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Auto-wah (also known as a "Q-wah", "T-wah", "envelope following filter", "envelope follower" or "envelope filter") is a type of wah-wah effects pedal typically used with electric guitar, bass guitar, clavinet, and electric piano etc. The distinctive choppy rhythm guitar sound on many funk and disco recordings from the 1970s popularized the effect.
Instead of the effect being controlled by a pedal, as on a standard wah-wah, the effect alters in response to the volume of the input signal. [1] Like a wah, it works by adjusting the central frequency of a peaking filter, which amplifies a specific frequency and cuts off other selected frequencies. [2] [3] Since the electronic circuits in the effect can respond much faster than a human musician can physically move a pedal, certain effects that a standard wah cannot achieve are only possible with auto-wah. The response of the effect is highly interactive with the dynamics of the input signal - this makes it possible to vary the response at will via slight adjustments to playing technique. Therefore, it may take some practice before the response of the auto-wah can be wilfully controlled in order to achieve a consistent sound.
A typical auto-wah circuit uses an envelope detector to produce a voltage representing the overall volume of the input. This signal is then used to sweep the cutoff frequency of a filter. The filter usually has a low-pass or bandpass response. The Boss AW-3 is an example of such a device.
There is a variant of auto-wah that utilizes a low-frequency oscillator (LFO) instead of an envelope detector to alter the effect. The filter response varies constantly with time and is not linked to playing dynamics. The Boss AW-2 is an example of such a device. The difference in sound is subtle, but careful listeners will notice the constant period of the filter sweep. The song "Falling Into Grace" by the Red Hot Chili Peppers is an example of an LFO controlled auto-wah applied to the bass guitar.
Typical controls on an auto-wah include a sensitivity control to adjust the input level to match the level expected by the envelope follower and other circuitry, a control for the initial cutoff point of the filter, and a control for the depth of the filter sweep. Some more sophisticated units offer controls for the resonance of the filter, multiple filter types, and options for sweeping the filter up or down.
The first envelope-controlled filter built for musical instruments was the Mu-Tron III, invented by Mike Beigel. [2] Other examples include the MXR Envelope Filter and the Boss AW-2 Auto Wah (LFO controlled).
Grateful Dead guitarist Jerry Garcia is known for extensive use of an envelope filter (particularly the Mu-Tron III), examples being his playing on "Estimated Prophet" and "Shakedown Street". Phish guitarist Trey Anastasio also frequently uses the effect, especially in addition to the use of distortion. The guitar solo in "What I Am" by Edie Brickell & New Bohemians features an auto-wah effect. J Mascis became well known for the use of the effect thanks to his role as guitarist in the group Dinosaur Jr.
An effects unit or effects pedal is an electronic device that alters the sound of a musical instrument or other audio source through audio signal processing.
Subtractive synthesis is a method of sound synthesis in which partials of an audio signal are attenuated by a filter to alter the timbre of the sound. While subtractive synthesis can be applied to any source audio signal, the sound most commonly associated with the technique is that of analog synthesizers of the 1960s and 1970s, in which the harmonics of simple waveforms such as sawtooth, pulse or square waves are attenuated with a voltage-controlled resonant low-pass filter. Many digital, virtual analog and software synthesizers use subtractive synthesis, sometimes in conjunction with other methods of sound synthesis.
Wah-wah is an imitative word for the sound of altering the resonance of musical notes to extend expressiveness, sounding much like a human voice saying the syllable wah. The wah-wah effect is a spectral glide, a "modification of the vowel quality of a tone".
A wah-wah pedal, or simply wah pedal, is a type of electric guitar effects pedal that alters the tone and frequencies of the guitar signal to create a distinctive sound, mimicking the human voice saying the onomatopoeic name "wah-wah". The pedal sweeps the peak response of a frequency filter up and down in frequency to create the sound, a spectral glide, also known as "the wah effect". The wah-wah effect originated in the 1920s, with trumpet or trombone players finding they could produce an expressive crying tone by moving a mute in and out of the instrument's bell. This was later simulated with electronic circuitry for the electric guitar when the wah-wah pedal was invented. It is controlled by movement of the player's foot on a rocking pedal connected to a potentiometer. Wah-wah effects may be used as a fixed-filter to alter an instrument’s timbre ; they may be used when a guitarist is soloing; or, classically, they may be used to create a "wacka-wacka" funk-styled rhythm for rhythm guitar playing.
