- Tom Kelly
12. Frequency, Wavelength, and the Speed of Sound: the Science of Sound 101
You can't master your craft until you've mastered the fundamentals ten times over. This week's episode is all about the fundamentals. What is sound? How does it travel from one place to another? What is wavelength and how does it correspond to a frequency?
All of these questions are answered within the episode, but I strongly feel that visuals are a very important part of learning, so let's tackle a few of these principals below.
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WHAT IS SOUND?
Sound is nothing more than a vibration that travels through a liquid, gas, or a solid. In terms of podcasting, we're talking about gas, or air molecules. Think of a speaker. The cone of the speaker moves in and out which causes the air particles closest to it to vibrate and bump into its neighboring air particle. This happens over and over again causing pockets of high pressure with many particle interactions, or compressions, and pockets of low pressure with few interactions as particles shift back to their original location, or rarefactions. It's important to know that the air surrounding your speaker doesn't physically get pushed towards you, just a minuscule amount, enough to hit its neighboring particle, and we call this a sound wave.
WHAT IS FREQUENCY?
This is a word more people have heard in their life, but not in the context of audio. Most can deduce that is must have something to do with how often something occurs, and most people would be right! In audio, the frequency refers to amount of compressions and rarefactions per second. In the image below, we see the distance between rarefactions (negative amplitude, low pressure) called a "Period". This term refers to the distance between peaks or the distance between troughs, which is the completion of 1 cycle. So when we say "cycles per second", we're talking about how many time we complete 1 cycle of peak, to trough, back to peak in one second, which is also called "Hertz". Now that may be a term you've heard before...
Let's look at 2 frequencies. Let's just say 100Hz and 1000Hz, or 1kHz (one kilohertz). A 100Hz wave will complete far fewer cycles in the same amount of time than a 1kHz wave, and this is illustrated below. The higher a frequency, the higher number you will see in Hertz (Hz), which refers to how many cycles per second take place in that tone.
WHAT IS WAVELENGTH
Low frequency waves (think of the bass in your car) have fewer cycles per second that higher frequencies. This means their periods are much longer, which we refer as a longer wavelength, which again, refers to the physical distance it takes for a single frequency to complete 1 cycle of peak to peak, or trough to trough.
This concept is more relevant to acoustics than it is to mixing a podcast, but again, we need to understand the fundamentals before we can move ahead and learn how to properly EQ vocals!
LET'S TALK ABOUT THE SPEED OF SOUND!
There is kind of a universal speed limit on sound. It can fluctuate depending on temperature, humidity, altitude, and things of that nature. But let's keep it simple and stick with the average of 343 m/s. In one second, sound can travel 343 meters, or 1,125.33 feet. Since we know a frequency has a certain number of cycles per second, and sound travels a specific distance per second, we can now figure out the wavelength of a frequency! For example, a 1kHz tone will complete 1,000 cycles over 1125 feet, so the wavelength, or distance from peak to peak is 1.126 feet! A lower frequency like 40Hz will have a wavelength of 28.133 feet! Because again, they're traveling the same distance, and a certain number of cycles need to be completed in that amount of distance.
These terms are the fundamentals of sound and how it travels. These are the building blocks on which we will make our way to EQ'ing vocals to make a clean, present, and inspiring mix. Make sure you are subscribed to the podcast so we can make it all the way through this journey together! Thanks!
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