thumb|upright|[[Audio mixer faders in a London pub.]]
In audio engineering, a fade is a gradual increase or decrease in the level of an audio signal. The term can also be used for film cinematography or theatre lighting in much the same way (see fade (filmmaking) and fade (lighting)).
In sound recording and reproduction, a song may be gradually reduced to silence at its end (fade-out), or may gradually increase from silence at the beginning (fade-in). Fading out can serve as a recording solution for pieces of music that contain no obvious ending. Quick fade-ins and -outs can also be used to change the characteristics of a sound, such as to soften the attack in vocal plosives and percussion sounds.
Professional turntablists and DJs in hip hop music use faders on a DJ mixer, notably the horizontal crossfader, in a rapid fashion while simultaneously manipulating two or more record players (or other sound sources) to create scratching and develop beats. Club DJs in house music and techno use DJ mixers, two or more sound sources (two record players, two iPods, etc.) along with a skill called beatmatching (aligning the beats and tempos of two records) to make seamless dance mixes for dancers at raves, nightclubs and dance parties.
History
Origins and examples
Possibly the earliest example of a fade-out ending can be heard in Joseph Haydn's Symphony No. 45, nicknamed the "Farewell" Symphony on account of the fade-out ending. The symphony, which was written in 1772, used this device as a way of courteously asking Haydn's patron Prince Nikolaus Esterházy, to whom the symphony was dedicated, to allow the musicians to return home after a longer-than-expected stay. This was expressed by the players extinguishing their stand candles and leaving the stage one by one during the final adagio movement of the symphony, leaving only two muted violins playing. Esterházy appears to have understood the message, allowing the musicians to leave.
Gustav Holst's "Neptune, the mystic", part of the orchestral suite The Planets written between 1914 and 1916, is another early example of music having a fade-out ending during performance. Holst stipulates that the women's choruses are "to be placed in an adjoining room, the door of which is to be left open until the last bar of the piece, when it is to be slowly and silently closed", and that the final bar (scored for choruses alone) is "to be repeated until the sound is lost in the distance". Although commonplace today, the effect bewitched audiences in the era before widespread recorded sound—after the initial 1918 run-through, Holst's daughter Imogen (in addition to watching the charwomen dancing in the aisles during "Jupiter") remarked that the ending was "unforgettable, with its hidden chorus of women's voices growing fainter and fainter ... until the imagination knew no difference between sound and silence".
The technique of ending a spoken or musical recording by fading out the sound goes back to the earliest days of recording. In the era of mechanical (pre-electrical) recording, this could only be achieved by either moving the sound source away from the recording horn, or by gradually reducing the volume at which the performer(s) were singing, playing or speaking. With the advent of electrical recording, smooth and controllable fadeout effects could be easily achieved by simply reducing the input volume from the microphones using the fader on the mixing desk. The first experimental study on the effect of a fade-out showed that a version of a musical piece with fade-out in comparison to the same piece with a cold end prolonged the perceived duration by 2.4 seconds. This is called the "Pulse Continuity Phenomenon" and was measured by a tapping-along task to measure participants’ perception of pulsation.
An 1894 78 rpm record called "The Spirit of '76" features a narrated musical vignette with martial fife-and-drum that gets louder as it nears the listener, and quieter as it moves away. There are early examples that appear to bear no obvious relationship to movement. One is "Barkin' Dog" (1919) by the Ted Lewis Jazz Band. Another contender is "America" (1918), a patriotic piece by the chorus of evangelist Billy Sunday. By the early 1930s, longer songs were being put on both sides of records, with the piece fading out at the end of side one and fading back in at the beginning of side two. Records at the time held only about two to five minutes of music per side. The segue allowed for longer songs (such as Count Basie's "Miss Thing"), symphonies and live concert recordings.
However, shorter songs continued to use the fade-out for unclear reasons—for example, Fred Astaire's movie theme "Flying Down to Rio" (1933). Even using fade-out as a segue device does not seem obvious, though we certainly take it for granted today. It is possible that movies were an influence here. Fade-ins and fade-outs are often used as cinematic devices that begin and end scenes; film language that developed at the same time as these early recordings. The term fade-out itself is of cinematic origin, appearing in print around 1918. And jazz, a favorite of early records, was a popular subject of early movies too. The same could be said for radio productions. Within a single programme of a radio production, many different types of fade can be applied. When mixing from speech to music, there are a few ways that fade can be used. Here are three examples.
- Straight: the introduction has become a musical link between the music/speech that follows; additionally, the first notes of the intro can be emphasized to make it pop out more.
- Cutting the introduction: Since the first word of the vocals has to follow promptly after the cue light, it could be used to move the recording onward. "Suspicious Minds" by Elvis Presley, "Shine On Brightly" by Procol Harum, "Sunday Bloody Sunday" by John Lennon and Yoko Ono, "That Joke Isn't Funny Anymore" by The Smiths, "Thank You" by Led Zeppelin,
More recently: "At the meta-song level, the prevalence of pre-taped sequences (for shops, pubs, parties, concert intervals, aircraft headsets) emphasizes the importance of flow. The effect on radio pop programme form [is] a stress on continuity achieved through the use of fades, voice-over links, twin-turntable mixing and connecting jingles."
