An
expression pedal is an important control found on many
organsThe organ , is a keyboard instrument of one or more divisions, each played with its own keyboard operated either with the hands or with the feet. The organ is a relatively old musical instrument in the Western musical tradition, dating from the time of Ctesibius of Alexandria who is credited with...
and synthesizers, as well as in the
pedal steel guitarThe pedal steel guitar is a type of electric guitar that uses a metal bar to "fret" or shorten the length of the strings, rather than fingers on strings as with a conventional guitar. Unlike other types of steel guitar, it also uses pedals and knee levers to affect the pitch, hence the name "pedal"...
, that allows the
volumeLoudness is the quality of a sound that is primarily a psychological correlate of physical strength . More formally, it is defined as "that attribute of auditory sensation in terms of which sounds can be ordered on a scale extending from quiet to loud."Loudness, a subjective measure, is often...
of the sound to be manipulated. Because the source of power with a
pipe organThe pipe organ is a musical instrument that produces sound by driving pressurized air through pipes selected via a keyboard. Because each organ pipe produces a single pitch, the pipes are provided in sets called ranks, each of which has a common timbre and volume throughout the keyboard compass...
and
electronic organAn electronic organ is an electronic keyboard instrument which was derived from the harmonium, pipe organ and theatre organ. Originally, it was designed to imitate the sound of pipe organs, theatre organs, band sounds, or orchestral sounds....
s is not generated by the organist, the volume of these instruments has no relationship with how hard its keys or pedals are struck; i.e., the organ produces the same volume whether the key or pedal is depressed gently or firmly. Moreover, the tone will remain constant in
pitchPitch is an auditory perceptual property that allows the ordering of sounds on a frequency-related scale.Pitches are compared as "higher" and "lower" in the sense associated with musical melodies,...
, volume, and
timbreIn music, timbre is the quality of a musical note or sound or tone that distinguishes different types of sound production, such as voices and musical instruments, such as string instruments, wind instruments, and percussion instruments. The physical characteristics of sound that determine the...
until the key or pedal is lifted, at which point the sound stops. The expression pedal gives the organist control over the external source of power, and thus the volume, of the instrument, while leaving his or her hands free. This system of dynamic control is completely distinct from the act of adding
stopsAn organ stop is a component of a pipe organ that admits pressurized air to a set of organ pipes. Its name comes from the fact that stops can be used selectively by the organist; some can be "on" , while others can be "off" .The term can also refer...
(in the case of pipe organs) or pulling more drawbars (in the case of digital organs and synthesizers). Furthermore, the expression pedal can influence the volume (and, to a lesser degree, the timbre) of a note while it is being played; unlike other instruments, in which the note typically decays after it is first sounded, the organist can increase the strength of a chord or note as it sounds by increasing pressure on the expression pedal.
The modern expression pedal itself is a large pedal, roughly resembling an oversized
automobileAn automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...
accelerator, either partially or fully recessed within the
organ consolethumb|right|250px|The console of the [[Wanamaker Organ]] in the Macy's department store in [[Philadelphia]], featuring six manuals and colour-coded stop tabs....
and located either directly above or to the right of the organ's pedalboard. As the pedal is pressed forward with the toes, the volume of the sound is increased; as it is depressed with the heel, the volume is decreased.
Pipe organs
Beginning in the nineteenth century, it became common for one or more divisions of pipes in a pipe organ to be
enclosed in a wooden box, at least one side of which would consist of palettes that open and close in a manner similar to a Venetian blind. A mechanical (later electrical) mechanism connected the box to a pedal that the organist would use to open and close the shutters, adjusting the perceived loudness of the sound. When the box is
shut (or
closed), less sound is released into the venue. In American and British organs, the enclosed division is usually named the
Swell, and the box surrounding the pipes is usually referred to as the
swell box. Thus, the expression pedal is sometimes known as the
swell pedal or
swell shoe. Larger organs may have two or more expression pedals, allowing the volume of different divisions to be individually controlled.
No matter how well a swell box is designed, the sound of the pipes is altered by their enclosure. Even when the shutters are fully opened, the pipes do not speak as clearly into the room as they would if they were otherwise unenclosed.
On pipe organs, the expression pedal should not be confused with the
crescendo pedalA crescendo pedal is a large pedal commonly found on medium-sized and larger pipe organs , either partially or fully recessed within the organ console. The crescendo pedal incrementally activates stops as it is pressed forward and removes stops as it is depressed backward...
, which progressively adds stops as it is opened.
Ratchet swell lever
Historically, the palettes were manipulated by a
ratchet swell, a lever operated by the foot to the side of the console. The lever would fit into two or three different notches, which would lock the position of the lever, and therefore the shutters, in place. To change the position of the shutters, the lever would be kicked sideways to allow it to travel into a new position. The lever was weighted so that its default position was at the top, with the shutters closed. As the lever was lowered, the shutters would open.
Balanced swell pedal
The
balanced swell pedal (as pictured above) was developed in the late nineteenth century so that the opening of the box could be fixed at any degree (not just the two or three options of the ratchet swell). This pedal is fitted above the center of the pedalboard. It usually rotates towards and away from the organist through a distance of about 90° from an almost vertical position ("shut") to a near horizontal position ("open"). Because the pedal is balanced, the organist does not need to hold it in position, and it will balance at any point in its travel. In addition, this location for most expression pedals, above the center of the pedalboard, is much more convenient for use by both feet if necessary (although it is usually operated with the right foot).
