Sound is what you hear. I hope you aren’t satisfied with that answer. A sound engineer needs to understand not only what they hear, but what happens with sound.
Sound comes from vibration. Think of hitting a drum cymbol. These vibrations cause fluctuations in the air pressure called sound waves. Think of ripples in a pond. Each ripple has a peak height and depth. One complete motion (up and down) of a sound wave is a cycle. The height of a wave is the distance from the bottom depth to the peak – that’s the amplitude. Here comes a little practical application. Amplitude determines the volume of a sound. The greater the amplitude, the greater the sound. Going with the ripple in a pond analogy, small ripples equal low volume.
We now know vibration causes sound and volume is determined by the height of the sound waves. What makes a sound unique? Frequency. Frequency is the change in rate of air pressure. That’s also known as pitch. The human ear can hear vibrations that are at a frequency of 20Hz (Hertz) to 20K Hz. Greater than 20K Hz drives dogs nuts and less than 20 Hz is a vibration that we feel but cannot hear.
Oh, I see. You want practical application. Who doesn’t want practical application? It’s like this…if you understand frequency, you understand how an equalizer (EQ) works and how to make it work for you. A typical soprano hits frequencies between ~260 Hz and ~1150 Hz. Setting the EQ for a soprano means modifying the EQ settings between these ranges to match how the singer would sound without a microphone. Remember, you want people to sound good but not so much better than they really are that is sounds unnatural. The most logical conclusion would be ranges outside of the 260-1150 could be cut out. Not so fast. Those sound waves that were first discussed – they are a composite of different frequencies (pitches). However, science is cool and our bodies are amazing. Therefore we introduce yet another term: harmonics. Harmonics are the different frequencies for the same object. I can’t think of a good water analogy so think of harmonics like ingredients in a recipe. Each has it’s distinct flavor and texture but it’s not until these ingredients are mixed do we get a final flavor and texture.
That’s sound in a very wordy nutshell.
Now for how sound works with electronics. A voice talks into a microphone and that sound turns into an audio signal. This audio signal is then passed from component to component as an electrical representation created by fluctuating current. The amplitude of this signal is known as signal volume. Once the signal makes it to the speakers, it’s converted to sound.
Did you know that sound adds together? Signals from the same source are added together within a mixer. These signals can be “in phase” or “out of phase.” If two microphones are recording the same person at the same distance & direction from the source, they are in phase. Sound = good. If one microphone is instead picking up the sound as it’s reflected off a wall (time delayed) then the two signals are out of phase. Sound = not good.
Finally, we have decibels. Decibels are a tenth of a bel. That’s not a joke. bel comes from “alexander graham bell.” A bel represents a ratio between two power levels. One bel corresponds to a perceived difference of ~2 times the sound level. Rustling leaves are around 10 dB, an average conversation is 60 dB, and a gunshot is around 145dB. Our “threshold of pain” is around 125. Explains why marksmen use protective hearing gear at the firing range. Here is where the ratio aspect of a dB comes into play. A 0 dB point can be set in relation to a specific level. For example, 0 dB could be set to match room noise of a restaurant. Then, 10 dB isn’t 10 dB like we think of feet or inches. It’s 10 dB on top of that ~50 dB of room noise.
This section is an overview of sound and sound terminology. If you understand these terms, you’ll start understanding proper mixer usage, proper component settings, and reading sound articles will be much much easier. Heck, you might be able to write one yourself.