Fade
A fade can be constructed so that the motion of the control (linear or rotary) from its start to end points affects the level of the signal in a different manner at different points in its travel. If there are no overlapping regions on the same track, regular fade (pre-fade / post-fade) should be used. A smooth fade is one that changes according to the logarithmic scale, as faders are logarithmic over much of their working range of 30-40 dB. however this is also something it can do. The perceived distance increase can be attributed to a diminishing level of timbral detail, not the result of a decreasing dynamic level.
Shapes
The shape of a regular fade and a crossfade can be shaped by an audio engineer. Shape implies that you can change the rate at which the level change occurs over the length of the fade. Different types of preset fades shapes include linear, logarithmic, exponential and S-curve. or an inverse-logarithmic ratio. This curve more closely matches human hearing, with finer control at lower levels, increasing dramatically past the 50% point. Since the perceived volume of a sound has a logarithmic relationship with its level, the logarithmic fade sounds consistent and smooth over the whole duration of the fade. This makes this curve useful for fading standard pieces of music. It is best used on a long fade-out since the fade has a perceived linear nature. Also, a fade-out sounds very neutral when incorporated to parts of music with natural ambience. In crossfades, this type of curve sounds very natural. When this curve is applied, the perceived volume of the fade's midpoint is at about 50% of the maximum – when the two sections are summed, the output volume is fairly constant.
The technique of crossfading is also used in audio engineering as a mixing technique, particularly with instrumental solos. A mix engineer will often record two or more takes of a vocal or instrumental part and create a final version which is a composite of the best passages of these takes by crossfading between takes.
There are many software applications that implement crossfades, for instance, burning-software for the recording of audio-CDs and most DAWs have this function and is available on samplers. The purpose of a cross-fade is to create a smooth changeover between two pieces of audio. The samples represent the timbre of the sampled instrument at loud and soft levels. they typically had separate faders for each channel. Grandmaster Flash is often credited with the invention of the first crossfader by sourcing parts from a junkyard in the Bronx. It was initially an on/off toggle switch from an old microphone that he transformed into a left/right switch which allowed him to switch from one turntable to another, thereby avoiding a break in the music. However, the earliest documented commercial example was designed by Richard Wadman, one of the founders of the British company Citronic. The model SMP101 mixer, made about 1977, had a crossfader that doubled as a L/R balance control or a crossfade between two inputs.
Crossfade shapes
When crossfading two signals, the two fade curves can employ any of the shapes listed above (see #Shapes), such as linear, exponential, S-curve, etc. When the goal is to have the perceived loudness of the combined mix signal stay fairly constant across the full range of the crossfade, special equal power shapes must be used. Equal power shapes are based on audio power principles, particularly the fact that the power of an audio signal is proportional to the square of the amplitude. Many equal power shapes have the property that the midpoint of the fade provides an amplitude multiplier of 0.707 (square root of one half) for both signals. A variety of equal power shapes are available, and the optimal shape will generally depend on the amount of correlation between the two signals. An example pair of curves that keep power equal across the mix are <math>\sqrt{m}</math> and <math>\sqrt{1 - m}</math>, where m is the crossfade position and ranges from 0 to 1.
Equal power shapes typically have the sum of their amplitude (in the middle of the crossfade) exceeding the nominal maximum amplitude (1.0), which may produce clipping in some circumstances. If that is a concern, then equal gain shapes should be used that are designed so the two curves always sum to 1.
In the digital signal processing realm, the term power curve is often used to designate crossfade shapes, particularly for equal power shapes.
== Fader ==<!--Fader (audio engineering) and Audio fader redirect here-->
thumb|3 faders used as graphic equalizer in a personal cassette player
A fader is any device used for fading, especially when it is a knob or button that slides along a track or slot. It is principally a variable resistance or potentiometer. A contact can move from one end to another. As this movement takes place, the resistance of the circuit can either increase or decrease. At one end the resistance of the scale is at 0 and at the other side, it is infinite. "The law of the fader is near-logarithmic over much of its range, which means that a scale of decibels can be made linear (or close to it) over a working range of perhaps 60 dB. If the resistance were to increase according to the same law beyond this, it would be twice as long before reaching a point where the signal is negligible. But the range below -50 dB is of little practical use, so here the rate of fade increases rapidly to the final cut-off".
The advantage of working with mix automation is that only one engineer can perform the job with minimal effort. If a send mix is configured pre-fader, then changes to the main channel strip fader do not affect the send mix.
On an analogue mixing console, the PFL (pre-fader listen) switch routes the incoming signal of a channel to a PFL bus. This bus is sent to the monitor mix and/or the headphones mix, allowing for monitoring an incoming signal before it is sent to the main output. When the mixer is equipped with VU meters, the PFL allows to visually monitor an audio source without hearing it and adjust its input gain.