An envelope detector is an electronic circuit that takes a (relatively) high-frequency amplitude modulated signal as input and provides an output, which is the demodulated envelope of the original signal.
A voltage-controlled filter (VCF) is an electronic filter whose operating characteristics can be set by an input control voltage. Voltage controlled filters are widely used in synthesizers.
The Yamaha AN1x is a DSP-based analog modeling synthesizer, produced by Yamaha Corporation from 1997 to 1998, and was marketed as an "analog physical modelling control synthesizer".
Low-frequency oscillation (LFO) is an electronic frequency that is usually below 20 Hz and creates a rhythmic pulse or sweep. This is used to modulate musical equipment such as synthesizers to create audio effects such as vibrato, tremolo and phasing.
A phaser is an electronic sound processor used to filter a signal by creating a series of peaks and troughs in the frequency spectrum. The position of the peaks and troughs of the waveform being affected is typically modulated by an internal low-frequency oscillator so that they vary over time, creating a sweeping effect.
Electro-Harmonix is a New York City-based company that makes electronic audio processors and sells rebranded vacuum tubes. The company was founded by Mike Matthews in 1968. It is best known for a series of guitar effects pedals introduced in the 1970s and 1990s. EHX also made a line of guitars in the 1970s.
Octave effect boxes are a type of special effects unit which mix the input signal with a synthesised signal whose musical tone is an octave lower or higher than the original. The synthesised octave signal is derived from the original input signal by halving (octave-down) or doubling (octave-up) the frequency. This is possible due to the simple two-to-one relationship between the frequencies of musical notes which are separated by an octave. One of the first popular musicians to employ the octave effect was Jimi Hendrix, who also used a variety of other effects in his recordings and public performances. Hendrix used an octave-fuzz pedal known as the octavia.
Moogerfooger is the trademark for a series of analog effects pedals manufactured by Moog Music. There are currently eight different pedals produced; however, one of these models is designed for processing control voltages rather than audio signal. A sixth model, the Analog Delay, was released in a limited edition of 1000 units and has become a collector's item. Moog Music announced on August 28, 2018, that the Moogerfooger, CP-251, Minifooger, Voyager synthesizers, and some other product lines were being built using the remaining parts on hand and discontinued thereafter.
The Korg MS2000 is a virtual analog synthesizer produced by the Japanese electronic musical instrument manufacturer Korg.
Musitronics, often shortened to Mu-tron, was a manufacturer of electronic musical effects active in the 1970s. Founded by Mike Beigel and Aaron Newman, the company's products provided filtering and processing effects and were derived from synthesizer components. The company was known for producing high-quality products with many user-adjustable parameters, but high production costs and a failed product line, the Gizmotron, caused its downfall.
The Roland GR-500 is a guitar synthesizer. Manufactured by the Roland Corporation and FujiGen in 1977, it was one of the first guitar synthesizers.
The Korg Mono/Poly (MP-4) is a 44 key "mono-polyphonic" analog synthesizer manufactured by Korg from 1981 to 1984. This keyboard is the sister synthesizer to the Korg Polysix. It has four highly stable voltage-controlled oscillators (VCOs), a 4-pole, self-oscillating low pass filter (LPF), wide modulation capabilities and pseudo-polyphony (paraphony).
The Korg PS-3300 is a polyphonic analog synthesizer, produced by Korg between 1977 and 1981.
The AX60 is a polyphonic analogue keyboard synthesizer manufactured by Akai Professional in the mid-1980s. It was Akai's answer to the popular Roland Juno series synthesizers. The AX60 uses voltage-controlled analogue oscillators and filter circuitry based on the Curtis Electronics CEM 3394 integrated circuit.
Source Audio is a guitar effects pedal company based near Boston, Massachusetts. They produce modular effects pedals for electric guitar and bass, such as the Nemesis Delay, Ventris Dual Reverb, and Collider Delay+Reverb, as well as the C4 Synth, a modular rack synthesizer in pedal format, the Aftershock Bass Distortion, and the EQ2, a 10-band parametric equalizer with a plug-in style desktop interface. They are also the creators of the Hot Hand Wireless Effects Controller, a device worn around the finger that uses an accelerometer to send expression signal to an effect like an envelope filter. Source Audio mainly uses DSP to create their effects, and are known to program their own processor chips.
The Mu-Tron III is an envelope filter made by Musitronics Corporation. "The world's first envelope-controlled filter" was first made in 1972 by Mike Beigel and quickly became an essential effect for many funk musicians. It was produced again, in a modified version, in 2014.