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An organ stop (or just stop) is a component of a pipe organ that admits pressurized air (known as ''wind'') 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" (admitting the passage of air to certain pipes), while others can be "off" (''stopping'' the passage of air to certain pipes). The term can also refer to the control that operates this mechanism, commonly called a stop tab, stop knob, or drawknob. The term is also sometimes used as a synonym for register, referring to rank(s) of pipes controlled by a single stop. Registration is the art of combining stops. ==Mechanics== Organ pipes are physically organized within the organ according to note and timbre, into sets. A set of pipes producing the same timbre for each note is called a ''rank'', while each key on a pipe organ controls a ''note'' which may be sounded by different ranks of pipes, alone or in combination. The use of stops enables the organist to selectively turn off ("stop") certain ranks in order to produce different combinations of sounds, as opposed to hearing all sounds simultaneously. While nowadays one speaks of "drawing" a stop to select a particular rank, the earliest organs were constructed as blockwerk with all ranks 'on' by default. The mechanism used to operate the stops varies widely, but the principle is the same: the stop control at the console allows the organist to select which ranks of pipes will sound when a key is pressed. When the organist desires a rank to sound, he or she operates the corresponding control at the console, allowing wind to flow to the pipes. Likewise, the organist can deny wind to the pipes by operating the same control in the opposite direction. Common stop controls include ''stop knobs'', which move in and out of the console, and ''stop tabs'', which toggle back and forth in position. Some organs, particularly smaller historical organs from England or Spain,〔James Dalton, "Iberian organ music before 1700," in ''The Cambridge Companion to the Organ'', ed. Nicholas Thistlethwaite and Geoffrey Webber (Cambridge: Cambridge University Press, 1998), 165.〕 feature ''divided registers'', in which there are two stop knobs for certain ranks. One stop knob will control the upper portion of the keyboard, and the other will control the lower portion of the keyboard. This arrangement allows the upper portion of the keyboard to sound a different registration than the lower portion, which lends a greater versatility to smaller organs, especially those with only one manual. Ranks which are neither divided nor extended (see below #Unification and extension) contain as many pipes as there are keys on the keyboard to which they are assigned: in most cases 61 pipes for a rank assigned to a manual and 32 pipes for a rank assigned to the pedal. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Organ stop」の詳細全文を読む スポンサード リンク
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