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Audio Recording Mixing How Sound Works: How does sound work? So for this installment I'm going to go a bit on the technical side of things. Truth of the matter is what I'll be talking about isn't something you really need to know but I thought to talk about it cause in the future I will be using words that I will explain here. So lets get started. How does sound work? Well I can go all boring as a text book from high school and say sounds are vibrations. Everyone and their dog knows that, but sound doesn't vibrate the air. Wrong sound needs a medium to travel through to exist. This means that if you were in space no one could hear you scream. We hear sound cause objects that create sound vibrate the air particles. The way air particles move by hitting one another then going back to their original position is what creates sound waves. This movement is called Compression and Refraction. Don't worry about remembering that as its really a super nerdy thing I'm talking about just to lead up to what sound waves look like. Fig 1.1 Fig 1.2 This (Fig 1.1) is a sine wave, a perfect sound wave. They don't exist in the real world but for sake of conversation we shall use it. The bumps above are compression and the ones below are refraction as shown in Fig 1.2 blue being compression pink is refraction. Again this isn't something you need to know to be a good engineer but what is important is what is called a zero-crossing. Fig 2.1 A zero-crossing is the point where a sound wave is neutral. To save time and to make me not look like as big of a nerd that I really am I drew "X" where zero-crossing's are (Fig 2.1). Its very simple and I'm sure you can see the pattern so I'll leave it at that. So Wait a minuet why are zero-crossings important? Well have you ever heard annoying click noises in a song? Most of these clicks happen when a new section or riff comes into the song. There is a reason for that. And its called bad editing. Anytime you cut a piece of audio and its not on a zero-crossing its going to create that pop/ click sound. There are ways to avoid these clicks and pops and make editing easy without worrying about your zero's as much but I'll save that for my editing chapter. For now lets move on to frequency. I see a lot of confusion in this area. Often I see people thinking that instruments only exist in certain ranges. Truth is any sound you make has information in all frequency's. What makes a sound different from one another is how much of each frequency there is. I'm going to be quick on explaining what a frequency is cause it is very straight forward. First I ask and please don't cheat. Look at the sine wave picture I have been using and assume that is a sound made in one second. What frequency is it? Insert awesome Jeopardy music here. So have the answer? If you guessed 3Hz then you are correct. That is an extremely low sound, one that can't be heard since its a known fact that the averaged human can hear 20Hz to 20kHz. Well maybe not anymore with mp3's dominating the world. But back on point, if you were not able to figure that out don't worry I'm about to tell you how. Fig 3.1 A frequency is is determined by how many cycles happen in one second. So in other words when I say 200Hz that would be a sine wave happening 200 times per second. Fig 3.1 shows one wave cycle. So if I was to draw that wave form 200 times and say from beginning to end is only one second then we would have a 200Hz tone. Fig 4.1 Fig 4.2 So now that we know how a sound is made and how the tone is made lets get into phasing. Phasing is when sound cancels out. This happens when 2 opposite waveforms come together (Fig 4.1). in the example shown (Fig 4.1) the sine waves are completely out of phase. When something is completely out of phase no sound is created as a result. But if both sound waves were to be in phase (Fig 4.2) then what happens is the sound wave is the same but louder by 6dB(I'll go in detail what a dB is later). Fig 4.3 So far we assumed with using the same Wave form but what happens when you have 2 different sound waves combine together? (Fig 4.3) Well the answer is simple, a new waveform is created. Its more complex then just that but for sake of not confusing anyone with big words and math we will just say 2 different sound waves creates one completely different sound wave. Now on to Decibels or dB (yes its a small d first not a D). A decibel is best described as a ratio number we use to measure how loud something seems to be. There is many different types of measurements using dB but they all measure sound level. In the digital world what is called a peak meter is in fact a dBfs meter (Decibel Full Scale). This is often the meter people refure to when they talk about lowering something by so and so dB. We also use it in EQ, Compressors, and so on. Anything that alters how loud something is an Engineer will use dB for. So it makes sense that a lot of different dB meters exist but in today's age for mixing or recording purposes the dBfs meter or peak meter is the most important. The peak meter tells us where our max digital level is if we exceed 0dBfs what happens is our sound clips and distortion is created. This wants a huge issue back in the analog days since the clip distortion analog creates tends to sound musical but in the digital world when we clip we get harsh noise's. Because of that we try not to hit 0dBfs to avoid clipping What people don't realize is you can still clip without your meters saying you have. This usually happens when someone uses an EQ to boost something like the bass. What I found is people don't watch there meters on EQ's because of this when they boost they hit the EQ's 0dB ceiling and create distortion or they boost a frequency that for whatever reason gets past the meter and hits the ceiling. Looking back it seems I have talked about the basics of how sound is created and work's. There is other more advanced theory's that I could get into but I feel that I have already talked about a lot and would rather not lose anyone quite yet. Read this a few times ask questions to gain more understanding if something I said confused you. As for now I'm going to call it a chapter. The next chapter I'm not sure what I'm going to talk about, if you have any ideas as to what you would like to know make it known and I'll do my best to write about it. For now this is Joey R aka Joeyshoelace Wishing you all a Happy Mixing.
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