There are two types of action that determine which pipes will sound: the stop action, and the key action. These may be mechanical (in older organs, and increasingly in modern ones) or electric; other types of action used mainly historically include tubular-pneumatic and electro-pneumatic. Another type of action is the combination action triggered by pistons.

This term is also used to describe the touch characteristics of a keyboard.

Use of the same rank in more than one division to reduce the number of pipes required. See Borrowed Stop.

The term given to the puff of wind produced when a pipe starts to speak (which sounds something like a cough). In an organ with mechanical key action, it can be controlled by varying the force with which the key is hit.

A means of combining two divisions of the organ by uniting keyboards. See Coupler.

The English word for principal, used for an open flue stop of medium scale (synonymous with open diapason). It is also commonly used to denote the scale of a flue as medium (rather than flute or string), even though the stopped diapason is flute-scale. Grove's third definition (out of four) is: In classical British organ terminology, 'the diapasons' (Stopped and Open) form the foundation upon which the Great Organ flue choruses may be built. See Principals.

A set of stops normally associated with a keyboard, but may also be a floating division. See Division.

Normally found only on large organs, this is a division that is not normally connected to a keyboard, but may be connected to the required keyboard when needed by means of a Coupler.

A flue pipe of wide scale. See Flutes.

A series of integer multiples of the fundamental frequency; the presence of these give musical instruments their specific timbre. See Harmonics.

One of the two actions of the organ, operated by the keys on the manuals and pedals. See Stop and Key Actions.

Another name for kneeboard.

An organ keyboard for the hands. See Manuals.

An organ stop comprising several ranks. See Mixture.

A flat (not raised) note on a keyboard (usually white on a manual). See Keyboards.

A button under the keys of a manual typically used to activate a pre-recorded stop combination. See Thumb Pistons.

The number of voices that sound at once. In a pipe organ, this is the number of pipes that speak simultaneously. In a virtual organ (where multi-rank stops such as mixtures count as a single voice) it is the number of stop/note samples that are to be handled simultanously; this also includes release samples that contain the reverberation once the pipe has stopped speaking.

An organ that can be moved, and would normally have ranks no greater than 4' physical length. Also used for a division of an organ that produces a similar sound.

A flue pipe of medium scale, in between flute (wide scale) and string (narrow scale). Also the standard stop name for that type. See Principals. In English, commonly called diapason.

A row of pipes producing the same type of sound. See Rank.

The art (unique to organists) of creating an appropriate sound by combining the available stops. Also refers to the selected combination(s) of stops. See Stop.

The set of recorded sound samples, and other data such as images and the organ definition used to implement a virtual organ. See Sample Sets.

The diameter of a flue pipe in relation to its speaking length. This is the most important factor in determining the timbre of the pipe.

A control found with the Stop Controls that is involved with the stop action (i.e. in opening one or more ranks of pipes).

One of the two actions of the organ, operated by the stop controls on the console. See Stop and Key Actions.

A flue pipe of narrow scale. See Strings.

A pedal that allows the volume of an enclosed division to be changed by opening and closing the shutters of the swell box.

(also Toe Piston) This has the same function as a piston, except it is operated by the feet.

Mechanical key action, in which key presses are transmitted by means of rods of wood, aluminum, or other material.

An organ stop comprising two ranks, one slightly detuned of the other. See Undulating.

A large valve that opens/closes the airway to a wind chest. In a few organs (especially late 19^th century French ones), this could be operated by a pedal to turn on/off a set of stops such as reeds and mixtures.

This is an organ that generates sound by combining in real time recorded samples from one (or possibly multiple) real organs. See Why a Virtual Organ?.

The pressurized air fed to the pipes. Wind pressure is normally measured in inches of water. It is typically around 3", but may be much higher (up to 100") for some reeds.