4) Basics: Audio (Sound)

Sound is all around us. We don’t need any particular talent to use it. Doctors tell us that we can hear sounds in the womb.

Using sound well is a different story. Being able to judge sound so it is the best possible for your clients is another different story.

For a simple definition, “Sound” is what we hear. But actually every sound involves hundreds of steps. These steps start with a motion that occurs at one point. You can think about it like a pebble that is thrown into a pond.

Quickly, that one motion starts a series of motions that spread out as waves – like a circular wave on the water of the pond when a pebble is thrown in. There are two main differences with the water analogy though. First is that the pond surface is a flat surface – our sound wave is different – it goes out in all directions like light from a flame. The second difference is that the spreading wave is the energy spreading out, pushing the air.

The energy of the wave eventually reaches our ears. It then goes inside the ears and finally (through a process that is so sophisticated that it seems like it must be magic), the wave motion turns into electricity that goes down some nerves.  That new energy wave then transmits the original motion to the brain for analysis.

Sometimes the word Sound and the word “Audio” seem like they mean the same thing. But they can be different. We will say that “audio” is a type of sound that is being played through some equipment. This is the sound that we hear in the movie auditorium. Grammar in English is complicated though, so it is not always true. We will say that the sound of his voice onscreen was pleasant – we won’t say, the ‘audio’ of his voice. And, we won’t say that the voice of the singer on the street had amazing ‘audio’. Instead, we would say that the ‘sound’ of his or her voice was amazing.

Whether the sound is natural or reproduced, the path to our ears is complex. You don’t need to know about most of that complexity. But you should understand enough so that you aren’t fooled by something that isn’t immediately obvious. Your job is to tell the technician about changes in the sound…in particular, changes that sound worse…and why. So, we’ll start slow, and cover the basics and when you hear more in the auditorium with the test DCPs, you can review the material here as often as you like. And, you can ask questions.

The Audio portion of a movie comes out of many speakers around the auditorium.

Most of the time there are 3 speakers behind the screen called Left Front (LF), Center Front (CF) and Right Front (RF). Usually those speakers are spread out across the screen, closer to the top than across the center, and pointed slightly downward toward the center of the room. On the side walls and back walls are the Left Surround and the Right Surround speakers.

Finally, there is a speaker (or set of speakers) that handle the extreme low frequencies. These are called the Low Frequency Effect speakers, and abbreviated, LFE.

Those 6 sets of speakers (around the room in a circle, LF, CF, RF, RSurr, LSurr and LFE) are called a 5.1 system.

There is a variation of the 5.1 system called the 7.1 system. The difference between 5.1 and 7.1 is simple – the speakers on the rear wall in a 7.1 system have a separate amplifier system for those right and left rear speakers (instead of being part of the Left Surround and Right Surround systems.)

In those simple statements there is a lot of unsaid information.

For example, when the word speaker is used, it probably means a box, or even two or three boxes. Each box might have 1 of 2 or 3 speakers in them. Speaker design is an art as much as a science, and designing an auditorium is an art, and putting together all the parts is an art. So, we aren’t going to spend time on all the different designs or the reasons, except to say that some can be louder, some can be louder at certain for certain frequencies. Basically, you need to know that if someone says “I have to replace the speaker in the Left Front of Auditorium 5”, they probably mean part of the speaker system, not the whole thing. You might here it called a speaker driver or element or component. Making loud sounds all day is hard business, and these pieces wear out.

And now it has been said, our first real technical word: Frequency.

Frequency is a term that is used when describing both sound and light. So we will need to get a good idea of it, and we’ll do that in Part 2 of the Basics of Sound. But let’s cover it a little bit just to get a feel and not end with a mystery.

Sound frequencies are very easy to think of when we consider a musical instrument like the piano. From left to right, the notes start with the low and rumbling sounds and and go all the way up to the twinkling high notes. If you look at the longest strings of the piano as they are hit, you can almost see the back and forth slower motion as they move the air and create those low notes that hit our ears. Not so much for the faster moving strings of the high notes.

What does that have to do with frequency? Well, frequency is the number of times that something happens, compared with a unit of time. I saw my friend quite frequently…about once a week, for example. Once per second I am able to type a word…the frequency is one word per second. The strings on the lowest note on the piano – the one on the far left – goes back and forth 27 and a half times every second. We say that it has a frequency of 27.5 cycles per second. Some of the notes in the middle of the piano go back and forth over 400 times per second – the ‘A’ note above middle ‘C’ is 440 cycles per second. The very highest strings vibrate at over 4,000 cycles per second.

Don’t forget to write questions or thoughts in the Comments or in the Contact Form. Let us know what we could explain better, or didn’t explain at all.

Thanks…and until next time, keep a steady beat.


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