Frank Hergert (Hochschule Koblenz / Univ. of Appl. Sciences) - Organ pipes: their sound spectra and tonal timbre

A pipe organ may contain thousands of pipes, grouped into ranks. Each rank of pipes belongs to a certain family of organ. The tonal timbre within each rank may vary smoothly across its tonal compass.

A simple empirical model describing the steady part of the sound spectra has been developed and applied to various ranks. This allows for extracting typical features of different tone families and deriving timbre parameters to classify the organ tone.

The combination of high-pitched ranks yielding Mixture stops follows rules that have evolved over centuries. They can partly understood in terms of avoided acoustic roughness and adjusting a certain brightness of the combined spectra.

Special attention is devoted to low bass tones as numerous technical inventions facilitate to include them into pipe organs when building space is restricted. But what does a listener perceive when tones with frequencies below 33 Hz appear in musical context? Possibly, it is the acoustical roughness that substitutes for tonal pitch and mimicks the timbre expected for such low bass tones.