How do organ stops change the sound of a pipe organ?

On a pipe organ, a stop is a mechanism that controls the entry of pressurized air into a specific rank of pipes, allowing the organist to select which sets of pipes will sound when a key is pressed. Because the tone of an individual pipe is immutable, stops are essential for varying the instrument's sound.12

Stops change the sound of the organ in several ways:

• Tone Colour: Each stop governs a distinct rank of pipes, each with its own unique tonal quality. By drawing different stops, the organist changes the overall timbre of the instrument.13
• Pitch and Texture: Mutation stops sound at intervals other than unison (such as a fifth higher), which adds an incisive quality to the sound when combined with unison pipes. Mixture stops engage multiple ranks of pipes simultaneously, creating a richer, more complex texture.1
• Combinations: Organists can combine multiple stops to create diverse registrations, allowing for the prominence of a melody against an accompaniment or the rapid alternation between loud and soft passages.3

By engaging or disengaging these ranks, the organist transforms the organ from a simple instrument into a versatile, composite one.3