Sound for movies is like pictures for movies. Something happens in front of a microphone or camera lens, a whole bunch of magic stuff happens, then sound and picture happens from the speakers and on the screen of a cinema theater.
Obviously, the title Listen To This means that we’ll discuss the grand subject of sound. It may seem that sound is not as important or complex as moving pictures, but this is not true. It will take several articles to point out the different ingredients so we can fulfill our objective: to know how to tell what is right and wrong about the sound we are given in the theater auditorium. But it will be worth it to know, since we all want to get the most out of our entertainment experience…and money.
Let’s start with a simple explanation.
Sound is an energy made from a vibration. That vibration is created by something moving. That movement causes the air near it to move. That moving air causes the air next to it to move, which moves the air next to it . Actually, the movement – the vibration – can go through other things in addition to air. The sound vibrations can start in, and travel through, water or jello or dust or wood or metal. You can prove this yourself: knock on a piece of wood while you feel the wood a short distance away. You can feel the vibrations. If you hold your ear to the wood, you can hear the vibrations.
But notice: the wood at the first position is (where you knocked) is not moving to the place where you listened. This is different from some other kinds of energy, like the wind. Wind is the actual particles of air moving from one area to another.
When energy is transferred from one particle to the next, instead of the particle actually moving through a space, it is called a wave…because it takes the form of a wave. Which is great because we can look at big waves, then apply what we know to small waves.
Let’s begin with waves on the beach. The most simple thing to do wit them is to count the number of waves that come to the shore in a minute. Depending on where you are and what is happening, the number might be 10 or 15 or 20, but may be even as low as 6. And the next minute it will usually be different than the first.
Waves on the ocean are caused by wind blowing over the top of the water. Friction causes the top layer of water to move and eventually the particles of water transfer that energy of the wind to other particles of water until the energy moving in the water is far away from the energy of the source. In fact the storm that caused the wind might be finished. Eventually, the energy in the water gets pushed up by the angle of the shore, and crashes. Maybe later we can talk about the sound wave that it makes. But the important thing now is to remember that that the energy of the wave came from somewhere distant, and it has a frequency…that is, number of waves in a minute.
Let’s take a break…with Physics Girl
OK, now we know some things about waves and we have seen that they also have something to do with sound. Actually, waves have a lot to do with sound.
Let’s go back to our ocean waves. On a certain day, we notice that the frequency of the waves is 15 or 20 waves per minute. A science person would say that this is 15 or 20 cycles per minute. If we drop a rock into a pool of water, you can also see the waves, and you can also count their frequency. You might also notice that there are several waves spaced apart from each other at a certain distance. If you measure the top of one wave to the top of another, you have what is called their wavelength.
It is a lot more difficult to see or count the wavelength or cycles of sound. You can tap on or pluck the lowest string on a piano with 88 keys and watch the string vibrate. If the piano is in tune, the lowest string will vibrate at a little faster than 27 times every second. In the past, a science person would say, 27 and a half cycles per second. But we don’t use the “cycles” term anymore. Now we say use a special term, Hertz, named after Mr. and Mrs. Hertz’ son, Heinrich Hertz. Young Heinrich was the person who proved much of the theory about waves to be true. Now, they say that the low note of the piano is 27.5 Hertz, which is abbreviated as 27.5 Hz.
A person who plays the piano doesn’t think about frequencies, they call that bottom note A…or more technically, A0. A1 is an octave higher, and an octave higher is twice the frequency. For A1 this is 55 Hz, and then the next octave is 110 Hz, then 220, then 440, which is a special note. It is the note that you hear when you hear an orchestra tuning up. It is also called the A above middle C. If you keep doubling for each octave, you run out of A notes at 3,520 Hz, which is A7. There are a few piano notes higher, going up to 4186 Hz.
The frequencies of the female human voice also end in that same area of 4,000 Hz, while male voices begin in the area of 500 or 1,000 Hz. Other sounds are spread above and blow – up to 16 or 20 thousand hertz, and down to 20 hertz.
But we don’t have singers singing in the movie theater, or actual bombs going off either. We have speakers that are powered by amplifiers that are playing back a recording.
The speakers work on the same principle: the material of the speaker vibrates which moves some air which moves some other air, and on and on until we have waves of air hitting the walls or the ceiling or the seats…or our human ears.
Descriptions of the ear and eyes for the human hearing and visual systems will come at another time, but it shouldn’t surprise you to know that they are extremely complicated devices and they include portions of the brain. All we need to discuss right now is that they have the ability to do the opposite of what the speakers do. Parts of the ear are able to physically move in a way that can create electrical signals to the brain for different frequencies.
In summary, some audio happens near a microphone, something inside the microphone moves in response and with some magic turns into an electrical signal. Editors and mixers play with that sound and eventually it turns from electricity to movement of a speaker and then back to waves in the air and then waves in your ear.
We will spend some time with light and color next, then come back to sound and talk about power and mixing and we’ll get the first steps of what to listen for.
Questions?