# How is a human whistle a pure sine wave?

According to Wikipedia human whistling is a pure sine wave.

If that is true and if a human is whistling and produces a rhythm like any song, is he still producing a pure sine wave?

For example, if I am producing a tone of any music through my whistle would it still be a pure single harmonic sinusoidal wave?

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Playing with a microphone and an oscilloscope a long time ago, I found that a continuous "mmmmmmmmmmmm" in a medium to high pitch falsetto intonation is very similar to a pure sine... – heltonbiker Nov 24 '12 at 16:08
Maybe this would be better on physics.SE – endolith Nov 25 '12 at 0:13
Even if you could produce a pure sine wave whistling (see other answers for why this is BS), it would only be truly pure if you never stopped. – learnvst Nov 28 '12 at 23:32

This is only an approximation!

• While the sound of whistling has a very prominent first harmonic, the other harmonics are still present too; there's a non-harmonic noise component; and the first harmonic is more a narrow bump than a sharp line. A better description of the sound of whistling would be white noise filtered through a band-pass filter with a very high Q, and sent through a slight waveshaper adding harmonics. With a slight modulation of amplitude and filter frequency.
• A pure sine wave is a stationary signal, it has constant frequency and constant amplitude. If you observe a whistling sound on a window larger than a few tenths of seconds, you will observe modulations in frequency (because of the melody and articulations between notes), and modulations in amplitude (as you breath and start/end notes).
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White noise through a high Q bandpass filter is not really what's happening though, is it? The sound of a successful whistle is much louder than the white noise that's produced by failed whistling. – endolith Nov 24 '12 at 17:44
I am not qualified to comment on what is happening - but I know that the white noise > high Q filter is commonly used to synthesize whistling-like sounds. – pichenettes Nov 24 '12 at 17:48

When you whistle, your mouth acts as a Helmholtz resonator: the movement of the air past your lips is causing pressure disturbances that cause the mass of the air inside your mouth to oscillate on its own compliance (like a spring-bob oscillator). The frequency produced is determined by the volume of air and its density, as well as its bulk modulus (mass and stiffness).

Broadband noise is also produced by the rushing of turbulent airflow past your lips; this might excite higher harmonics, but the amplitude of the resultant vibration at these frequencies is likely to be very low.

Certainly if you do an STFT of whistling at a single frequency and plot as a waterfall plot or colour map, it looks very much like there is a single frequency only.

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Here is a picture of me whistling into the FFT Spectrum Analyzer app on my android. Center-line is 1.2k Hz.

Notice the overwhelming strength of the first harmonic. Also note that while there is a second harmonic, it is about 20 to 40 times weaker than the first harmonic.

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