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.[1] The term can also be used for film cinematography or theatre lighting in much the same way (see fade (filmmaking) and fade (lighting)).

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.

Though relatively rare, songs can fade out then fade back in. Some examples of this are "Helter Skelter" and "Strawberry Fields Forever" by The Beatles,[5] "Suspicious Minds" by Elvis Presley,[6] "Shine On Brightly" by Procol Harum, "Sunday Bloody Sunday" by John Lennon and Yoko Ono, "That Joke Isn't Funny Anymore" by The Smiths,[7] "Thank You" by Led Zeppelin,[5] "It's Only Money, Pt. 2" by Argent, "The Great Annihilator" by Swans, "(Reprise) Sandblasted Skin" by Pantera, "Illumination Theory" and "At Wit's End" by Dream Theater, "Future" by Paramore, "Doomsday" by MF Doom, "Outro" by M83, "Cold Desert" by Kings of Leon, and "The Edge Of The World" by DragonForce.

## History

### Origins and early 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. Esterhazy appears to have understood the message, allowing the musicians to leave.[8]

Gustav Holst's "Neptune, the mystic", part of the orchestral suite The Planets written between 1914 and 1916, is another early example of music to have a fade-out ending during performance.[9] 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".[10] 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".[11]

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.[12]

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.[13] 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.

### Types

• 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.[4]
• 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.[4]
• Introduction under speech: The music is placed at the specified time on the cue, the level must be low in order for the vocals to be audible.[4] Here the fade-up generally occurs just before the final words in order for the cue to be given.[4] In stage productions the closing music is played from a predetermined time and fades up at the closing words in order to fit in exactly with the remaining program time.[4]

### Contemporary

No modern recording can be reliably identified as "the first" to use the technique. In 2003, on the (now-defunct) website Stupid Question, John Ruch listed the following recordings as possible contenders:

Bill Haley's cover version of "Rocket 88" (1951) fades out to indicate the titular car driving away. There are claims that The Beatles' "Eight Days a Week" (recorded 1964) was the first song to use the reverse effect—a fade-in. In fact, The Supremes had used this effect on their single "Come See About Me", issued a little over a month before "Eight Days a Week".

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."[14]

### Shapes

The shape of a regular fade and a cross-fade can be shaped by an audio engineer.[2] Shape implies that you can change the rate at which the level change occurs over the length of the fade.[2] Different types of preset fades shapes include linear, logarithmic, exponential and S-curve.[2]

#### S-curve

The S-curve shape is interesting since it has qualities that correlate with the previously mentioned curves.[2] The level of the sound is 50% at the midpoint, but before and after the midpoint the shape is not linear. There are also two types of S-curves. Traditional S-curve fade-in has attributes of the exponential curve can be seen at the beginning; at the midpoint to the end it is more logarithmic in nature.[2] A traditional S-curve fade-out: is logarithmic from the beginning up to the midpoint, then its attributes are based on the exponential curve from the midpoint to the end.[2] This is true for the situation in reverse as well (for both fade-in and fade-out).[2] Cross-fading S-curves works as follows; it diminishes the amount of time that both sounds are playing simultaneously.[2] This ensures that the edits sound like a direct cut when the two edits meet - this adds an extra smoothness to the edited regions.[2]

DJ Qbert in Rainbow Warehouse in Birmingham (Video with close-up photography at the DJ mixer, though without sound). From 1:36, heavy use of the crossfader can be seen.

There are many software applications that feature virtual cross-fades, for instance, burning-software for the recording of audio-CDs. Also many DAW's (Pro Tools, Logic exc.) have this function. Cross-fade is normally found on samplers and usually based on velocity.[20] The purpose of a cross-fade it to utilize a smooth changeover between two cut pieces of audio.[2] Velocity cross-fading can be incorporated through a MIDI transformation device and where more than one note can be assigned to a given pad (note) on the MIDI keyboard; velocity cross-fading may be available.[20]

These types of cross-fades (those that are based on note velocity) allow two (even more) samples to be assigned to one note or range of notes.[21] This requires both a loud and soft sample; the reason for this is Timbre change.[21] This type of cross-fade is quite subtle depending on the proportion of the received note velocity value of the loud and soft sample.[21]

