1. Swell Pedal (Expression Pedal): Most organs have a swell pedal or expression pedal that controls the shutters of a swell box enclosing a group of pipes. Pressing the swell pedal gradually opens the swell box, increasing the volume of the enclosed pipes. It allows for a smooth crescendo or decrescendo effect while playing.
2. Tremulant and Voix Celeste: These are special stops that create a subtle wavering effect or a chorus-like sound, respectively. They add depth and movement to the sound of the organ and can help in emphasizing musical phrases or passages.
3. Registration Changes: Playing with different combinations of stops of varying volumes and tones enables the organist to achieve dynamic control. Selecting louder stops, such as full organs or reeds, naturally results in a more robust sound, while employing softer stops, such as flutes or strings, produces a delicate sound.
4. Touch and Fingering: Just like other keyboard instruments, the organist's touch and fingering can influence dynamics. Lighter touch and shallow key depression produce a softer sound, while heavier touch and deeper key depression lead to a louder and fuller sound. Additionally, skilled organists use techniques like legato (smooth and connected notes) and staccato (detached notes) to create rhythmic and dynamic accents.
5. Pedal Technique: In addition to manual dynamics, footwork on the organ (particularly with the bass pedals) can affect dynamics. Precise control of the pedals allows the organist to accentuate bass notes or play them more subtly to balance with the manuals.
By combining these techniques and effects, organists have the means to control the dynamics and expressivity of their performances, creating nuanced musical interpretations and conveying the emotional qualities of the music. Each unique composition is approached with attention to achieving appropriate dynamics based on the composer's intention and musical context.