A phaser is an audio signal processing technique used to filter a signal by creating a series of peaks and troughs in the frequency spectrum. Audio signal processing, sometimes referred to as audio processing, is the processing of a representation of auditory signals, or Sound. An audio filter is a type of filter used for processing Sound signals. The position of the peaks and troughs is typically modulated so that they vary over time, creating a sweeping effect. In Telecommunications, modulation is the process of varying a periodic Waveform, i For this purpose, phasers usually include a low frequency oscillator. The term low-frequency oscillation (LFO is an audio signal usually below 20 Hz which creates a pulsating rhythm rather than an audible tone
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Process
The electronic phasing effect is created by splitting an audio signal into two paths. One path treats the signal with an all-pass filter, which preserves the amplitude of the original signal and alters the phase. An all-pass filter is an Electronic filter that passes all frequencies equally but changes the phase relationship between various frequencies The amount of change in phase depends on the frequency. When signals from the two paths are mixed, the frequencies that are out of phase will cancel each other out, creating the phaser's characteristic notches. Changing the mix ratio changes the depth of the notches; the deepest notches occur when the mix ratio is 50%.
The definition of phaser typically excludes such devices where the all-pass section is a delay line; such a device is called a flanger [1]. Flanging is a time-based Audio effect that occurs when two identical signals are mixed together but with one signal time-delayed by a small and gradually changing amount Using a delay line creates an unlimited series of equally spaced notches and peaks. It is possible to cascade a delay line with another type of all-pass filter as in [2], this combines the unlimited number of notches from the flanger with the uneven spacing of the phaser.
Structure
Traditional electronic phasers use a series of variable all-pass phase-shift networks which alter the phases of the different frequency components in the signal. An all-pass filter is an Electronic filter that passes all frequencies equally but changes the phase relationship between various frequencies A quadrature booster, also known as a phase-shifting transformer or more simply a quad booster, is a specialised form of Transformer used to control the These networks pass all frequencies at equal volume, introducing only phase change to the signal. Human ears are not very responsive to phase differences, but this creates audible interferences when mixed back with the dry (unprocessed) signal, creating notches. In physics interference is the addition ( superposition) of two or more Waves that result in a new wave pattern The simplified structure of a mono phaser is shown below:
The number of all-pass filters (usually called stages) varies with different models, some analog phasers offer 4, 8 or 12 stages. An all-pass filter is an Electronic filter that passes all frequencies equally but changes the phase relationship between various frequencies Digital phases may offer up to 32 or even more. This determines the number of notches/peaks in the sound, affecting the general sound character. A phaser with a stages of n generally has n/2 notches in the spectrum, so a 4-stage phaser will have two notches.
Additionally, the output can be fed back to the input for a more intense effect, creating a resonant effect by emphasizing frequencies between notches. This involves feeding the output of the all-pass filter chain back to the input, as shown here:
The frequency response of an 8-stage phaser with or without feedback is shown. Note that the peaks between the notches are sharper when there's feedback, giving a distinct sound.
