound of the bass notes much thinner. This problem can be corrected by either mixing more of the un-affected signal into the mix or by increasing the amount of bass frequency chorused in the sound. Pedals such as the "I90" chorus from bass amplifier manufacturer Eden Electronics allow the musician to control both of these elements.
Upright bassists in jazz, folk, blues and similar genres typically use a piezoelectric pickup, which is mounted on the wooden bridge or between the bridge and the body. The pickup is then plugged into a bass amp or the PA system. Before the signal is plugged into a bass amp or PA system, many players use a bass preamplifier, a small electronic device that matches the impedance between the pickup and the amp or PA system. Bass preamps also allow for the gain of the signal to be boosted or cut. Some models also offer equalization controls, a compressor, and a DI box connection, which allows the signal to be plugged directly into a PA system or mixing board with an XLR cable.