The register swell (also roller , roll swell or crescendo step ) is a playing aid (mechanical, pneumatic or electric) built especially for organs from the Romantic era , with which you can automatically pull or push the stops in such a way that the volume increases or decreases overall. Most of the time, the cuff is operated by a roller that is turned with the foot; a balancing step is also possible. In some organs, "self-running" rollers or automatic crescendos as foot pistons are occasionally possible. Most of the time, the order of the stops is determined by the organ builder, but newer instruments also have freely adjustable stop swellings.
The entire dynamic range of the organ can be easily controlled with the crescents , but unlike the swell box , no “smooth” crescendo or decrescendo is possible. In addition, the organist loses control over the timbre if the crescents are used exclusively.
The stop swell became common in the middle of the 19th century with the development of the symphonic organ.
- Wolfgang Adelung: Introduction to organ building . Breitkopf & Härtel, Wiesbaden 1979, p. 156.