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 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. Common effects include distortion/overdrive, often used with electric guitar in ele ...

typically used with

electric guitar An electric guitar is a guitar that requires external amplification in order to be heard at typical performance volumes, unlike a standard acoustic guitar (however combinations of the two - a semi-acoustic guitar and an electric acoustic gui ...

bass guitar The bass guitar, electric bass or simply bass (), is the lowest-pitched member of the string family. It is a plucked string instrument similar in appearance and construction to an electric or an acoustic guitar, but with a longer neck and ...

clavinet The Clavinet is an electrically amplified clavichord invented by Ernst Zacharias and manufactured by the Hohner company of Trossingen, West Germany, from 1964 to 1982. The instrument produces sounds by a rubber pad striking a point on a tension ...

, and

electric piano An electric piano is a musical instrument which produces sounds when a performer presses the keys of a piano-style musical keyboard. Pressing keys causes mechanical hammers to strike metal strings, metal reeds or wire tines, leading to vibrations ...

etc. The distinctive choppy rhythm guitar sound on many

funk Funk is a music genre that originated in African American communities in the mid-1960s when musicians created a rhythmic, danceable new form of music through a mixture of various music genres that were popular among African Americans in the m ...

and

disco Disco is a genre of dance music and a subculture that emerged in the 1970s from the United States' urban nightlife scene. Its sound is typified by four-on-the-floor beats, syncopated basslines, string sections, brass and horns, electric pia ...

recordings from the 1970s popularized the effect.

Operation

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.''The Boss Book: The Ultimate Guide to the World's Most Popular Compact Effects for Guitar'', 2002, Hal Leonard Corporation 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. 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 An envelope detector (sometimes called a peak 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. ...

to produce a voltage representing the overall volume of the input. This signal is then used to sweep the

cutoff frequency In physics and electrical engineering, a cutoff frequency, corner frequency, or break frequency is a boundary in a system's frequency response at which energy flowing through the system begins to be reduced ( attenuated or reflected) rather than ...

of a filter. The filter usually has a

low-pass A low-pass filter is a filter that passes signals with a frequency lower than a selected cutoff frequency and attenuates signals with frequencies higher than the cutoff frequency. The exact frequency response of the filter depends on the filter des ...

bandpass A band-pass filter or bandpass filter (BPF) is a device that passes frequencies within a certain range and rejects (attenuates) frequencies outside that range. Description In electronics and signal processing, a filter is usually a two-port ...

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 Red Hot Chili Peppers are an American rock music, rock band formed in Los Angeles in 1983, comprising vocalist Anthony Kiedis, bassist Flea (musician), Flea, drummer Chad Smith, and guitarist John Frusciante. Their music incorporates element ...

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.

Notable examples

The first envelope-controlled filter built for musical instruments was the Mu-Tron III, invented by Mike Beigel. Other examples include the MXR Envelope Filter and the Boss AW-2 Auto Wah (LFO controlled).

Grateful Dead The Grateful Dead was an American rock music, rock band formed in 1965 in Palo Alto, California. The band is known for its eclectic style, which fused elements of rock, Folk music, folk, country music, country, jazz, bluegrass music, bluegrass, ...

guitarist

Jerry Garcia Jerome John Garcia (August 1, 1942 – August 9, 1995) was an American musician best known for being the principal songwriter, lead guitarist, and a vocalist with the rock band Grateful Dead, which he co-founded and which came to prominence ...

is known for extensive use of an envelope filter (particularly the Mu-Tron III), examples being his playing on "Estimated Prophet" and "

Shakedown Street ''Shakedown Street'' is the tenth studio album by rock band the Grateful Dead, released November 15, 1978, on Arista Records. The album came just over a year after previous studio album '' Terrapin Station''. It was the final album for Keith and ...

Phish Phish is an American rock band formed in Burlington, Vermont, in 1983. The band is known for musical improvisation, extended jams, blending of genres, and a dedicated fan base. The band consists of guitarist Trey Anastasio, bassist Mike Gordon ...

guitarist

Trey Anastasio Ernest Joseph "Trey" Anastasio III (born September 30, 1964) is an American guitarist, singer, and songwriter, best known as the lead guitarist of the rock band Phish, which he co-founded in 1983. He is credited by name as composer of 152 Phish o ...

also frequently uses the effect, especially in addition to the use of distortion. The guitar solo in "

What I Am "What I Am" is a song written by Edie Brickell and Kenny Withrow and recorded by Edie Brickell & New Bohemians for their debut album, ''Shooting Rubberbands at the Stars'' (1988). The song is highlighted by a guitar solo that notably features an ...

" by

Edie Brickell & New Bohemians Edie Brickell & New Bohemians is an alternative rock jam band that originated in Dallas, Texas, in the mid-1980s. The band is widely known for their 1988 hit "What I Am" from the album ''Shooting Rubberbands at the Stars''. Their music contains ...

features an auto-wah effect.

References

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