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Whether one is producing music, podcasts, game sounds, or film sound effects, Digital Audio Principles provides the tips and techniques that will make the project a success. Author Dave Schroeder explains the basics of digital audio production techniques and covers the essential hardware and software. He also discusses sound theory, frequency response, the range of human hearing, and dynamic range.
Now let's take a look at plug- ins that deal with dynamics; that means plug-ins that affect the dynamic range of a sound. Now, these effects work kind of based on the relationship of a sound to a threshold. A threshold is a certain level of volume that you set that once the sound interacts with it, the Dynamics plug-in is going to do something to that sound. There are basically two kinds of effects in the dynamics processing world. There are those that care about any sound that goes above the threshold, and then there are those that care about what sounds don't make it up to the threshold, or live below the threshold.
So, let's start by taking a look at those that care about the sounds that go above the threshold. These are known as compressors or limiters. So, a compressor and a limiter are kind of the same animal; they are just different degrees of effect. We'll start by kind of talking about the compressor, and then show you that the limiter is really the same thing, just with one setting slightly different. So, in this graph, I'm representing sounds, volume levels, like in your meters, and I've set a threshold here, and I've decided that this is the threshold.
So, when a sound stays below that threshold, we're not going to have any effect. In all these little two-bar graphs, I have the initial sound, and then this represents what's actually happening, what they compressor does to that sound. So, if a sound doesn't hit the threshold, if it's not loud enough, it gets left alone, and it sounds the way it sounds. If a sound goes beyond the threshold, then what the compressor does is it actually compresses that sound, the volume of that sound, back down. It does it according to a ratio, which I've got up here.
In this situation, we have a 1:1 ratio. So, for every one DB--let's say these lines are different one DB, two DB, three DB--for every one DB we go above the threshold, the compressor is going to turn that sound down by one DB. So we have a 1:1 ratio. In this instance, we have a 2:1, and our sound has gone above at 4 DB. As a result, we're going to push that down two, which means for every two DB it goes above the threshold, push it down by one.
That's your 2:1 ratio. Now, this is really helpful for keeping sounds obviously at a kind of consistent volume. Anything that goes above that threshold, we want to bring it kind of back closer to our threshold, because that's the volume we want to keep things at. This is really useful if you're working on something like a voiceover where there is lots of loud transients. You kind of want to make everything about the same volume, so that when other people listen back to it, they don't have to strain to hear quiet parts, and then there are loud parts. There's a way of kind of leveling things off. Now the limiter is basically the extreme version of that.
It does what it's called. It limits the sound. So, when you set the threshold with a limiter, it doesn't matter how much louder that sound is than the threshold, you're always going to get that sound. Now this seems like, well, why wouldn't we always use that? But the problem is that the way dynamics work is that you're really turning down the volume. It's like if you can imagine sitting there and turning a volume knob really fast. You know what that sounds like, that there's an unevenness, their volume changes, and to the human ear we can hear that. So, a limiter actually, a lot of times when it's used, sounds kind of unnatural, because we know that there is some forceful dynamic changes going on there.
We use a compressor because it's a little bit more of a natural-sounding effect, but you'll use both of them in audio quite a bit. We'll show you a few examples, and I'll show a couple examples in this movie. Next let's look at an image for the expander, or gate. These are the Dynamics plug-ins that are concerned about the sounds below the threshold. Again, we've got the same sort of setup: a threshold, volume, and sounds coming up. But this time, we're interested in sounds below the threshold. Any sound that doesn't make it up to the threshold basically doesn't qualify.
If you can't make it to the threshold, we don't care about you, and we don't want to hear you. So, we assign a ratio to turn things down that are below that threshold. So, in this case, we've got a sound that's not quite loud enough. We've pushed that sound back down. Now, this is useful if you have a track where someone is speaking, but in between when they're speaking, there is a little bit of background noise that's kind of quite, but you wish it was a lot quieter. This can be useful in terms of when the person starts to speak, if we set the threshold so that their voice just breaks the threshold, we'll always hear them speak.
But then when they're done, we'll have the volume of the rest of the background noise pushed back down. So, it allows us to separate the volume difference between what we want to hear and what we don't want to hear. A gate, kind of like the way the limiter is the extreme version of the compressor, the gate is kind of the extreme version of the expander. It's basically an open-and-shut deal. It's like a garage door: either you can pull in or you can't. There's no, well, if you make it, we'll give you a little bit. We've set the threshold, and any sound that doesn't make it over that threshold is squashed, and we don't hear it at all.
So, anything that doesn't make it up to our threshold, we never hear. We'll show you an example of this. It's great for using this on things like drums, or things where you want kind of a real fast open-and-close situation. I should also mention that we're looking at expanders as downward expanders. But there is also a way commonly to set an expander to work as an upward expander in which sounds above the threshold are actually turned up. As opposed to turning down the quiet sounds and moving the noise down, we're taking what we want here, like the voiceover, and making it even louder.
But generally, assuming that you've set your recording levels well and gotten a full signal, you'll probably be using a downward expander most of the time. Now, let's go back into Pro Tools and open a few of these up, and take a look at how they actually work with sound files.
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