Phase and Familiarity
Phase is the interaction of two tones generated simultaneously. So far we've been talking about pure tones, which actually don't occur naturally in nature. So what do we hear in nature?
Complex tones occur in nature. They are combinations of pure tones, much like a brick wall is composed of bricks.
One difference is that the bricks in a wall are all the same size. The pure tones in a Complex tone are all different sizes, or more correctly, frequencies.
Not just any two pure tones will combine, moreover. They must be integral multiples of each other, like 125 Hz, 250 Hz, 500 Hz and 1000 Hz etc.
Actually if two pure tones of the same frequency and intensity are produced simultaneously, they will combine. If they are in phase (i.e.,the molecules move in the same direction at the same time) the result will be only one pure tone that is louder.
If two pure tones of the same frequency and intensity occur simultaneously out of phase, they will cancel each other out.
If two pure tones are produced simultaneously, but are directly out of phase (i.e., the molecules of air are moving in exactly the opposite direction) the result will be no sound at all! That is because all the energy is cancelled out.
For example, if I am pulling on a table and you are pushing on it equally hard; and then I push on it and you pull on it equally hard, the end result will be no movement of the table.
In some auditoriums that have not been carefully acoustically designed, you can be sitting right in the front row and hear hardly anything because you are in a "dead spot" (I.e., a spot where the sound bouncing off the walls reflects back out of phase an
There are delay feedback mechanisms now on the market, which play back environmental noises out of phase creating almost a quiet world for an individual who wears the earphones.
If two pure tones of different frequencies occur simultaneously they will cause fluctuations in the smooth curve to create a Complex tone.
These noise suppressors are reminiscent of Maxwell Smarts "Cone of Silence," (if you are old enough to remember the TV show "Get Smart.")
On the other hand, I have an unconfirmed report that there is a spot in the U.S. Senate Chambers where sounds are reflected back in phase and amplify confidential whispers made across the room.
What happens if the to two simultaneous pure tones are different frequencies and are integral multiples of each other?
Obviously, they can't cancel each other out. But they do combine in an alternating enhancing and inhibitory fashion.
The end result is that the smooth curve of the sine wave (pure tone) becomes bumpy. If more pure tones are added (being all integral multiples) the curve becomes even more bumpy. This now describes a Complex Tone.
NOTES: ÉAnd here is another example and discussion of Complex Tones versus Pure Tones.
The Fundamental in a Complex tone determines the pitch, and the pattern of Overtones determines the quality.
If one starts with a Complex tone it is possible (if you are a math nerd) to tease out and identify the pure tones that originally combined to create the sound. That process is called Fourier Analysis.
Through this analysis we would discover that a complex tone has an array of pure tones, each having a different frequency. The lowest frequency is called the Fundamental. Whatever it is, determines the pitch of the sound we hear.
All of the other (higher) frequencies are called overtones.
They form a particular pattern, like 4 8 16 thousand cycles or, 4, 16, 32 etc. Whatever that pattern is determines the quality of the sound. It is the quality that makes a sound recognizable or familiar.
Even our voice has a particular pattern of overtones that makes us sound like us. They have been referred to as Voice Prints.
It is the pattern of overtones that are changed in a process called resonation (we will talk about that later) to produce the different vowel sounds of speech.
Let's look now at the source of all these vibrations, and how mass and tension play an important role in more ways than one.