A stereo phaser is usually two identical phasers modulated by a quadrature signal; the output of the oscillators for the left and right channels are a quarter-wave out of phase. Stereophonic sound, commonly called stereo, is the reproduction of Sound, using two or more independent audio channels through a Symmetrical The phase of an oscillation or wave is the fraction of a complete cycle corresponding to an offset in the displacement from a specified reference point at time t = 0
Most modern phasers are a part of a digital signal processor, often trying to emulate analog phasers. A digital signal processor ( DSP or DSP micro) is a specialized Microprocessor designed specifically for Digital signal processing, generally Phasers are mostly found as plugins for sound editing software, as a part of a monolithic rackmount sound effect unit, or as "stompbox" guitar effects. A stomp box or stompbox is a simple Percussion instrument consisting of a small wooden box placed under the foot which is tapped or stamped on rhythmically to
Phaser audio effect
Usage
Phasing is a popular effect for electric guitar. An electric guitar is a type of Guitar that uses pickups to convert the vibration of its steel-cored strings into an electrical current which is made louder The term was often used to refer the original tape flanging effect heard on many psychedelic records of the late 1960s, notably "Itchycoo Park" by the Small Faces, and "Pictures of Matchstick Men" by Status Quo. Flanging is a time-based Audio effect that occurs when two identical signals are mixed together but with one signal time-delayed by a small and gradually changing amount Psychedelic music is a term that refers to a broad set of popular music styles genres and scenes that may include Psychedelic rock, psychedelic folk, Psychedelic The 1960s decade refers to the years from the beginning of 1960 to the end of 1969 "Itchycoo Park" is a Psychedelic pop song written by Steve Marriott and Ronnie Lane of the group Small Faces. Small Faces were an English rock group from East London, heavily influenced by American Rhythm and blues. " Pictures of Matchstick Men " was the first hit single by Status Quo, released in January of 1968 Status quo is a Latin term meaning the present existing state of affairs or "the state in which" Eddie Van Halen often used a phaser as part of his signal chain, after his distortion effects, including the amplifier itself: Van Halen used a power attenuator to bring the amp's output down to line level so he could put effect boxes after it. Edward Lodewijk "Eddie" Van Halen (born January 26 1955 is a Dutch Guitarist, Keyboardist, Songwriter and producer Phasing is primarily responsible for the soaring and unique guitar sounds Brian May achieved with the band Queen in such songs as Bohemian Rhapsody. Brian Harold May, CBE is a Song written by Freddie Mercury and originally recorded by the band Queen for their 1975 album ''A Night at the Opera''.
Many electronic keyboard instruments like the Rhodes and the Clavinet are commonly treated with a phaser to "sweeten" their sounds. A keyboard instrument is any musical instrument played using a Musical keyboard. A Rhodes piano is an electromechanical Musical instrument, a brand of Electric piano. A Clavinet is an electrophonic Keyboard instrument manufactured by the Hohner company Examples can be heard in Billy Joel's "Just The Way You Are", Styx's "Babe" and Paul Simon's "Still Crazy After All These Years. William Martin Joel (born May 9 1949 is an American Pianist and Singer-songwriter. Styx ( pronounced: /stɪks/ is an American Rock band. Their hit songs have included " Come Sail Away " " Babe " " Paul Frederic Simon (born October 13 1941 is an American Songwriter, Musician, and member of the Rock and Roll Hall of Fame. "
In motion picture or television production, the effect created by a phaser is often used to imply that the sound is synthetically generated, like turning a natural human voice into a computer or robot voice. Television ( TV) is a widely used Telecommunication medium for sending ( Broadcasting) and receiving moving Images, either monochromatic
The technique works because the frequency filtering produces sound we associate with mechanical sources, which only generate specific frequencies, rather than natural sources, which produce a range of frequencies. A vocoder is a different effect used for similar purposes. A vocoder, ˈvoʊkoʊdər (a Portmanteau of vox/voc ( voice) and encoder) is an analysis / synthesis system mostly used for speech in which the input is
Similar effects
A specific type of phasing, flanging is a similar effect, in which the notches are linearly spaced. Flanging is a time-based Audio effect that occurs when two identical signals are mixed together but with one signal time-delayed by a small and gradually changing amount In a flanger effect, the notches are created by mixing the signal with a delayed version of itself. Delay is an Audio effect which records an input signal to an audio storage medium, and then plays it back after a period of time Flangers tend to sound more natural, like the "jet plane whoosh" effect, whereas phasers tend to sound more otherworldy. For comparison of the two effects, check flanging. Flanging is a time-based Audio effect that occurs when two identical signals are mixed together but with one signal time-delayed by a small and gradually changing amount
See also
External links
- Phase shifting article on Harmony Central
- Photos of Vintage Pedals & Effects
- Photos of New & Vintage Phaser-Pedals
- The technology of phase shifters and flangers
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