Before you work with audio, there are some digital audio fundamental terms that you need to understand. These words span from sound waves and frequencies to audio bit depth and sample rate. What do you need to know about sound waves and frequencies? In this video, author Cheryl Ottenritter explains what they are.
- Okay, so we're going to jump right into the science of sound by talking about sound waves and sample rate. Keep in mind that sample rate and bit depth have everything to do with sound waves, their frequencies and their amplitudes. Sound is created by vibrations caused by pressure and release all around us. These compressions and rarefactions cause movement through plasma, liquid and even solids. This repetitive action forms a pattern that are called sound waves.
So, when we're talking about a sound wave you have certain basics of a sound wave. So, you have a component called the wavelength. The wavelength is an exact cycle from crest to trough of a full cycle of sound. And then the amplitude is how loud it is. How much that compression and rarefaction is on the air around us or the plasma or the liquid is the loudness or the amplitude. And you can see that easily how high or how low the peak and the trough are.
When we talk about amplitude, one way to really understand that amplitude is the energy of the sound wave, is when you jump into Premier you can see the energy of this wave. It's right there. If you do G, and you adjust the gain or the energy by say minus 10, you can see the actual energy of those wave forms or those sound waves go down. It's volume yes, but it's the actual energy of the sound wave. And likewise you can have it go back up.
Let's do five, and you can see that the actual energy of the sound wave is changing. We're not in Audio Units right now, so you can't really go into the sound wave so we go back into Show Audio Units. So then you can use your plus sign to zoom in and you can see the wave form. So, let's do G again, and do five and you can see how the sound waves, the samples, are actually jumping and they're becoming larger. That's how you know the energy of this sound wave is changing.
Not just the volume, but the actual energy of the clip of the wave is changing. So we go back in, we want to do even more so we can see how aggressive that can be. You can see exactly how, woo, that amplitude, that energy of that clip is super hot now. Wavelength is measured in hertz. So, it's equivalent to one cycle per second is one hertz. So how many cycles is in one second is how many hertz that you have. This gives you a better idea of what is happening with the sound wave.
The speed or time that the sound travels determines the frequency or pitch. If there's one cycle per second, the frequency is one hertz. If there's 20 cycles per second, it's 20 hertz. 4,000 cycles is 4K hertz. We hear or perceive 20 hertz to 20,000 hertz typically. With the sound wave, the longer the sound wave, the deeper the pitch. The shorter the sound wave the higher the pitch. The more that the sound wave is large from top to bottom, from the peak to the trough, is the amplitude and that is the energy of the wave frame.
Now, if we jump into Premier we can see what a sound wave is. And a lot of times people feel like well I don't see samples, I don't see sound waves or I don't really perceive those in my NLE and in Premier you have to go into Show Audio Units to actually see the sample. So, if we jump into Premier, just very quickly here, and we go to the Timeline Panel, go and click on Show Audio Time Units. When you do that you can suddenly see that we have all these numbers right here.
Hours, minutes, seconds and then these are the frames or the samples. And the way that Premier does it is it gives you, depending on your sample rate of your session, will tell you how many samples that you have here. So, in this case we're on 48K so you can see that you start to have 48 samples that you're able to see. So, let's zoom in here and we'll start to see samples. Let's find, get a little bigger, so that you can actually see the samples coming in.
Now if you turn off Audio Units, then suddenly you're really not able to get down into the samples, see how it stops at a frame. So that is the sample and then as you're looking at it you can see the various heights and troughs and the volume of the sample. So, one thing to always remember as you're thinking of sound wave is that these lower frequencies and these higher frequencies are actually all around us.
It's not just some phantom in the air or just in your NLE, they're actually sound waves that have length. For instance, a 50 hertz is 22 and a half feet long. That's really long; whereas, 5,000 hertz is only 2.7 inches. You start to get an idea of really what sound is all around us. And that's really super important when you're thinking about low frequencies in your edit suite. For instance, if it's 22 and a half feet long, that's very, very long so you're going to have to contain that somehow or manage that.
Otherwise, it starts to build up. And that's for another class, but just keep in mind that might be why you're hearing a lot of bass in your edit suite. Moving along then, we're going to talk a little bit about how the frequency of what you're hearing and what it is sound wave wise. And then we going to start training you're ears to understand what the sound wave is so that you can more correlate that when you're in the field. What is that sound that's bothering me? How is that? What frequency is that? Is that really going to matter if I roll that off or if I try to take that out in the field or should I wait til post? Start that whole fundamental learning by learning what frequencies some basic sounds are.
So those are the components of a sound wave and we're starting to learn those fundamentals and how they deal with frequency is really, really important. So, now we're going to go into Premier and learn how you can start using Premier to help understand frequency and pitch.
- Identifying audio frequencies
- How sample rate is used in digital audio
- Using audio meters for a better mix
- Signal flow and gain stages
- Mixing with perceived loudness (LKFS) in mind
- Common audio deliverables