Transients in Pipe Organ Tones

Abstract

A critical study of pipe organ sounds has been initiated by by recording transient and steady state waveforms and harmonic analyses of tones photographically from oscilloscope traces, with some magnetic tape recordings. Microphones are located from 34 to 112 in. from the mouth or open end of the pipe. Observations show that reed pipes usually reach maximum output in a fewer number of cycles than flue pipes, the number increasing with frequency at a rate less than proportional to frequency. Wave shape is roughly constant with time in reed pipes and in flue pipes with low harmonic content. Tones with higher harmonic content are usually initiated by an inexact harmonic, which grows and then often reduces in amplitude as the fundamental grows. In diapasons (open) this is second harmonic; in the Nason Flute (stopped) it is third. Third harmonic rise and early decay produces a “chiff” sound, less obvious with second harmonic. Reed pipe sounds approach impulse excitation of bandpass filters, with or without pronounced peaks. Flue pipes have peaked formants with regenerative excitation less rich in harmonics. The research objective must determine what is important in waveform as well as harmonic content, resulting in a better understanding of how we hear.