Spectrogram of a recorded breathing sound. The spectrogram shows the spectro-temporal features of an air intake (left) and output (right) in a single breathing-sound cycle. Frequency-modulated, ultrasonic tonal components can be observed during air intake. These components result from turbulences in the nasal cavity during depression. Note the good signal-to-noise ratio, which was realizable with the recording equipment described in the methods.
Gröger and Wiegrebe BMC Biology 2006 4:18 doi:10.1186/1741-7007-4-18