There are musical sounds, like the tones that I can produce with my violin, and there are noises, like the sound of my bike, riding through the snow. I suppose that many people would fail to perceive the latter as a specific musical tone. Why actually? What actually distinguishes these two sounds? What makes them seem so different?
1. John Powell (physicist and composer) on the physics of music (Science Friday).
A musical note is just a noise that appears regularly.
2. All noises are sounds, but by (1) a musical note (=tone) is a special kind of sound, because a sound can appear regular or irregular.
3. Now, by (1) and (2) we know, only a sound that appears regular will be perceived as a musical note. Then all sounds that appear irregular must be the so called ‘white noise‘. But then what does it mean for a sound to appear regular or irregular?
a. Sound is vibration transmitted through a solid, liquid, or gas; particularly, sound means those vibrations composed of frequencies able to be detected by ears.
b. Vibration refers to mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road.
c. The frequency [of a vibration] is inversely proportional to wavelength of a sound. The frequency f is equal to the phase velocity v of the wave divided by the wavelength λ of the wave.
5. Ok, henceforth by (2) and (4) musical sounds and white noise are mechanical vibrations. And the frequency with which a vibrations reach our ear is determined by its wavelength and its speed.
Hence if I understand correctly, a sound then appears regular, if the waves that reach our inner ear cause a periodic vibration of the hair cells, which given (4.b) and (4.c) means that the waves must be of equal wavelength/speed. In this case our braininterpreter tells us that we hear a musical note. While on the other hand, the waves that, when reaching the ear, cause a random tilting, are of different wavelengths/speed. And these sounds, therefore, appear irregular and will be interpreted as white noise?
Seems plausible to me. It would also mean that for example my violin is produced in such a way, that it produces sound waves of equal wavelengths, which is in fact true. The sounds on the other hand of my bike riding through the snow might produce many waves of different length and distance, which, for obvious reasons, also seems very likely. But then why is speech most of the time not directly perceived as a musical sound? An effect of the combination of pulses and pitch, together with the communication task it must also account for???