Cross-fading usually involves the sounding of a combination of one or two sounds at the same time.[20] While cross-fading one does not want the second part of the fade to start playing before the first part is finished; one wants the overlapping parts to be as short as possible. If edit regions are not trimmed to a zero-crossing point one will get unwelcome pops in the middle.[2] A sound at the lowest velocity can fade into a sound of a higher velocity, in the order of: first the first sound then the second.[20] All possible without fading out the sounds that are already present.[20] This in turn is a form of Layering that can be used in the mix.[20] The same effect (as was created with velocity) can be applied to a controller.[20] This allows continued monitored control; the cross-fading function can also be controlled on some instruments by the keyboard position.[20] These sounds on the MIDI keyboard can be programmed.

Cross-fades can either be applied to a piece of music in real time, or it can be pre-calculated.[3] Grandmaster Flash has been credited with the invention of the first cross-fade by sourcing parts from a junkyard in the Bronx.[22] 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 commercial documented example was designed by Richard Wadman, one of the founders of the British company Citronic. It was called the model SMP101, made about 1977, and had a crossfader that doubled as a L/R balance control or a crossfade between two inputs.[23]

When cross-fading two signals that are being combined (mixed), 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 mix, special shapes must be used, called "equal power" (or "constant power") shapes. 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 mid point of the mix 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 ${\displaystyle {\sqrt {mix}}}$ and ${\displaystyle {\sqrt {1-mix}}}$ (where mix ranges from 0 to 1).[24][25][26]

Equal power shapes typically have the sum of their curves (in the middle of the mix range) exceeding the nominal maximum amplitude (1.0), which may produce clipping in some contexts. If that is a concern, then "equal gain" (or "constant gain") shapes should be used (which may be linear or curved) 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 cross-fade shapes, particularly for equal power shapes.

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 also called a ‘pot’.[4] A contact can move from one end to another. As this movement takes place the resistance of the circuit can either increase or decrease.[4] At one end the resistance of the scale is at 0 and at the other side it is infinite.[4] A. Nisbett explains the fader law as follows in his book called The Sound studio:"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".

A knob which rotates is usually not considered a fader, although it is electrically and functionally equivalent. Some small mixers use knobs rather than faders, as do a small number of DJ mixers designed for club DJs who are creating seamless mixes of songs. A fader can be either analogue, directly controlling the resistance or impedance to the source (e.g. a potentiometer); or digital, numerically controlling a digital signal processor (DSP). Analogue faders are found on mixing consoles. A fader can also be used as a control for a voltage controlled amplifier, which has the same effect on the sound as any other fader, but the audio signal does not pass through the fader itself.

### Digital

The console's computer will update the console's controls on playback.[27] This will be done from memory at the same speed.[27] The advantage of working with mix automation is that only one engineer can perform the job with minimal effort;[27] it can be set up or recorded beforehand to make it even simpler.[16] An example of this is when Ken Hamman installed linear faders that made it possible for him to alter several channels with one hand while mixing, thus he assumed an interactive role in the process of recording.[28] This type of fader level adjustment is also called ‘riding’ the fader.[16]

### Types

Many DJ equipment manufacturers offer different mixers for different purposes, with different fader styles, e.g., "scratching", beatmixing, and cut mixing. High-priced mixers often have crossfade curve switches allowing the DJ to select the type of crossfade necessary. Experienced DJs are also able to crossfade between tracks using the channel faders.

These functions will be found on a primary monitor function.[29] This pre-fade listen is valuable since it allows one to listen through headphones in order to hear what the pre-faded part sounds like, while the studio loudspeaker is being used to monitor the rest of the program.[4]

Pre-fade listen can also be used for talkback as well as to listen to channels before they have been faded.[4] After-fade listen only gets its information later.[4] The choice of listen or level will depend on the user's interest: either with the quality and/or content of the signal or with the signal's level. PFL takes place just before the fader and has a joint channel and monitoring function.[29] PFL sends the channel's signal path to the pre-fade bus.[29] The bus is picked up in the monitor module and made accessible as a substitute signal that is sent to the mixer output.[29] Automatic PFL has been made available, almost universally, and no longer needs to be selected beforehand.[29]

