Acoustical Analysis of Initial Transients in Flute Like Instruments

Time frequency analysis of sounds produced during the initial transients of flute like instruments, (recorders and organ pipes) show that the build-up of the different harmonics of the steady state sounds is preceded by a group of acoustical phenomena – noises, inharmonic tones – which are very important for the perceived quality of the transients. In this paper, initial transients produced by a complete flue pipe instrument (mouth tones) are compared with those produced by the same mouthpiece disconnected from the pipe (edge tones) on several instruments: organ pipes and recorders. Mouth tones from the initial transients of a complete instrument are, just like edge tones, mainly controlled by the mouth parameters: speed of jet at flue exit; and distance between flue exit and labium; they therefore correspond to self-oscillation of the mouth. During pressure build-up and when frequencies coincide, mouth tones can stabilise on one resonant mode of the pipe, creating an inharmonic forerunner which has been observed by many authors. In general, mouth tones, which are due to "mouth behaviour" of the jet, disappear as soon as the regular steady state is established. However, a paradoxical functioning where mouth tones and harmonics of the first mode are coexisting is sought for when voicing a specific organ stop: the viola 4' of the Italian organ. The musical relevance of mouth tones is discussed for the recorder as well as when voicing specific organ stops.