Correspondence to
The Musical TimesThe Musical Times is an academic journal of classical music edited and produced in the United Kingdom. It is currently the oldest such journal that is still publishing in the UK, having been published continuously since 1844. It was published as The Musical Times and Singing Class Circular until...
in 1916 debates the merits of both the ratchet lever and balanced pedal systems of expression. One writer suggests that balanced expression pedals are either too sensitive or not sensitive enough and are unable to produce effective sforzandos (though many improvements have been made since this letter was written), and that he knows many organists who are having balanced expression pedals removed. One organist most open to the change suggests that real crescendos and diminuendos are not possible with a ratchet swell lever, as the notches provided are always either just under or just above the required dynamic level. Furthermore, he states that the balanced expression pedal affords the ease of use of either foot, whereas the previous correspondent desired two ratchet levers, one at either side of the pedalboard.
Other expression technologies
In 1933, Aubrey Thompson-Allen created the "Infinite Speed and Gradation Swell Engine," based on the work of Father Henry Willis. The mechanism allowed for an infinitesimally slow as well as an instantaneous opening and closing of the swell shades. The spring-loaded expression pedal sits in what would be a half-open position on a normal balanced pedal. The mechanism opens the swell shades at a speed relative to how far the expression pedal is pressed. This uncommon device requires a completely different expressive technique than the balanced expression pedal. It is found on very few organs.
Reed organs and harmoniums
Reed organA reed organ, also called a parlor organ, pump organ, cabinet organ, cottage organ, is an organ that generates its sounds using free metal reeds...
s and
harmoniumA harmonium is a free-standing keyboard instrument similar to a reed organ. Sound is produced by air being blown through sets of free reeds, resulting in a sound similar to that of an accordion...
s of the late nineteenth and early twentieth centuries featured a pair of bellows pedals at the base of the instrument. When the pedals were pumped up and down, air was drawn across the organ’s reeds, producing sound. This capability made the harmonium widely available to homes and small churches, though the dynamic range tended to be limited (not to mention that the organist would eventually tire from pumping). However, these free-reed organs had several ways of controlling their volume and expression. Unlike a pipe organ with a blower, the wind pressure of the reed organ can be directly controlled by varying the speed the bellows are operated with the feet, providing a means of producing softer or harsher tones. Harmoniums (where the bellows provided a positive pressure) usually had an air reservoir to reduce the effort needed to pump the bellows when many stops were engaged. However, some instruments had a system to bypass the reservoir if the player wanted more direct control. Reed organs often had a form of swell shutter mechanism. The bellows system and reed ranks were contained in a wooden frame. By covering this frame, a swell box was created. A single shutter in the top of the box, inside the organ case, allowed the volume to be controlled. Since the player's feet were needed to operate the bellows, the swell shutter was controlled by a lever operated by the player's knee. The lever operated horizontally, and the player pushed their knee towards the side of the instrument to open the shutter. The lever returned to the 'closed' position on a spring or a locking mechanism could be enagaged to hold the shutter open.
Subsequently, the electrically powered reed organ, and later the
electronic organAn electronic organ is an electronic keyboard instrument which was derived from the harmonium, pipe organ and theatre organ. Originally, it was designed to imitate the sound of pipe organs, theatre organs, band sounds, or orchestral sounds....
, allowed the bellows pedals to be replaced with an expression pedal, allowing the organist to effect a more substantial change in volume more easily than was possible with the manually pumped instrument.
Electronic organs
The style of popular organ music of the 20th and 21st centuries such as
jazzJazz is a musical style that originated at the beginning of the 20th century in African American communities in the Southern United States. It was born out of a mix of African and European music traditions. From its early development until the present, jazz has incorporated music from 19th and 20th...
is highly dynamic and requires constant use of the expression pedal in a fashion very different from that of
classical organ literatureThe organ repertoire consists of music written for the organ. Because it is one of the oldest musical instruments in existence, written organ repertoire spans a time period almost as long as that of written music itself. The organ's solo repertoire is among the largest for any musical instrument...
. This tendency increased with the arrival of spinet organs and modern synthesizers, which offset the expression pedal and reduced the size of the pedalboard. These changes allowed the organist to keep the right foot constantly on the expression pedal, while playing the pedalboard with only the left foot. This ability encouraged organists to operate the expression pedal more often during playing. To take advantage of this style of playing, some expression pedals on modern electronic organs are equipped with toe switches, which allow the organist to make quick registration changes without removing the foot from the pedal.
Expression pedals may be non-linear in response, meaning that slight pressure changes may cause a greater proportional change in volume than a more complete depression. In this regard, each organ tends to be rather distinct.
Guitars and Digital Effects
Many popular electric guitar effects such as wah, vibrato and swell use a variable pedal control similar to a keyboard expression pedal. Historically these have been built into dedicated pedals for each effect, but modern digital amplifiers and processors allow many different effects to be built into a single, small floor or rack mount unit. Special built in, or plug in expression pedals can be used with these devices to allow control of multiple effects with a single expression pedal. Using the expression pedal, the musician can not only emulate dedicated effects such as wah, but also have real time control of almost any variable such as volume, tone, echo repeats, effect speed etc. Some guitar expression pedals include integrated toe switches similar to those for some electric organs. The switches provide even more control allowing the musician to turn effects on and off, and switch between different amplifiers.