Pre-fade listen can also be incorporated in radio stations and serves as a vital tool. This function allows the radio presenter to listen to the source before it is faded on air; allowing the presenter to check the source's incoming level and make sure it is accurate.[29] It is also valuable since live radio broadcasts can fall apart without it as they will not be able to monitor the sound. After-fader listen is not as useful in live programs.[29]

## References

1. ^ Nisbett, Alec (1966). The Technique of the sound studio. Focal Press.
2. Langford, S. 2014. Digital Audio Editing. Burlington: Focal Press. pp. 47-57.
3. Rumsey, F. & McCormick, T. 1992. Sound and Recording. Burlington: Focal Press. pp. 241, 282-284.
4. Nisbett, A. 1962. The Technique of the Sound Studio. London & New York: Focal Press.
5. ^ a b Everett, Walter (2008). The Foundations of Rock: From "Blue Suede Shoes" to "Suite: Judy Blue Eyes". Oxford University Press. p. 171. ISBN 978-0-19-531023-8.
6. ^ Patterson, Nigel; Piers Beagley. "'Suspicious Minds': Elvis' Greatest Single?". Elvis Information Network. Retrieved September 2, 2010.
7. ^ Goddard, Simon (2009). Mozipedia: The Encyclopedia of Morrissey and The Smiths. London: Ebury Press.
8. ^ Symphony No. 45 (Haydn)
9. ^ Huron, David (2006). Sweet Anticipation: Music and the Psychology of Expectation. MIT Press. p. 318. ISBN 0-262-08345-0.
10. ^ "The Planets" (full orchestral score): Goodwin & Tabb, Ltd., London, 1921
11. ^ "The Great Composers and Their Music", Vol. 50, Marshall Cavendish Ltd., London, 1985. I.H. as quoted on p1218
12. ^ Kopiez, Reinhard; Platz, Friedrich; Müller, Silvia; Wolf, Anna (2015). "When the pulse of the song goes on: Fade-out in popular music and the pulse continuity phenomenon" (PDF). Psychology of Music. 43 (3): 359–374. doi:10.1177/0305735613511505. S2CID 147398735. Archived from the original (PDF) on 2020-02-12.
13. ^ "Stupid Question Archive". Archived from the original on 2007-11-30. Retrieved 2008-01-11.
14. ^ Middleton, Richard (1990). Studying popular music (Reprint ed.). Philadelphia: Open University Press. pp. 95–96. ISBN 0-335-15275-9.
15. ^ a b Moylan, W. 2002. The Art of Recording. United States of America: Focal Press.
16. ^ a b c Langford, S. 2011. The Remix Manual. Burlington: Focal Press. pp. 54-55, 202-205.
17. ^ "Archived copy". Archived from the original on 2015-04-08. Retrieved 2015-04-14.{{cite web}}: CS1 maint: archived copy as title (link)
18. ^
19. ^ a b Jeffs, Rick (1999). "Evolution of the DJ crossfader". RaneNote 146. Rane Corp. Retrieved 6 July 2013.
20. Pressing, J. 1992. Synthesizer Performance and Real-Time Techniques. United States of America: Oxford University Press. pp. 61, 69, 246-249, 386.
21. ^ a b c d Rumsey, F. 1994. MIDI Systems & Control. Oxford: Focal Press.
22. ^ "Awesome Men Throughout History: Grandmaster Flash". 14 August 2012.
23. ^ "Evolution of the DJ Crossfader". Archived from the original on 2002-08-03.
24. ^ The Art of Digital Audio Recording A Practical Guide for Home and Studio, Steve Savage, 2011, Oxford University Press, pp 127-130
25. ^ HackLab: An Introduction to Computer Programming and Digital Signal Processing in MATLAB, Eric Tarr, 2018, Taylor & Francis, pp 112-122
26. ^ For examples of some commonly used crossfade shapes, see https://math.stackexchange.com/questions/4621/simple-formula-for-curve-of-dj-crossfader-volume-dipped
27. Roads, A. 1996. The Computer Music Tutorial. United States of America: Library of Congress Cataloging-in-Publication Data. pp. 378-379.
28. ^ Braun, H. J. Music and Technology in the Twentieth Century. London: The Johns Hopkins University Press.
29. Talbot-Smith, M. 1994. Audio Engineer’s Reference Book. Oxford: Reed Educational and Professional Publishing Ltd, 1999.