Following Stewart, a discussion of the application of the principle of uncertainty (ΔνΔl≈ 1) to sound phenomena is given. Various sound phenomena are thereby explained and certain related experiments with frequency vibrato are reported. The phenomena explained are: The chromatic glissando imitation of a portamento, analysis of a formant into a Fourier series, the relation between vibrato wideness and pitch range and the pleasing effect of a frequency vibrato.