Department of Building Physics, University of Stuttgart, Pfaffenwaldring 7, 70569 Stuttgart, Germany.
J Acoust Soc Am. 2012 Jan;131(1):739-48. doi: 10.1121/1.3651242.
In the sound spectrum of flue organ pipes in addition to the usual harmonic partials, sometimes a series of equidistant but not harmonic lines can be found. This phenomenon has been observed in the recorded sound of pipes from different pipe ranks. The second set of spectral lines is similar to "frequency combs" used in optics for accurate measurement of optical frequencies. Analysis of measured sound spectra with and without frequency comb and simulations are presented and discussed in the paper. The appearance of frequency combs in the sound spectrum is explained by a model that assumes the presence of a mouth tone in addition to the pipe sound. Mouth tone bursts are generated when the oscillating air jet passes the upper lip. The burst repetition frequency is locked to the fundamental frequency of the pipe and the bursts are coherent with a pulse-to-pulse phase shift. The phase shift explains the observed frequency offset of the frequency comb to the harmonic frequencies. The simulations also show that weak and fluctuating mouth tones cannot generate frequency comb due to a lack of coherence.
在风琴管的音谱中，除了通常的谐和泛音部分，有时还会发现一系列等距但非谐和的线条。这一现象在不同音管阶次的录音中都有观察到。第二组谱线类似于光学中用于精确测量光频率的“频梳”。本文展示并讨论了有和没有频梳的测量声音谱的分析和模拟。音谱中出现频梳的现象可以通过一个模型来解释，该模型假设除了管音之外还有口唇音的存在。当振荡的空气射流经过上唇时，会产生口唇音爆发。爆发的重复频率与管的基频锁定，爆发与脉冲到脉冲的相位差是相干的。相位差解释了观察到的频梳相对于谐频的频率偏移。模拟还表明，由于缺乏相干性，微弱和波动的口唇音无法产生频梳。
